U.S. patent application number 13/378991 was filed with the patent office on 2012-05-17 for blood filter and method for filtering blood.
This patent application is currently assigned to Leukocare AG. Invention is credited to Stefan Margraf, Martin Scholz.
Application Number | 20120118825 13/378991 |
Document ID | / |
Family ID | 41211979 |
Filed Date | 2012-05-17 |
United States Patent
Application |
20120118825 |
Kind Code |
A1 |
Margraf; Stefan ; et
al. |
May 17, 2012 |
BLOOD FILTER AND METHOD FOR FILTERING BLOOD
Abstract
The present invention relates to a method for filtering blood to
produce plasma or serum and to a blood filter for the production of
plasma or serum from a blood sample. The invention further relates
to a kit comprising a blood filter for the production of plasma or
serum from a blood sample and a syringe.
Inventors: |
Margraf; Stefan;
(Frankfurt/Main, DE) ; Scholz; Martin; (Oberursel,
DE) |
Assignee: |
Leukocare AG
Munchen
DE
|
Family ID: |
41211979 |
Appl. No.: |
13/378991 |
Filed: |
June 17, 2010 |
PCT Filed: |
June 17, 2010 |
PCT NO: |
PCT/EP2010/058551 |
371 Date: |
January 30, 2012 |
Current U.S.
Class: |
210/645 ;
210/321.6 |
Current CPC
Class: |
B01D 63/087 20130101;
A61M 1/3403 20140204; A61M 2205/3331 20130101; G01N 33/491
20130101; A61M 1/34 20130101; B01D 2313/10 20130101 |
Class at
Publication: |
210/645 ;
210/321.6 |
International
Class: |
B01D 61/00 20060101
B01D061/00; B01D 63/00 20060101 B01D063/00 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 17, 2009 |
EP |
09163006.1 |
Claims
1. A method for filtering blood to produce plasma or serum,
comprising the steps of: (a) providing a blood filter comprising a
filter membrane having opposite first and second sides and a
receiving compartment defining a hollow space; and (b) inserting a
blood sample into said receiving compartment, wherein the volume of
said hollow space is 3 to 20 times larger than the volume of said
blood sample, thereby increasing the gas pressure within said
receiving compartment so that said blood sample is filtered by said
filter membrane, and wherein said plasma or serum comprised in said
blood sample is forced through said filter membrane.
2. The method of claim 1, wherein said blood sample is inserted
into said receiving compartment via a syringe or a pipette only
filled with said blood sample.
3. A method for filtering blood to produce plasma or serum,
comprising the steps of: (a) providing a blood filter comprising a
filter membrane having opposite first and second sides and a
receiving compartment having a first volume; (b) inserting a blood
sample and a gas into a syringe having a plunger, the blood sample
occupying a second volume and the gas occupying a third volume in
the syringe; (c) connecting said syringe to said blood filter to be
in fluid communication with each other; and (d) increasing the
pressure within said syringe by moving the plunger to a position
such that the third volume is compressed by between 1/20 to 1/5, so
that said blood sample is filtered by said filter membrane, wherein
said plasma or serum comprised in said blood sample is forced
through said filter membrane.
4. The method of claim 3, further comprising the step e) of
compressing the first and third volume by pressing down the plunger
of said syringe beyond a position where the blood sample is
received by said receiving compartment.
5. The method of claim 1, wherein said receiving compartment has at
least one opening covered with said first side of said filter
membrane.
6. A kit comprising a blood filter for the production of plasma or
serum from a blood sample and a syringe; the blood filter
comprising a filter membrane having opposite first and second
sides; a receiving compartment defining a hollow space for
receiving a blood sample to be filtered from said syringe, said
receiving compartment having at least one opening covered with said
filter membrane, wherein said first side is facing the receiving
compartment, and wherein the hollow space of said receiving
compartment has a first volume; and a sampling compartment being
arranged on said second side of said filter membrane; wherein the
syringe is adapted to receive a predetermined second volume of
blood sample; and wherein the first volume is 3 to 20 times larger
than the second volume.
7. A kit comprising a blood filter for the production of plasma or
serum from a blood sample and a syringe; the blood filter
comprising a filter membrane having opposite first and second
sides; a receiving compartment defining a hollow space for
receiving a blood sample to be filtered from said syringe, said
receiving compartment having at least one opening covered with said
filter membrane, wherein said first side is facing the receiving
compartment, and wherein the hollow space of said receiving
compartment has a first volume; and a sampling compartment being
arranged on said second side of said filter membrane; wherein the
syringe is adapted to receive a predetermined second volume of
blood sample and a predetermined third volume of a gas; and wherein
the syringe is adapted to compress the third volume by between 1/20
to 1/5 of the third volume.
8. The method of claim 1, wherein the first volume of said hollow
space or the sum of said first and third volume is at least 0.3
ml.
9. The method of claim 1, wherein said receiving compartment is
made from a material that is adapted to withstand an internal
pressure of at least 7 kPa, preferably at least 18 kPa, more
preferably at least 35 kPa without substantial deformation,
preferably from a substantially inelastic and/or rigid
material.
10. The method of claim 1, wherein at least 50%, preferably at
least 75%, more preferably at least 90%, and most preferably at
least 95% of the surface area of the second side of said filter
membrane is covered.
11. The method of claim 10, wherein the second side of the membrane
is in contact with a substantially flat substrate, wherein said
flat substrate is preferably part of the sampling compartment.
12. The method of claim 1, wherein the filter further comprises a
hydrophilic and porous sheet arranged on the first side of said
filter membrane in said receiving compartment which is preferably
covering said filter membrane, wherein said porous sheet is made of
fibrous material.
13. The method of claim 1, wherein said receiving compartment
comprises a sample insertion means, which is a one-way-valve.
14. The method of claim 1, wherein said sampling compartment
comprises an outlet.
15. The kit of claim 7, wherein the syringe comprises a plunger and
a first stop for the plunger of the syringe to stop the plunger
during suction or pulling.
16. The kit of claim 15, wherein the syringe comprises a second
stop for the plunger of the syringe to stop the plunger during
pushing downwards in order to limit the compression of the third
volume.
17. The kit of claim 16, wherein the first and second stops are
arranged such that the third volume is compressed by between 1/20
to 1/5 of the third volume.
18. The kit of claim 6, wherein the syringe comprises means to
arrest the plunger thereof in a predetermined position.
19. A method of filtering blood to produce serum or plasma
comprising using the kit of claim 6.
20. A blood filter for the production of plasma or serum from a
blood sample, comprising: a filter membrane having opposite first
and second sides; a receiving compartment defining a hollow space
for receiving a blood sample to be filtered, said receiving
compartment being arranged on said first side of the filter
membrane, the filter membrane resting on a seating, wherein at
least 50% of the surface of the second side of the filter membrane
is in contact with said seating, and wherein the seating comprises
a plurality of channels for collecting the filtered blood
sample.
21. The filter of claim 20, wherein the seating is convex having a
radius of curvature between 30 and 150 mm.
22. The filter of claim 20, wherein at least 75%, of the surface of
the second side of the filter membrane is in contact with said
seating.
23. The filter of claim 20, wherein the plurality of channels cover
between 0.5 and 15% of the surface of the seating.
24. The filter of claim 20, wherein the plurality of channels forms
a sampling compartment having a volume in the range between 0.06
mm.sup.3 and 3.5 mm.sup.3, per cm.sup.2 of the filter surface.
