U.S. patent application number 10/264662 was filed with the patent office on 2003-02-13 for vacuum loaded test strip with stop junction and bypass channel.
Invention is credited to Chow, Herbert, Hartmann, Christa, Shartle, Robert Justice.
Application Number | 20030031594 10/264662 |
Document ID | / |
Family ID | 26787520 |
Filed Date | 2003-02-13 |
United States Patent
Application |
20030031594 |
Kind Code |
A1 |
Shartle, Robert Justice ; et
al. |
February 13, 2003 |
Vacuum loaded test strip with stop junction and bypass channel
Abstract
A fluidic medical diagnostic device permits measurement of
analyte concentration or a property of a biological fluid,
particularly the coagulation time of blood. The device has at one
end a sample port for introducing a sample and at the other end a
bladder for drawing the sample to a measurement area. A channel
carries the sample from the sample port to the measurement area,
and a stop junction, between the measurement area and bladder,
halts the sample flow. The desired measurement can be made by
placing the device into a meter which measures a physical property
of the sample--typically, optical transmittance--after it has
interacted with a reagent in the measurement area.
Inventors: |
Shartle, Robert Justice;
(Livermore, CA) ; Chow, Herbert; (Redwood City,
CA) ; Hartmann, Christa; (Oakland, CA) |
Correspondence
Address: |
BOZICEVIC, FIELD & FRANCIS LLP
200 MIDDLEFIELD RD
SUITE 200
MENLO PARK
CA
94025
US
|
Family ID: |
26787520 |
Appl. No.: |
10/264662 |
Filed: |
October 3, 2002 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10264662 |
Oct 3, 2002 |
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09333765 |
Jun 15, 1999 |
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60093421 |
Jul 20, 1998 |
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Current U.S.
Class: |
422/400 ;
436/165; 436/169; 436/170 |
Current CPC
Class: |
G01N 33/5304 20130101;
B01L 2300/0864 20130101; B01L 2300/0822 20130101; B01L 2300/0825
20130101; B01L 2400/0406 20130101; B01L 2200/12 20130101; B01L
2400/0481 20130101; Y10T 436/112499 20150115; B01L 2300/087
20130101; G01N 33/4905 20130101; G01N 33/558 20130101; B01L
3/502738 20130101; Y10T 436/25375 20150115; G01N 2333/96447
20130101; G01N 21/8483 20130101; B01L 3/502723 20130101; B01L
2300/0887 20130101; B01L 3/5027 20130101; B01L 2300/0681 20130101;
G01N 33/54386 20130101; G01N 33/525 20130101; G01N 2333/7454
20130101; B01L 2400/0688 20130101; B01L 2200/0621 20130101 |
Class at
Publication: |
422/58 ; 422/56;
422/55; 436/165; 436/169; 436/170 |
International
Class: |
G01N 031/22 |
Claims
We claim:
1. A fluidic diagnostic device for measuring an analyte
concentration or property of a biological fluid, comprising a first
layer and second layer, at least one of which has a resilient
region over at least a part of its area, separated by an
intermediate layer, in which cutouts in the intermediate layer
form, with the first and second layers, a) a sample port for
introducing a sample of the biological fluid into the device; b) a
first measurement area, in which a physical parameter of the sample
is measured and related to the analyte concentration or property of
the fluid; c) a first channel, having a first end and a second end,
to provide a fluidic path from the sample port at the first end
through the first measurement area; d) a first bladder, at the
second end of the first channel, comprising at least a part of the
resilient region in at least the first or second layer and having a
volume that is at least about equal to the combined volume of the
first measurement area and first channel; and e) a first stop
junction in the first channel between the first measurement area
and first bladder that comprises a co-aligned through hole in the
first or second layer, the through hole overlaid with a third
layer.
2. The device of claim 1 in which the sample port comprises
co-aligned through holes in the first and intermediate layers.
3. The device of claim 1 in which the first stop junction further
comprises a second through hole aligned with the first through
hole, the second through hole being overlaid with a fourth
layer.
4. The device of claim 1, further comprising a bypass channel, to
provide an additional path from the first channel to the bladder,
without traversing the first measurement area and first stop
junction.