25. The kit of claim 6, wherein the first volume of said hollow
space or the sum of said first and third volume is at least 0.3
ml.
26. The kit of claim 6, wherein said receiving compartment is made
from a material that is adapted to withstand an internal pressure
of at least 7 kPa, preferably at least 18 kPa, more preferably at
least 35 kPa without substantial deformation, preferably from a
substantially inelastic and/or rigid material.
27. The kit of claim 6, wherein at least 50%, preferably at least
75%, more preferably at least 90%, and most preferably at least 95%
of the surface area of the second side of said filter membrane is
covered.
28. The kit of claim 27, wherein the second side of the membrane is
in contact with a substantially flat substrate, wherein said flat
substrate is preferably part of the sampling compartment.
29. The kit of claim 6, wherein the filter further comprises a
hydrophilic and porous sheet arranged on the first side of said
filter membrane in said receiving compartment which is preferably
covering said filter membrane, wherein said porous sheet is made of
fibrous material.
30. The kit of claim 6, wherein said receiving compartment
comprises a sample insertion means, which is a one-way-valve.
31. The kit of claim 6, wherein said sampling compartment comprises
an outlet.
32. The kit of claim 31, wherein the outlet comprises a universal
adaptor.
Description
[0001] The present invention relates to a method for filtering
blood to produce plasma or serum and to a blood filter for the
production of plasma or serum from a blood sample. The invention
further relates to a kit comprising a blood filter for the
production of plasma or serum from a blood sample and a
syringe.
[0002] In this specification, a number of documents including
patent applications and manufacturer's manuals are cited. The
disclosure of these documents, while not considered relevant for
the patentability of this invention, is herewith incorporated by
reference in its entirety. More specifically, all referenced
documents are incorporated by reference to the same extent as if
each individual document was specifically and individually
indicated to be incorporated by reference.
[0003] The filtration of blood to separate solid blood components
from serum or plasma is a necessary step to enable for the
determination of the presence and/or concentration of compounds
dissolved in the blood starting from serum or plasma. By now, most
filtration methods rely on a centrifugation step and no feasible
alternative methods have been suggested so far. However,
centrifugation is time consuming and poses problems in particular
in developing countries since the institutions there often lack
suitable centrifuges and therefore cannot carry out the essential
step necessary to obtain the basis material for determining the
presence and/or concentration of compounds dissolved in the
blood.
[0004] Membranes for filtering blood in order to obtain plasma or
serum have been recently developed and are disclosed e. g. in U.S.
Pat. No. 6,939,468 and U.S. Pat. No. 7,125,493. However, no device
has been developed yet which enables for the rapid production of
serum or plasma without a centrifugation step.
[0005] Hemolysis, i. e. the destruction of red blood cells leading
to the liberation of haemoglobin, is an unwanted side effect in
many techniques for blood filtration. It usually occurs if the
pressure applied is too high, which leads to excessive pressure
difference and shear force destroying erythrocytes. Hemoglobin,
however, interferes with many uses of plasma or serum so that
hemolysis should be avoided in the production of serum or
plasma.
[0006] Therefore, there is a need for a device and/or method
enabling for producing serum or plasma for further analysis without
centrifugation and without hemolysis. Such a device and/or method
should furthermore or alternatively be cost effective.
[0007] Accordingly, the present invention relates to a method for
filtering blood to produce plasma or serum, comprising the steps
of:
[0008] a. providing a blood filter comprising a filter membrane
having opposite first and second sides and a receiving compartment
defining a hollow space; and
[0009] b. inserting a blood sample into said receiving compartment,
wherein the volume of said hollow space is 3 to 20 times larger
than the volume of said blood sample, thereby increasing the gas
pressure within said receiving compartment, preferably to force
said blood sample against said filter membrane, so that said blood
sample is filtered by said filter membrane, and wherein said plasma
or serum comprised in said blood sample is forced through said
filter membrane.
[0010] The term "plasma" relates to the liquid phase of the blood
obtained after separation of its solid constituents such as cells
(leukocytes, erythrocytes etc.) which can still coagulate.
[0011] The term "serum" relates to the liquid fraction of blood
which is obtained after coagulation of the blood by separation of
the cruor formed by the cellular constituents of the blood,
thrombocytes and coagulation factors.
[0012] Depending on the filter membrane used, the serum or plasma
obtained from the blood filter of the invention may still comprise
at least a part of the thrombocytes comprised in the blood applied
to the filter. Whether this is the case depends, inter alia, on the
filter membranes used.
[0013] The filter membrane comprised in the blood filter of the
invention is suitable to filter blood in order to obtain plasma or
serum. Membranes for filtering blood in order to obtain plasma or
serum have been recently developed and are disclosed e. g. in U.S.
Pat. No. 6,939,468 and U.S. Pat. No. 7,125,493. Suitable filter
membranes may comprise e. g. polyethylene terephthalate (such as
available e. g. from Sekisui in a product for the production of
serum) or polysulfone (such as the Vivid Plasma Separation Membrane
available from Pall).
[0014] A blood sample is a sample comprising blood of an
individual. Individuals comprises any animal which uses blood for
the transportation of oxygen and/or nutrients. Preferably, the
individual is a human.
[0015] The present inventors have surprisingly found that a
distinct assembly of features in a blood filter and/or the
application of distinct features in a method enables for the rapid
production of serum or plasma for further analysis with
substantially no hemolysis. A principle underlying the present
invention is the ratio of the volume of the hollow space in front
of the filtering membrane and that of the blood to be filtered
which is preferably between 3:1 and 20:1. This ratio has been found
to be beneficial to enable to separate blood without hemolysis
based on pressure applied. It is based, in part, on the
construction of the blood filter of the invention, the surface of
the filter membrane and its resistance for air. In accordance with
the invention, a volume of blood is filled into the receiving
compartment in a way that the gas within said compartment is
compressed thus rising the pressure in said receiving
compartment.
[0016] The present method/device is based on a blood filter
comprising a filter membrane having opposite first and second sides
and a receiving compartment, wherein said receiving compartment
preferably is one inseparable piece. Exemplary blood filters
applicable in the method of the invention are depicted in FIGS. 1,
3, 5, 7, 9 and 10.
[0017] In the present method, a blood sample having a defined
volume is filled into an insertion means, such as a syringe or a
pipette. Preferably, the insertion means only comprises said blood
sample and, preferably substantially, no air or other compressible
gas. In other words, said syringe or pipette is preferably filled
with said blood sample only. Said insertion means is then attached
to the receiving compartment of said blood filter, either directly
or via an adapter, so that both are in fluid communication. The
plunger of said insertion means is then pressed down thereby
inserting the blood sample into the receiving compartment. Thereby,
the internal pressure within said receiving compartment will be
increased to reach a stable magnitude. Said stable magnitude will
usually be reached immediately after the blood sample has been
inserted into the receiving compartment and preferably covers said
filter membrane. Prior to covering, a small amount of air or other
gas which is comprised in said receiving compartment will run
through the pores of said filter membrane. Therefore, it is
envisaged that the blood sample be inserted rapidly into said
receiving compartment, preferably such that it, preferably also
rapidly, covers said filter membrane. In this regard, "rapidly"
comprises a time of between 0.5 and 5 s, preferably between 0.5 and
3 s, until the filter membrane is covered which may result in a
loss of about 1/20 to 18/20 of the air or other gas comprised in
said receiving compartment.
[0018] The increased internal pressure obtained after coverage of
the filter membrane with the blood sample forces the solid
components of the blood sample against and, at least in part, into
and the serum or plasma through said filter membrane so that it may
be collected on the second side of said filter membrane located on
a sampling compartment while remaining components of the sample
remain in the filter medium.
[0019] The pressure applied to the receiving compartment is in fact
a pressure difference of the internal pressure as compared to the
pressure surrounding the filter. The resulting internal pressure
after inserting the blood sample and coverage of the filter
membrane by said blood sample is preferably essentially constant.
This may be achieved by holding down the plunger of the insertion
means but in many cases also by simply relieving the plunger. This
is because the pressure applied as compared to the surrounding
pressure is so low that the resistance of the plunger within the
insertion means, e. g. the syringe, is so high that it will remain
at the position that it had after pressing it down. Alternatively,
the syringe may further comprise a means to lock the plunger at the
desired position. Additionally or alternatively the opening of the
receiving chamber into which the sample is provided is a one way
valve.
[0020] The present invention also relates to a method for filtering
blood to produce plasma or serum, comprising the steps of:
[0021] a. providing a blood filter comprising a filter membrane
having opposite first and second sides and a receiving compartment
having a first volume;
[0022] b. inserting a blood sample and a gas into a syringe, the
blood sample occupying a second volume and the gas occupying a
third volume in the syringe;
[0023] c. connecting said syringe to said blood filter to be in
fluid communication with each other; and
[0024] d. increasing the pressure within said syringe, preferably
due to pushing the plunger until the blood sample is received by
said receiving compartment, preferably by at least 1/20 of the
third volume, preferably between 1/20 and 4/20 and preferably about
2/20, beyond the point of equalized pressure inside and outside of
the blood filter, i.e. inside the syringe and inside the receiving
compartment, thereby preferably forcing said blood sample against
said filter membrane, so that said blood sample is filtered by said
filter membrane, wherein said plasma or serum comprised in said
blood sample is forced through said filter membrane.
[0025] It may be preferable that the sum of first and third volume
is 3 to 20 times larger than the second volume, under ambient
pressure.
[0026] For this embodiment as well as the other embodiments of the
present invention described further below, the explanations and
definitions given for the blood filter of the invention are
applicable since the principles underlying the blood filter of the
invention and the method of the invention are substantially the
same. This does not exclude that means and blood filters other than
that according to the invention may be used in the method of the
invention.
[0027] In this alternative or additional embodiment, the first
volume formed by the receiving compartment is comparably small and
preferably approaches zero. The present method is also based on a
ratio of volumes which, in this case, is that between the first and
third volume formed by the syringe and the receiving compartment
and the narrowing volume which is the volume along which the
plunger is pushed beyond the point of equal pressure inside and
outside of the blood filter, i.e. inside the syringe and inside the
receiving compartment. This narrowing amount is about 1/20-4/20 of
the third or gas volume. After inserting the blood sample and the
appropriate volume of gas into the syringe, said syringe is
connected to said blood filter to be in fluid communication
therewith. This means that said syringe may be directly attached to
said filter or that both may be connected via an adapter or a
tubing which preferably has only a small dead volume. After the
connection has been established, the pressure within said syringe
is increased until the blood sample is received by said receiving
compartment. This is preferably effected in a way that, prior to
any gas entering the receiving compartment, said blood sample is
received by said receiving compartment. More preferably, during
pressure increase, the syringe is held down so that the blood
enters said receiving compartment first. The syringe may further
comprise a means to arrest the plunger at the desired position. As
described above, the internal pressure within said receiving
compartment will usually be increased immediately after the blood
sample covers said filter membrane. Prior to covering, an amount of
air or other gas which is comprised in said receiving compartment
will run through the pores of said filter membrane. Therefore, it
is envisaged that the blood sample be inserted rapidly into said
receiving compartment. Upon the pressure increase after the filter
membrane being covered with said blood sample, said blood sample is
forced into said filter membrane and plasma or serum comprised in
said blood sample through said filter membrane, as also discussed
above.
[0028] For example, using a blood filter described above, a volume
of blood is to be filled into a syringe as well as a volume of air,
preferably being about 3-20 times the volume of the blood. After
connection to the filter the plunger has to be pushed to a certain
extent, e.g. depending on the actual blood filter characteristics.
When the receiving compartment is filled with blood and the
membrane is all wet, preferably a point of equalized pressure
inside and outside of the blood filter, i.e. inside the syringe and
inside the receiving compartment is reached. Then, further pushing
of the plunger leads to a pressure increase compressing the air in
the syringe by at least 1/20 up to about 4/20 of the volume of air
inside the syringe.
[0029] Due to loss of gas through the filter until the complete
filter is wetted with blood, the resulting compression of gas is
less than the practically applied compression. The effective
compression is between 1/20 and 4/20 (typically 2/20, blood/gas
respectively), resulting in a pressure increase of about 5-20 kPa.
The practical ratio of the volumes of gas and blood is between 3:1
and 20:1. The exact ratio applied depends on the time needed until
the membrane is wetted and the loss of gas until then. The loss of
gas again depends on the resistance of airflow of the membrane as
well as that of the capillaries until the gas passes the
outlet.
[0030] Using filter membranes such as the Pall Vivid membrane,
typically a sample volume of ca. 100 .mu.l (minimum of 25-35
.mu.l/cm.sup.2 filter membrane, maximum 600 .mu.l/cm.sup.2 filter
membrane) blood per cm.sup.2 filter-membrane is sufficient in order
to obtain an amount of serum or plasma sufficient to carry out most
diagnostic evaluations. The surface of the filter membrane is not
limited, but would in practical terms be preferably at least 1
cm.sup.2. Commonly applied surfaces of the filter membrane would
preferably be between 2 and 20 cm.sup.2, preferably between 3 and
10 cm.sup.2.
[0031] On the example of a membrane of 6 cm.sup.2 and a blood
sample of ca. 600 .mu.l, the membrane will be all wet in between 1
and 5 seconds. If a porous sheet on top of the membrane is used as
will be described further below, the wetting time can be shortened
such that the membrane will be wet within 0.5-3 seconds. If a disc
to channel the blood is used, as also described further below, the
delay between the application of blood and wetting the membrane is
approaching the time needed to fill the blood into the blood
filter. If blood in excess (150-600 .mu.l/cm.sup.2 filter membrane)
is used, the wetting time is also considerably shorter. After
filling, the filtration starts. It takes typically 20-60 seconds
until the filter is blocked due to erythrocytes. Using 6 cm.sup.2
of the pall membrane, an output of 60-120 .mu.l plasma could be
obtained.
[0032] In another preferred embodiment the filter comprises an
outlet which is closed during the filling with blood and opened
after the membrane is fully wet. Such a blood filter will need a
volume ratio between 20:1 and 20:4 (gas/blood) only.
[0033] The pressure arising from the gas being compressed, which
effectively is the pressure difference of the gas pressure in the
filter prior to applying the blood sample (usually atmospheric
pressure) and after wetting the filter membrane with blood is
necessary and sufficient to force the blood applied into the filter
membrane the porous structure of which provides the only escape for
gas and/or liquid to relieve said pressure. In said filter membrane
the cellular components of the blood, in particular red and white
blood cells, but also thrombocytes if desired, are separated from
the liquid fraction which is serum or plasma, depending on whether
an anticoagulant had been added to the blood prior to filtration or
not. The defined ratio of the volume of the receiving compartment
and the blood sample leading to a defined pressure within said
receiving compartment thus largely prevents that an overpressure is
created which results in hemolysis.