5. The device of claim 1 in which at least the first or second
layer is substantially transparent adjoining the first measurement
area, and the physical parameter that is measured is optical
transmission.
6. The device of claim 5 further comprising a reflective surface
adjoining the first measurement area.
7. The device of claim 1 in which the physical parameter of the
sample undergoes a change in the measurement area.
8. The device of claim 7 in which the first measurement area
contains a composition that facilitates blood clotting, the
biological fluid is whole blood, and the property being measured is
prothrombin time.
9. The device of claim 8 in which the composition comprises
thromboplastin.
10. The device of claim 1 further comprising a filter adjoining the
sample port for filtering the biological fluid being introduced
into the sample port.
11. The device of claim 10 in which the filter comprises an
anisotropic membrane.
12. The device of claim 11 in which the filter material is
polysulfone.
13. The device of claim 1 further comprising at least one
additional measurement area between the first measurement area and
the stop junction.
14. The device of claim 1 further comprising at least one alternate
fluidic path from the first channel to the bladder, each such
alternate path including a corresponding measurement area and stop
junction.
15. The device of claim 4 in which the first measurement area
contains a composition that facilitates blood clotting, the
biological fluid is whole blood, and the property being measured is
prothrombin time.
16. The device of claim 15 further comprising at least one
alternate fluidic path from the first channel to the bladder, each
such alternate path including a corresponding measurement area and
stop junction.
17. The device of claim 16 in which a first alternate path is to a
measurement area that overcomes the effect of an anticoagulant and
a second alternate path is to a measurement area that partially
overcomes the effect of an anticoagulant.
18. The device of claim 17 in which the measurement area in the
first alternate path comprises thromboplastin, bovine eluate, and
recombinant Factor VIIa and the measurement area in the second
alternate path comprises thromboplastin and bovine eluate.
19. The device of claim 13 further comprising at least one set of
channel, measurement area, and stop junction between the first stop
junction and first bladder and, adjoining the first bladder, an
additional bladder for each such set.
20. The device of claim 19 further comprising a bypass channel from
the first channel to the first bladder and an additional bypass
channel from the channel of each additional set to the
corresponding additional bladder.
21. A fluidic diagnostic device for measuring an analyte
concentration or property of a biological fluid, comprising a first
layer, which has a resilient region over at least a part of its
area, and a second layer, separated by an intermediate layer, in
which recesses in a first surface of the intermediate layer form,
with the first layer, a) a sample port for introducing a sample of
the biological fluid into the device; b) a measurement area, in
which the sample undergoes a change in a physical property that is
measured and related to the analyte concentration or property of
the fluid; c) a channel, having a first end and a second end, to
provide a fluidic path from the sample port at the first end
through the measurement area; and d) a bladder, at the second end
of the channel, comprising the resilient region in the first layer
and having a volume that is at least about equal to the combined
volume of the measurement area and channel; and a stop junction in
the channel between the measurement area and bladder that comprises
two passages substantially normal to the first surface of the
intermediate layer, each passage having a first end in fluid
communication with the channel and a second end in fluid
communication with a recess in a second surface of the intermediate
layer, which recess provides fluid communication between the second
ends of the passages.
Description
CROSS-REFERENCE TO PRIOR PROVISIONAL APPLICATION
[0001] This application claims the benefit of U.S. Provisional
Application No. 60/093,421, filed Jul. 20, 1998
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] This invention relates to a fluidic medical diagnostic
device for measuring the concentration of an analyte in or a
property of a biological fluid.
[0004] 2. Description of the Related Art
[0005] A variety of medical diagnostic procedures involve tests on
biological fluids, such as blood, urine, or. saliva, and are based
on a change in a physical characteristic of such a fluid or an
element of the fluid, such as blood serum. The characteristic can
be an electrical, magnetic, fluidic, or optical property. When
optical property is monitored, these procedures may make use of a
transparent or translucent device to contain the biological fluid
and a reagent. A change in light absorption of the fluid can be
related to an analyte concentration in, or property of, the fluid.
Typically, a light source is located adjacent to one surface of the
device and a detector is adjacent to the opposite surface. The
detector measures light transmitted through a fluid sample.
Alternatively, the light source and detector can be on the same
side of the device, in which case the detector measures light
scattered and/or reflected by the sample. Finally, a reflector may
be located at or adjacent to the opposite surface. A device of this
latter type, in which light is first transmitted through the sample
area, then reflected through a second time, is called a
"transflectance" device. References to "light" throughout this
specification and the appended claims should be understood to
include the infrared and ultraviolet spectra, as well as the
visible. References to "absorption" are meant to refer to the
reduction in intensity as a light beam passes through a medium;
thus, it encompasses both "true" absorption and scattering.
[0006] An example of a transparent test device is described in
Wells et al. W094/02850, published on Feb. 3, 1994. Their device
comprises a sealed housing, which is transparent or translucent,
impervious, and rigid or semi-rigid. An assay material is contained
within the housing, together with one or more assay reagents at
predetermined sites. The housing is opened and the sample
introduced just before conducting the assay. The combination of
assay reagents and analyte in the sample results in a change in
optical properties, such as color, of selected reagents at the end
of the assay. The results can be read visually or with an optical
instrument.
[0007] U.S. Pat. No. 3,620,676, issued on Nov. 16, 1971 to Davis,
discloses a calorimetric indicator for liquids. The indicator
includes a "half-bulb cavity", which is compressible. The bulb is
compressed and released to form a suction that draws fluid from a
source, through a half-tubular cavity that has an indicator
imprinted on its wall. The only controls on fluid flow into the
indicator are how much the bulb is compressed and how long the
indicator inlet is immersed in the source, while the bulb is
released.
[0008] U.S. Pat. No. 3,640,267, issued on Feb. 8, 1972 to Hurtig et
al., discloses a container for collecting samples of body fluid
that includes a chamber that has resilient, collapsible walls. The
walls are squeezed before the container inlet is placed into the
fluid being collected. When released, the walls are restored to
their uncollapsed condition, drawing fluid into and through the
inlet. As with the Davis device, discussed above, control of fluid
flow into the indicator is very limited.
[0009] U.S. Pat. No. 4,088,448, issued on May 9, 1978 to Lilja et
al., discloses a cuvette, which permits optical analysis of a
sample mixed with a reagent. The reagent is coated on the walls of
a cavity, which is then filled with a liquid sample. The sample
mixes with the reagent to cause an optically-detectable change.
[0010] A number of patents, discussed below, disclose devices for
diluting and/or analyzing biological fluid samples. These devices
include valve-like designs to control the flow of the sample.
[0011] U.S. Pat. No. 4,426,451, issued on Jan. 17, 1984 to
Columbus, discloses a multi-zone fluidic device that has
pressure-actuatable means for controlling the flow of fluid between
the zones. His device makes use of pressure balances on a liquid
meniscus at the interface between a first zone and a second zone
that has a different cross section. When both the first and second
zones are at atmospheric pressure, surface tension creates a back
pressure that stops the liquid meniscus from proceeding from the
first zone to the second. The configuration of this interface or
"stop junction" is such that the liquid flows into the second zone
only upon application of an externally generated pressure to the
liquid in the first zone that is sufficient to push the meniscus
into the second zone.
[0012] U.S. Pat. No. 4,868,129, issued on Sep. 19, 1989 to Gibbons
et al., discloses that the back pressure in a stop junction can be
overcome by hydrostatic pressure on the liquid in the first zone,
for example by having a column of fluid in the first zone.
[0013] U.S. Pat. No. 5,230,866, issued on Jul. 27, 1993 to Shartle
et al., discloses a fluidic device with multiple stop junctions in
which the surface tension-induced back pressure at the stop
junction is augmented; for example, by trapping and compressing gas
in the second zone. The compressed gas can then be vented before
applying additional hydrostatic pressure to the first zone to cause
fluid to flow into the second zone. By varying the back pressure of
multiple stop junctions in parallel, "rupture junctions" can be
formed, having lower maximum back pressure.
[0014] U.S. Pat. No. 5,472,603, issued on Dec. 5, 1995 to Schembri
(see also U.S. Pat. No. 5,627,041), discloses using centrifugal
force to overcome the back pressure in a stop junction. When flow
stops, the first zone is at atmospheric pressure plus a
centrifugally generated pressure that is less than the pressure
required to overcome the back pressure. The second zone is at
atmospheric pressure. To resume flow, additional centrifugal
pressure is applied to the first zone, overcoming the meniscus back
pressure. The second zone remains at atmospheric pressure.