[0034] According to the invention, the volume of the hollow space
of said receiving compartment is between 3 and 20 times larger than
the volume of the blood sample to be filtered. Preferably,
corresponding to the first embodiment of the invention the volume
of said hollow space is between 3 and 6 times larger, exemplified
on a blood filter according to FIGS. 1, 5 and 9, or between 3-8
times larger exemplified on a blood filter according to FIGS. 3, 7
and 10 than the volume of the blood sample to be filled in the
blood filter. The blood filled into the receiving compartment will
wet the membrane and compress the air inside the receiving
compartment which is preferably resulting in an effective
compression rate of 4/20-1/20 of the second and/or third volume
(pressure of about 5-20 kPa difference to ambient) including the
loss of air through the membrane before completely wet.
[0035] Preferably, and corresponding to the second embodiment of
the invention the compression rate of the gas, which volume is
preferably 3-20 times larger than the volume of blood in the
syringe, exemplified on a blood filter according to FIGS. 2, 4, 6,
and 8, is preferably between 4/20-1/20 of the second volume plus
the volume of the receiving compartment to be filled, i. e. the
third volume. Practically, the volume narrowing in the syringe
using the plunger is a little more than indicated above accounting
to the loss of gas through the membrane until fully wet, and is
preferably about 2/20-6/20 of the sum of the volume of the gas and
the volume of the receiving compartment.
[0036] In both embodiments the gas volume is narrowed in the range
of 1/3-1/20, preferably resulting in a working pressure difference
of about 5-20 kPa because of some loss of air.
[0037] In a preferred embodiment, the method further comprises the
step e) of compressing the first and third volume by pressing down
the plunger of said syringe beyond a position where the blood
sample is received by said receiving compartment, preferably
wherein a time lag is provided between steps d) and e).
[0038] This additional step is preferably to be carried out if the
volume of gas pressed through said filter membrane prior to the
filter membrane being completely covered with the blood sample is
more than 3/20.
[0039] In another preferred additional or alternative embodiment of
the methods according to the invention, said receiving compartment
has at least one opening covered with said first side of said
filter membrane.
[0040] The opening comprised in said receiving compartment is at
least partially covered with said first side of said filter
membrane. Preferably, the opening is fully covered with said first
side of said filter membrane. In any case, the opening, if not
fully covered with said first side of said filter membrane, is
covered with a different material to the extent that it is not
covered with said first side of said filter membrane. In other
words, if said opening is not fully covered with said first side of
said filter membrane, the remaining part of the opening is covered
with a different material. Such material may comprise a ring-like
structure arranged at the boundary of the receiving compartment to
fix said filter membrane.
[0041] The filter membrane covers the opening comprised in said
receiving compartment and preferably separates said receiving
compartment from said sampling compartment, preferably such that
the first side of said filter membrane faces towards the receiving
compartment.
[0042] The present invention also relates to a blood filter for the
production of plasma or serum from a blood sample, preferably
according to the method underlying the invention, comprising: a
filter membrane having opposite first and second sides; a receiving
compartment defining a hollow space for receiving a blood sample to
be filtered, said receiving compartment having at least one opening
covered with said filter membrane, wherein said first side of said
filter membrane is facing said receiving compartment, and wherein
the hollow space of said receiving compartment has a volume being 3
to 20 times larger than the volume of the blood sample to be
filtered; and a sampling compartment being arranged on said second
side of said filter membrane.
[0043] In a preferred embodiment of the methods or the filter of
the invention, the volume of said hollow space or the sum of said
first and third volume is at least 0.3 ml.
[0044] Common volumes of said hollow space or the sum of said first
and third volume are between 0.3 and 30 ml, depending on the
surface of the filter-membrane, preferably between 1.5 and 25 ml,
more preferably between 2 and 15, such as 3, 4, 5, 6, 7, 8, 9, 10,
11, 12, 13, 14 ml and any value in between these values.
[0045] The pressure suitable to filter blood to produce serum or
plasma should preferably lie between 5 and 20 kPa. A pressure of
about 10 kPa is generated if a gas such as air is compressed by
1/10 of its volume. With these features, a syringe can be
constructed the plunger of which can move only corresponding to e.
g. 1/10 of its entire volume.
[0046] Using this kind of system for obtaining blood and filling
that the blood into the filter blood filter according to FIGS. 2,
4, 6 and 8, the correct pressure applied for a sufficient amount of
time leads to a sufficient amount of plasma or serum.
[0047] In another preferred embodiment a pipette can be used
instead of a syringe, especially for small volumes.
[0048] In a preferred embodiment of the methods or the filter of
the invention, said receiving compartment is made from a material
that is adapted to withstand a pressure difference of at least 7
kPa, preferably at least 18 kPa, more preferably at least 30 kPa
without substantial deformation.
[0049] In another preferred embodiment of the method or the filter
of the invention, said receiving compartment is made from a
substantially inelastic and/or rigid material, which inelasticity
or rigidness may also be achieved based on the thickness or the
material used. Exemplary materials are inelastic plastics, like
polycarbonate, polystyrol, polvinylchloride, polyethylene,
polypropylene, polyurethane, polyethersulfon and mixed compounds
etc.
[0050] It is further preferred that, preferably in addition to said
receiving compartment, said sampling compartment is made from a
material that is adapted to withstand an internal pressure of at
least 7 kPa, preferably at least 18 kPa, more preferably at least
30 kPa without substantial deformation.
[0051] Alternatively or in addition to the above definition of the
material of the receiving and/or sampling compartment, the volume
of the receiving and/or sampling compartment is not enlarged by
more than 10%, preferably 5%, more preferably 1% upon application
of a pressure between 6 and 25 kPa.
[0052] In a preferred embodiment, said receiving compartment and
said sampling compartment, prior to use, are filled with a gas,
preferably air, under atmospheric pressure.
[0053] Suitable gases other than air comprise commonly applied
gases such as inert gases (argon, helium, neon), nitrogen or carbon
dioxide.
[0054] A further preferred feature of the blood filter of the
present invention is that at least 50% of the surface of the second
side of the filter membrane is covered. In this regard, the term
"covered" relates to the direct contact of one material, e. g. the
filter membrane, with another material, e. g. another substrate
comprised in the sampling compartment. In the course of the present
invention, it was surprisingly found that the coverage of the
second side of the filter membrane to a certain extent, such as at
least 50%, promotes the yield of serum or plasma from the
filtration process. Preferably, said serum or plasma is channelled
towards the outlet of the blood filter to be collected. The
efficiency of the filtration process increases with the percentage
of the filter membrane covered. This feature is minimizing the dead
space as well. This apparently contradictory result is not obtained
if fluids other than blood, e. g. water, are used. Such other
fluids would rather require as much free space in the outlet
chamber in the direct vicinity of the filter membrane as
possible.
[0055] In another preferred embodiment, at least 50%, preferably at
least 75%, more preferably at least 90%, and most preferably at
least 95% of the surface area of the second side of said filter
membrane is covered.
[0056] In a more preferred embodiment, the second side of the
membrane is in contact with a substantially flat substrate, wherein
said flat substrate is preferably part of the sampling
compartment.
[0057] The term "substantially flat" comprises surfaces which may
be completely flat, i.e. without any elevations or indentations in
the range of about 5-1000 .mu.m, but also surfaces, wherein at
least 80%, preferably at least 90%, more preferably at least 95%
are flat and also surfaces with elevations or indentations of less
than 1 mm height. The term also encompasses structures comprising
more than one flat area arranged in an angle or a curved, e.g.,
convex or concave configuration, laying flat on the filter and
preferably relates to material which is adapted to lay flat on or
against the second side of the filter. In other words, the dead
space between filter membrane and the supporting and draining flat
substrate should not exceed 5 .mu.l per cm.sup.2 filter membrane
surface, therefore most of the membrane is preferably in contact
with the substrate.