[0015] European Pat. No. Application EP 0 803 288, of Naka et al.,
published on Oct. 29, 1997, discloses a device and method for
analyzing a sample that includes drawing the sample into the device
by suction, then reacting the sample with a reagent in an
analytical section. Analysis is done by optical or electrochemical
means. In alternate embodiments, there are multiple analytical
sections and/or a bypass channel. The flow among these sections is
balanced without using stop junctions.
[0016] U.S. Pat. No. 5,700,695, issued on Dec. 23, 1997 to
Yassinzadeh et al., discloses an apparatus for collecting and
manipulating a biological fluid that uses a "thermal pressure
chamber" to provide the driving force for moving the sample through
the apparatus.
[0017] U.S. Pat. No. 5,736,404, issued on Apr. 7, 1998, to
Yassinzadeh et al., discloses a method for determining the
coagulation time of a blood sample that involves causing an end of
the sample to oscillate within a passageway. The oscillating motion
is caused by alternately increasing and decreasing the pressure on
the sample.
SUMMARY OF THE INVENTION
[0018] The present invention provides a fluidic diagnostic device
for measuring an analyte concentration or property of a biological
fluid. The device comprises
[0019] a first layer and second layer at least one of which has a
resilient region over at least part of its area, separated by an
intermediate layer, in which cutouts in the intermediate layer
form, with the first and second layers,
[0020] a) a sample port for introducing a sample of the biological
fluid into the device;
[0021] b) a first measurement area, in which a physical parameter
of the sample is measured and related to the analyte concentration
or property of the fluid;
[0022] c) a first channel, having a first end and a second end, to
provide a fluidic path from the sample port at the first end
through the first measurement area;
[0023] d) a first bladder at the second end of the first channel,
comprising at least a part of the resilient region in at least the
first or second layer and having a volume that is at least about
equal to the combined volume of the first measurement area and
first channel; and
[0024] e) a first stop junction in the first channel between the
first measurement area and first bladder that comprises a
co-aligned through hole in at least the first or second layer, the
through hole being overlaid with a third layer.
[0025] In another embodiment, the device comprises
[0026] a first layer, which has a resilient region over at least a
part of its area, and a second layer, separated by an intermediate
layer, in which recesses in a first surface of the intermediate
layer form, with the first layer,
[0027] a) a sample port for introducing a sample of the biological
fluid into the device;
[0028] b) a measurement area, in which the sample undergoes a
change in a physical parameter that is measured and related to the
analyte concentration or property of the fluid;
[0029] c) a channel, having a first end and a second end, to
provide a fluidic path from the sample port at the first end
through the measurement area; and
[0030] d) a bladder, at the second end of the channel, comprising
at least a part of the resilient region in the first layer and
having a volume that is at least about equal to the combined volume
of the measurement area and channel; and
[0031] a stop junction in the channel between the measurement area
and bladder that comprises two passages substantially normal to the
first surface of the intermediate layer, each passage having a
first end in fluid communication with the channel and a second end
in fluid communication with a recess in a second surface of the
intermediate layer, which recess provides fluid communication
between the second ends of the passages.
[0032] The device is particularly well adapted for measuring
prothrombin time (PT time), with the biological fluid being whole
blood and the measurement area having a composition that catalyzes
the blood clotting cascade.
BRIEF DESCRIPTION OF THE DRAWINGS
[0033] FIG. 1 is a plan view of a device of the present
invention.
[0034] FIG. 2 is an exploded view of the device of FIG. 1.
[0035] FIG. 3 is a perspective view of the device of FIG. 1.
[0036] FIG. 4 is a schematic of a meter for use with a device of
this invention.
[0037] FIG. 4A depicts an alternative embodiment of an element of
the meter of FIG. 4.
[0038] FIG. 5 is a graph of data that is used to determine PT
time.
[0039] FIG. 6 is a plan view of an alternative embodiment of a
device of this invention.
[0040] FIGS. 6A, 6B, and 6C depict a time sequence during which a
sample is admitted to the device of FIG. 6.