[0058] This preferred embodiment takes into account that small
channels in the blood filter leading to a place where the plasma or
serum can be collected may to a certain extent promote the yield of
serum or plasma. If present, said channels preferably lead to an
outlet comprised in said sampling compartment. However, a further
surprising effect of the present invention is that generally the
larger the part of the filter membrane being in contact with said
substantially flat surface, the better is the yield of serum or
plasma.
[0059] In a preferred embodiment of the methods or the filter of
the invention, the blood filter further comprises a hydrophilic and
porous sheet arranged on the first side of said filter membrane in
said receiving compartment which is preferably covering said filter
membrane, wherein said porous sheet is preferably made of fibrous
material.
[0060] Suitable sheets are filter paper (such as used in teabags),
nonwoven fabrics (sheet or web structures bonded together by
entangling fiber or filaments) made of cellulose or plastic which
is made hydrophilic.
[0061] A hydrophilic and porous sheet according to the invention
serves for rapidly and more evenly distributing the blood to be
filtered over preferably the whole surface of the filter membrane.
Furthermore, said sheet prevents that mixtures of gas with serum or
plasma are obtained from the filtering process which would pose the
potential danger of obtaining unwanted foams. The sheet is arranged
on the first side of said filter membrane facing the receiving
compartment, wherein the filter membrane may be in direct contact
with said sheet or be arranged in a distance of up to 1.5 mm, such
as 0.5, 0.75, 1 or 1.25 mm. Suitable pore sizes are e. g. pore
sizes larger than 20 .mu.m, such as 50 .mu.m, 100 .mu.m, 200 .mu.m,
500 .mu.m or 1000 .mu.m. These pore sizes enable for the rapid
suction of the blood into the thin layer due to capillary forces
and its subsequent entry into the filter membrane due to the
increased pressure resulting from the compressed gas. Furthermore,
a part of the cellular constituents of the blood may already be
removed from the sample at this stage. The sheet is preferably
between 0.1 and 1 mm thin. The term "covering said filter membrane"
in the context of this aspect of the invention describes the
surface of the sheet as either as large as that of the filter
membrane, but also smaller or bigger than the filter membrane. Most
common would be surfaces which are at least 80%, preferably at
least 90%, more preferably at least 95% as large as that of the
filter membrane. Equally preferred are sheets which are up to 10%
larger than the filter membrane.
[0062] In a preferred embodiment of the first and third aspect of
the invention, said receiving compartment comprises a sample
insertion means. Said sample insertion means is e. g. part of the
preferred embodiment as depicted in FIGS. 1, 3, 5, 7, 9 and 10.
Said sample insertion means enables for the introduction of the
blood sample to be filtered into the receiving compartment.
[0063] In a more preferred embodiment, said sample insertion means
comprises a one-way valve, especially for filters depicted in FIGS.
1, 3, 5, 7, 9 and 10. A one-way valve is especially preferable if
the blood is introduced with a means which is subsequently removed
such as a syringe. In order to prevent that the internal pressure
within the receiving compartment is relieved through said sample
insertion means, a one-way valve prevents that gas and/or blood
leaks out from said sample insertion means rather than is passed
through said filter membrane.
[0064] In another preferred embodiment, said sample insertion means
comprises a luer-taper. This embodiment can be applied if the blood
is introduced with a means which is not subsequently removed, such
as a syringe. In this regard, the plunger of the syringe will
withstand the pressure of about 5-20 kPa because the plunger is
stucked in the tube due to the clamping force of the syringe
required to be overcome for moving the plunger. This will be the
case with most syringes holding a volume up to 10 ml.
[0065] It is preferred that the syringe comprises a means to lock
the plunger at the position it has reached after the blood has been
introduced into the receiving chamber. This is useful in the case,
that the plunger of the syringe is sliding very easily.
[0066] In another more preferred embodiment of the blood filter of
the invention, said receiving compartment comprises a syringe.
[0067] In this preferred embodiment of the blood filter of the
invention, said hollow space of said receiving compartment is for
the most part formed by a syringe, whereas only a small part is
formed by the space in the immediate vicinity of the first side of
the filter membrane. In this embodiment, said syringe comprises the
volume of blood to be filtered as well as the appropriate amount of
gas, such as air. For filtering the blood, the plunger of the
syringe is pressed and the volume of the syringe is reduced by the
volume of the blood sample to be filtered. After that, the plunger
of the syringe is preferably fixed at that position in order to
ensure that the pressure is maintained and that no overpressure is
applied.
[0068] In a preferred embodiment of the methods and the blood
filter of the invention, said sampling compartment comprises an
outlet, preferably a universal adaptor.
[0069] Said outlet is preferably compatible with commonly used
blood filters for further processing of the serum or plasma, such
as detection devices, small vessels or short outlets. A universal
adaptor enables for the collection of serum or plasma in more than
one different devices for further processing of the serum or
plasma.
[0070] In another preferred embodiment, the blood filter is
disposable.
[0071] In another preferred embodiment of the methods and the blood
filter of the invention, said receiving compartment comprises a
nozzle arranged at said sample insertion means. Said nozzle reaches
into the hollow space formed by said receiving compartment and may
be of a certain length. It serves for conducting the blood sample
in the direction of the filter membrane. Accordingly preferred
nozzles may reach into said hollow space up to a mm or a few mm in
front of said filter membrane. The latter preferred embodiment is
especially suitable if the distance between said sample insertion
means and said filter membrane is large such as at least 1 cm and
if the volume of blood sample to be filtered is small, such as up
to 500 .mu.l using a membrane surface of about 5 cm.sup.2.
[0072] In a more preferred embodiment, the nozzle is attached to a
disc, wherein said disc is arranged on top of said first side of
the filter membrane. Said disc is not in direct contact with said
first side of said filter membrane but arranged in a distance of
between 0.1 mm and 1.5 mm. Said distance may develop primal after
pressure is applied. Said disc does not span the whole hollow space
but leaves at least one gap for pressure balance. The principle
underlying this embodiment of the blood filter and method of the
invention is that blood led through the nozzle towards the filter
membrane is guided by the disc to be evenly distributed on the
filter membrane.
[0073] In another preferred embodiment of the methods and the blood
filter of the invention, the receiving compartment and/or the first
side of the filter membrane further comprises at least one
substance which can immobilize at least one cellular constituent of
blood, such as erythrocytes, leukocytes or thrombocytes. Suitable
substances in this regard are e. g. antibodies specifically binding
to at least one of the above cell types, such as e. g. anti-human
erythrocyte antibodies. Said substances may be present in the form
of a powder, attached within said receiving compartment or on said
first side of the filter membrane or attached on a tissue comprised
in the receiving compartment. Exemplary tissues are Leukogard,
distributed by Pall, or LG6. Those leukocyte filters may contain
polyester wool which surface is treated in a way, so that
leukocytes adhere immediately on the wool. Alternatively or in
addition, the filters may comprise antibodies to erythrocytes.
Further alternatively, the receiving compartment may comprise a
powder comprising heterophilic antibodies which agglutinate
erythrocytes. Other suitable compounds for agglutination of
erythrocytes may be obtained from yeast cells of Histoplasma
capsulatum or from pyrogenic silica, wheat germ agglutinin, lectin
from seeds of bitter gourd, balsam pear, or Momordica charantia or
other lectins.
[0074] The present invention further relates to the use of the
filter of the invention for filtering blood to produce serum or
plasma.
[0075] In a preferred embodiment of the method of the invention,
the blood filter of step a. is the blood filter according to the
invention.
[0076] The present invention furthermore relates to a kit
comprising a blood filter for the production of plasma or serum
from a blood sample and a syringe. The blood filter comprises a
filter membrane having opposite first and second sides, a receiving
compartment defining a hollow space for receiving a blood sample to
be filtered from said syringe, and a sampling compartment being
arranged on said second side of said filter membrane. Said
receiving compartment has at least one opening covered with said
filter membrane, wherein said first side is facing the receiving
compartment, and wherein the hollow space of said receiving
compartment has a first volume. The syringe is adapted to receive a
predetermined second volume of blood sample, wherein the first
volume is 3 to 20 times larger than the second volume.
[0077] The present invention furthermore relates to a kit
comprising a blood filter for the production of plasma or serum
from a blood sample and a syringe. The blood filter comprises a
filter membrane having opposite first and second sides, a receiving
compartment defining a hollow space for receiving a blood sample to
be filtered from said syringe, and a sampling compartment being
arranged on said second side of said filter membrane. Said
receiving compartment has at least one opening covered with said
filter membrane, wherein said first side is facing the receiving
compartment, and wherein the hollow space of said receiving
compartment has a first volume. The syringe is adapted to receive a
predetermined second volume of blood sample and a predetermined
third volume of a gas. Furthermore, the syringe is adapted to
compress the third volume by between 1/20 to 1/5 of the third
volume
[0078] According to a preferred embodiment, the first volume of
said hollow space or the sum of said first and third volume is at
least 0.3 ml.
[0079] The receiving compartment is preferably made from a material
that is adapted to withstand an internal pressure of at least 7
kPa, more preferably at least 18 kPa, and even more preferably at
least 35 kPa without substantial deformation.
[0080] Accordingly, the receiving compartment is preferably made
from a substantially inelastic and/or rigid material.
[0081] According to a preferred embodiment, at least 50%,
preferably at least 75%, more preferably at least 90%, and most
preferably at least 95% of the surface area of the second side of
said filter membrane is covered. It is preferred that the second
side of the membrane is in contact with a substantially flat
substrate, wherein said flat substrate is preferably part of the
sampling compartment.
[0082] According to a preferred embodiment, the filter further
comprises a hydrophilic and porous sheet arranged on the first side
of said filter membrane in said receiving compartment which is
preferably covering said filter membrane, wherein said porous sheet
is preferably made of fibrous material.
[0083] According to a preferred embodiment, said receiving
compartment comprises a sample insertion means, which is preferably
a one-way-valve. The sampling compartment preferably comprises at
least one outlet, preferably a universal adaptor.
[0084] It is preferred that the syringe comprises a plunger and a
first stop for the plunger of the syringe to stop the plunger
during suction or pulling. This minimizes the risk of the plunger
being pulled out of the syringe, which in the worst case could lead
to spilling the blood sample all over. Furthermore, the first stop
can be utilized to determine the third volume. The user may, for
example, be told (e.g. by means of an instruction leaflet) to
uptake a certain second volume of blood such as 0.5 to 2 ml and to
fill up the syringe with a gas, e.g. with air, until the plunger is
stopped by the first stop. Thus, the third volume is defined as the
inner volume of the syringe minus the second volume loaded with
blood.
[0085] In addition, the syringe preferably comprises a second stop
for the plunger of the syringe to stop the plunger during pushing
downwards the plunger within the syringe in order to limit the
compression of the third volume. Accordingly, the gas occupying the
third volume is compressed by a specific predetermined amount,
which results in a predetermined pressure within the third volume
which acts onto the blood sample during filtering. Preferably, the
first and second stops are arranged such that the third volume is
compressed by between 1/20 to 1/5 of the third volume. If standard
pressure was present before compression, a pressure of between 1.05
bar and 1.2 bar is achieved, which is sufficient to filter the
blood while at the same time sufficiently small to avoid
hemolysis.
[0086] It is further preferred that the syringe comprises means to
arrest the plunger thereof in a predetermined position, preferably
in a position after compression of the thirs volume. Thus, a user
may compress the gas inside the syringe by pressing down the
plunger and then arrest the plunger in the preferred position.
[0087] The various components of the kit may be packaged in one or
more containers.
[0088] The present invention further relates to the use of the kit
described above for filtering blood to produce serum or plasma.
[0089] The present invention furthermore relates to a blood filter
for the production of plasma or serum from a blood sample. The
filter comprises a filter membrane having opposite first and second
sides and a receiving compartment defining a hollow space for
receiving a blood sample to be filtered, said receiving compartment
being arranged on said first side of the filter membrane. The
filter membrane rests on a seating, wherein at least 50% of the
surface of the second side of the filter membrane is in contact
with said seating, and wherein the seating comprises a plurality of
channels for collecting the filtered blood sample. The channels
preferably empty out into at least one outlet. According to a
preferred embodiment, at least 75%, preferably at least 90% of the
surface of the second side of the filter membrane is in contact
with said seating.
[0090] It is preferred that the seating is convex having a radius
of curvature between 30 and 150 mm, preferably between 60 and 100
mm (analogous to a spherical cap). The convex seating may take
account of the elongation of the filter material after wetting in
order to avoid wrinkle formation. Surprisingly, it has been found
that a convex seating or pressure plate increases the filter
efficiency in comparison with a substantially flat seating or
pressure plate. The convex curvature of the seating inter alia
improves the ability of the channels to collect the filtered blood
sample and in particular to guide the collected blood sample
towards the outlet(s). For this purpose, it is particularly
advantageous that the channels are arranged in a grid or web-like
structure. Preferably, the ratio of the relative amount of surface
comprising channels to the amount of channel-free surface is
essentially constant (on a scale of cm.sup.2) over, preferably the
major area of, the surfaces facing the second side of the filter.
Preferably, all or substantially all points with maximum distance
to the closest or nearest channel have about the same maximum
distance. Furthermore, the total length of all channels should be
minimal. Furthermore, there may also be a channeling effect on or
within the second side of the filter membrane directed in a
direction roughly perpendicular to the filtration flow between
first and second side of the filter membrane.
[0091] According to a preferred embodiment, the plurality of
channels cover between 0.5 and 15%, preferably between 0.5 and 9%
of the surface of the seating. The skilled person will understand
that the channels are preferably equally distributed over the
seating surface to improve the coverage. It is also preferred that
two adjacent channels are not further than about 10 mm apart from
each other to ensure that blood reaching the seating surface
between two channels is collected by one of the channels.
[0092] According to a preferred embodiment, the plurality of
channels forms a sampling compartment having a volume in the range
between 0.06 mm.sup.3 and 3.5 mm.sup.3, preferably between 0.06
mm.sup.3 and 2 mm.sup.3 per cm.sup.2 of the filter surface.
[0093] In the following, the invention is further described on the
examples of certain preferred embodiments with reference to the
figures. It is to be understood that the figures not only exemplify
the blood filter of the invention but also serve to describe the
methods according to the invention. Each feature mentioned herein
below can equally be adapted and applied to the methods of the
invention at the appropriate place, which is immediately clear to
the skilled person.
[0094] The figures show:
[0095] FIG. 1: a sectional view of a preferred embodiment of the
blood filter according to the invention with a receiving
compartment.
[0096] FIG. 2: a sectional view of a preferred embodiment of the
blood filter according to the invention with a receiving
compartment comprising a syringe.
[0097] FIG. 3: a sectional view of a preferred embodiment of the
blood filter according to the invention with a receiving
compartment, wherein the blood filter comprises a hydrophilic and
porous sheet on the first side of the filter membrane.
[0098] FIG. 4: a sectional view of a preferred embodiment of the
blood filter according to the invention with a receiving
compartment comprising a syringe, wherein the blood filter
comprises a hydrophilic and porous sheet on the first side of the
filter membrane.
[0099] FIG. 5: a sectional view of a preferred embodiment of the
blood filter according to the invention with a receiving
compartment, wherein at least a part of the second side of the
filter membrane is covered.
[0100] FIG. 6: a sectional view of a preferred embodiment of the
blood filter according to the invention with a receiving
compartment comprising a syringe, wherein at least a part of the
second side of the filter membrane is covered.
[0101] FIG. 7: a sectional view of a preferred embodiment of the
blood filter according to the invention with a receiving
compartment, wherein the blood filter comprises a hydrophilic and
porous sheet on the first side of the filter membrane and wherein
at least a part of the second side of the filter membrane is
covered.
[0102] FIG. 8: a sectional view of a preferred embodiment of the
blood filter according to the invention with a receiving
compartment comprising a syringe, wherein the blood filter
comprises a hydrophilic and porous sheet on the first side of the
filter membrane and wherein at least a part of the second side of
the filter membrane is covered.
[0103] FIG. 9: a sectional view of a preferred embodiment of the
blood filter according to the invention with a receiving
compartment. The blood filter further comprises a nozzle of
variable length.
[0104] FIG. 10: a sectional view of a preferred embodiment of the
blood filter according to the invention with a receiving
compartment. The blood filter further comprises a nozzle and a disc
attached to the lower end of the nozzle.
[0105] FIG. 11: exemplary outlets or adaptors.
[0106] FIG. 12: a sectional view of a preferred embodiment of the
syringe to be used with the filter according to the invention with
stop mechanisms depicted
[0107] The operating position for the filters according to the
present invention, as shown in FIGS. 1-10 is preferably upright
with the outlet facing downwards. The deviation of the upright
position should not exceed 45 degrees.
[0108] A preferred embodiment of the blood filter according to the
invention as depicted in FIG. 1 comprises a filter membrane 6
having opposite first and second sides, a receiving compartment 2
defining a hollow space and being arranged on the first side of the
filter membrane as well as a sampling compartment 10 arranged on
the second side of the filter membrane. The blood 1 to be filtered
is introduced by a syringe which is, preferably only, filled with
blood and does not or essentially not comprise any gas such as air
in its inner space. The syringe is connected to a sample insertion
means 3 comprised in the receiving compartment 2. By pressing down
the plunger of the syringe, the blood 1 enters the receiving
compartment 2 which results in the gas contained in said receiving
compartment being compressed which creates a pressure within said
receiving chamber. This pressure forces the blood against, into
and/or through the filter membrane 6, where, depending on whether
the blood has been treated with anticoagulants, solid blood
components such as red and white blood cells and optionally
thrombocytes are retained, whereas the liquid part of the blood, i.
e. serum or plasma, is forced through the filter and enters the
sampling compartment 10. The serum or plasma can be collected by
having it pass through the outlet 12 for further use.
[0109] In this and the other preferred embodiments exemplified in
the figures, the receiving compartment 2 is preferably made from a
material that is adapted to withstand an internal pressure of at
least 7 kPa, preferably at least 18 kPa, without substantial
deformation. This means that, more preferably, said receiving
compartment is made from a substantially inelastic and/or rigid
material.
[0110] The blood filter according to the invention as depicted in
FIG. 2 comprises a filter membrane 6 having opposite first and
second sides, a receiving compartment 2', 2'' defining a hollow
space, wherein said receiving compartment is in part 2' formed by a
syringe, and a sampling compartment 10 arranged on the second side
of the filter membrane. In this embodiment, the major part of the
hollow space is formed by the syringe comprising the blood 1 to be
filtered and a volume of gas 2' under atmospheric pressure which is
between 3 and 20 times larger than the volume of blood 1 used to
operate the filter. The syringe is removable from the remaining
receiving compartment 2'' which is especially preferable in order
to fill it with the blood to be filtered and a volume of gas as
defined above. The thus filled syringe is attached to the remaining
receiving compartment 2'' via the connector 4 to complete said
receiving compartment. By pressing down the plunger of the syringe,
the blood 1 is driven to the part of the receiving compartment 2''
in the direct vicinity of the filter membrane. This results in the
gas contained in the receiving compartment 2'' being driven out
through the filter membrane and being replaced by blood to be
filtered. The gas 2' in the syringe above the blood 1 is compressed
because the plunger of the syringe is pressed down for at least
1/20 of the gas volume further after the point of equal pressure
inside and outside of the filter. The following processes are
similar to those described for FIG. 1. This means that the pressure
created forces the blood into the filter membrane 6, where,
depending on whether the blood has been treated with
anticoagulants, solid blood components such as red and white blood
cells and optionally at least a part of the thrombocytes are
retained, whereas the liquid part of the blood, i. e. serum or
plasma, is forced through the filter and enters the sampling
compartment 10. The serum or plasma can be collected by having it
pass through the outlet 12 for further use.
[0111] In all embodiments of the present invention, the volume of
gas or air particularly serves as an elastic buffer and/or pressure
reservoir for buffering the pressure applied by the user in order
to avoid destruction of erythrocytes by application of too high
pressures and for storing and transmitting the pressure applied by
the user, e.g. by pushing the plunger, to force or drive the blood
sample against the filter membrane.
[0112] In general, same reference numerals refer to identical or
closely similar features of the blood filter according to the
invention. All embodiments closely correspond apart from the
receiving compartment 2 being established in the blood filter only
as shown in, e.g., FIGS. 1, 3, 5, 7, 9, and 10 and being
established in part 2'' in the blood filter and in part 2' in the
syringe in, e.g., FIGS. 2, 4, 6, and 8.
[0113] In general, the blood filter according to the present
invention comprises a receiving compartment 2; 2'' and a sampling
compartment 10 separated by a filter membrane 6 and defined by a
housing, preferably a housing comprising two parts one of which
defines, preferably together with the filter membrane 6, the
receiving compartment 2; 2'' the other one of which defined,
preferably together with the filter membrane 6, the sampling
compartment 10. Preferably, the parts of the housing are connected
with one another at a sealed connector area, preferably defined be
means of a snap fit or thread connection. Preferably, said
connector area is also adapted to sealingly hold or engage the
filter membrane for separating the receiving and sampling
compartment.
[0114] According to a preferred additional and alternative
embodiment (not shown), the blood filter and preferably the syringe
comprises indicators suitable for conveying information to the user
about the amount of blood to be inserted into the syringe and/or
the blood filter as well as about the amount or way of travel the
plunger of the syringe is to be pushed down to suitably insert the
required volume of blood into the blood filter and to suitably
build up the required pressure. Alternatively and/or additionally
such indicators can include or can be replaced by means which limit
the way of travel of the plunger accordingly in one and/or two
directions to safeguard proper application of the method and use of
the device/kit.
[0115] The blood filter according to the invention as depicted in
FIG. 3 comprises a filter membrane 6 having opposite first and
second sides, a receiving compartment 2 defining a hollow space and
a sampling compartment 10 arranged on the second side of the filter
membrane. The blood filter further comprises a hydrophilic and
porous sheet 8 arranged on the first side of the filter membrane 6.
In this regard, it is preferred that at least a part of the sheet
is in direct contact with the filter membrane 6. This arrangement
enables for the rapid and even distribution of the blood to be
filtered throughout the filter membrane through capillary
force.
[0116] FIG. 4 depicts a blood filter according to the invention
comprising a filter membrane 6 having opposite first and second
sides, a receiving compartment 2 defining a hollow space, wherein
said receiving compartment comprises a syringe, and a sampling
compartment 10 arranged on the second side of the filter membrane.
The blood filter further comprises a hydrophilic an porous sheet 8
arranged on the first side of the filter membrane as described for
FIG. 3.
[0117] The blood filter according to the invention as depicted in
FIG. 5 comprises a filter membrane 6 having opposite first and
second sides, a receiving compartment 2 defining a hollow space and
a sampling compartment 10 arranged on the second side of the filter
membrane. In this preferred embodiment of the invention, at least
50%, preferably at least 75%, more preferably at least 90% and most
preferably at least 95% or the surface area of the second side of
the filter membrane 6, i. e. the side which points to the sampling
compartment, is in contact with a substantially flat substrate
which is part of the sampling compartment 10. The sampling
compartment according to this embodiment only comprises a small
hollow space which may be formed either by thin channels arranged
on said substantially flat substrate and/or solely by the space
near the outlet 12 which is not in contact with said substrate.
[0118] In this preferred embodiment, the above described contact
between the filter membrane 6 and the substrate which is part of
the sampling compartment 10, preferably forms at least a part of
the boundary of the sampling compartment promotes the accumulation
of serum or plasma in the vicinity of the outlet 12.
[0119] An embodiment similar to that depicted in FIG. 5, i. e. with
the special feature of the filter membrane 6 being in contact with
said substrate is also depicted in FIG. 6. In this embodiment, a
syringe is comprised in the receiving compartment 2 as described e.
g. for FIG. 2.
[0120] The preferred embodiment depicted in FIG. 7 is a combination
of the embodiments of FIGS. 3 and 5. This means that the blood
filter according to the invention as depicted in FIG. 1 further
comprises a hydrophilic and porous sheet 8 arranged on the first
side of the filter membrane as described for FIG. 3. Furthermore,
in this preferred embodiment of the invention, at least 50%,
preferably at least 75%, more preferably at least 90% and most
preferably at least 95% or the surface area of the second side of
the filter membrane 6, i. e. the side which points to the sampling
compartment 10, is in contact with a substantially flat substrate
which is part of the sampling compartment as described for FIG.
5.
[0121] In FIG. 8, the embodiments described for FIGS. 4 and 6 are
combined. This means that the blood filter according to the
invention as depicted in FIG. 2 further comprises a hydrophilic and
porous sheet 8 arranged on the first side of the filter membrane as
described for FIG. 4. Furthermore, in this preferred embodiment of
the invention, at least 50%, preferably at least 75%, more
preferably at least 90% and most preferably at least 95% or the
surface area of the second side of the filter membrane 6, i. e. the
side which points to the sampling compartment, is in contact with a
substantially flat substrate which is part of the sampling
compartment 10 as described for FIG. 6.
[0122] The blood filter depicted in FIG. 9 comprises the features
as depicted and described in FIG. 1. The blood filter further
comprises a nozzle 5 which reaches into the hollow space of the
receiving compartment 2 and points towards the filter membrane 6.
The nozzle can be of variable length, e. g. depending on the height
of the receiving compartment 2 and/or on the volume of blood 1 to
be filtered. In this embodiment, the blood can be directly applied
to the filter membrane 6 through the nozzle without the danger of
sticking to the side walls of the receiving compartment. This is
especially suitable for small volumes of blood. The blood filter of
this embodiment preferably further comprises a hydrophilic and
porous sheet 8 arranged on the first side of the filter membrane as
described for FIG. 3. It is even more preferred that, alternatively
or in addition, at least 50%, preferably at least 75%, more
preferably at least 90% and most preferably at least 95% or the
surface area of the second side of the filter membrane 6, i. e. the
side which points to the sampling compartment 10, is in contact
with a substantially flat substrate which is part of the sampling
compartment as described for FIG. 5.
[0123] The preferred embodiment as depicted in FIG. 10 is based on
the blood filter of FIG. 9. The blood filter further comprises a
disc 7 attached at the lower end of the nozzle 5 leaving an outlet
for the blood lead through the nozzle. Said disc is constructed
such that it does not completely span the blood filter in
horizontal direction but leaves a gap 9 between the side boundary
of the receiving compartment 2 and the disc. The principle
underlying this embodiment of the blood filter of the invention is
that blood lead through the nozzle towards the filter membrane 6 is
guided to be evenly distributed on the filter membrane. The
necessary pressure for filtration can still be created since the
space underneath the disc is in communication with that above
through the gap. The blood filter of this embodiment preferably
further comprises a hydrophilic and porous sheet 8 arranged on the
first side of the filter membrane as described for FIG. 3. It is
even more preferred that, alternatively or in addition, at least
50%, preferably at least 75%, more preferably at least 90% and most
preferably at least 95% or the surface area of the second side of
the filter membrane 6, i. e. the side which points to the sampling
compartment, is in contact with a substantially flat substrate
which is part of the sampling compartment as described for FIG.
5.
[0124] FIG. 12A shows a preferred syringe to be used in combination
with the inventive method and/or kit. In the situation shown in
FIG. 12A, a predetermined second volume of blood 1 has already been
inserted into the syringe. By pulling the plunger in the direction
indicated by the arrow, a gas such as air fills a third volume 2'.
This process can be continued until the plunger reaches a first
stop 13, which is designed to prevent the plunger of being pulled
out of the syringe (see FIG. 12B). The next step is to press the
plunger downwards from the position shown in FIG. 12B in order to
compress the third volume 2' until a predetermined pressure
increase is achieved. In order to limit the compression of the
third volume 2' a second stop 14 is provided, which is designed to
stop the movement of the plunger during pushing downwards (see FIG.
12C). As shown in the sequence of FIGS. 12A-C, the second stop 14
will come into effect only after pulling the plunger all the way up
towards the first stop. Thus, a user will be easily guided through
the method steps according to the present invention: The user pulls
a certain amount of blood into the syringe, then fills the
remaining volume of the syringe with a gas such as air until the
plunger is stopped by the first stop. Subsequently, the user simply
has to push the plunger downwards until the movement of the plunger
is again stopped, this time by the second stop. Preferably, as
depicted, stop 1 is realized by means of a mechanical or fixed
stopping shoulder and/or stop 2 is realized as a biased or snapfit
member.
[0125] The blood filter according to the present invention is of
particular advantage--in addition to the advantages already
discussed in the preceding description--in that it allows the
provision of a simple, easy to manufacture blood filter and a
corresponding kit and method for filtering blood which can suitably
be used also by untrained staff in a fast, easy and reliably way.
The invention allows a ready to use provision of a blood filter and
corresponding conductance of the method independent on place and
time. Also very low amounts (volume) of blood can be filtered in a
reliably and reproducible manner. This is of particular advantage
when sampling blood of new born babies. The device can be easily
stored such that it is kept clean and sterile and thus ready to
use. Further advantages of the present invention will become
apparent form the further specification.
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