[0041] FIG. 7 is a schematic of a device having multiple
measurement areas in parallel, multiple stop junctions in parallel,
and a single bladder.
[0042] FIG. 8 is a schematic of a device having multiple
measurement areas in series, with a single stop junction, a single
bladder, and a filter over the sample port.
[0043] FIG. 9 is a schematic of a device having multiple
measurement areas and multiple stop junctions arranged in an
alternating series, as well as multiple bladders.
[0044] FIG. 10 is a schematic of a device that includes multiple
measurement areas in parallel, a single bladder, and a single
bypass channel.
[0045] FIG. 11 is a schematic of a device having multiple
measurement areas in series, multiple stop junctions in series,
multiple-bladders in series, and multiple bypass channels.
[0046] FIG. 12 is an exploded view of an injection-molded device of
this invention.
[0047] FIG. 13 is a perspective view of the device of FIG. 12.
DETAILED DESCRIPTION OF THE INVENTION
[0048] This invention relates to a fluidic device for analyzing
biological fluid. The device is of the type that relates a physical
parameter of the fluid, or an element of the fluid, to an analyte
concentration in the fluid or to a property of the fluid. Although
a variety of physical parameters--e.g., electrical, magnetic,
fluidic, or optical--can form the basis for the measurement, a
change in optical parameters is a preferred basis, and the details
that follow refer to an optical device. The device includes a
sample application area; a bladder, to create a suction force to
draw the sample into the device; a measurement area, in which the
sample may undergo a change in an optical parameter, such as light
scattering; and a stop junction to precisely stop flow after
filling the measurement area.
[0049] Preferably, the device is substantially transparent over the
measurement area, so that the area can be illuminated by a light
source on one side and the transmitted light measured on the
opposite side. The measurement on the sample may be of a parameter
that is not changing, but typically the sample undergoes a change
in the measurement area, and the change in transmitted light is a
measure of the analyte or fluid property of interest.
Alternatively, light that is scattered from a fluid sample or light
that passes through the sample and is reflected back through a
second time (by a reflector on that opposite side) can be detected
by a detector on the same side as the light source.
[0050] This type of device is suitable for a variety of analytical
tests of biological fluids, such as determining biochemical or
hematological characteristics, or measuring the concentration in
such fluids of proteins, hormones, carbohydrates, lipids, drugs,
toxins, gases, electrolytes, etc. The procedures for performing
these tests have been described in the literature. Among the tests,
and where they are described, are the following:
[0051] (1) Chromogenic Factor XIIa Assay (and other clotting
factors as well): Rand, M. D. et al., Blood, 88, 3432 (1996).
[0052] (2) Factor X Assay: Bick, R. L. Disorders of Thrombosis and
Hemostasis: Clinical and Laboratory Practice. Chicago, ASCP Press,
1992.
[0053] (3) DRVVT (Dilute Russells Viper Venom Test): Exner, T. et
al., Blood Coag. Fibrinol., 1, 259 (1990)
[0054] (4) Immunonephelometric and Immunoturbidimetric Assays for
Proteins: Whicher, J. T., CRC Crit. Rev. Clin Lab Sci. 18:213
(1983).
[0055] (5) TPA Assay: Mann, K. G., et al., Blood, 76, 755, (1990).;
and Hartshorn, J. N. et al., Blood, 78, 833 (1991).
[0056] (6) APTT (Activated Partial Thromboplastin Time Assay):
Proctor, R. R. and Rapaport, S. I. Amer. J. Clin. Path, 36, 212
(1961); Brandt, J. T. and Triplett, D. A. Amer. J. Clin. Path., 76,
530 (1981); and Kelsey, P. R. Thromb. Haemost. 52, 172 (1984).
[0057] (7) HbA1c Assay (Glycosylated Hemoglobin Assay): Nicol, D.
J. et al., Clin. Chem. 29, 1694 (1983).
[0058] (8) Total Hemoglobin: Schneck et al., Clinical Chem., 32/33,
526 (1986); and U.S. Pat. No. 4,088,448.
[0059] (9) Factor Xa: Vinazzer, H., Proc. Symp. Dtsch. Ges. Klin.
Chem., 203 (1977), ed. By Witt, I
[0060] (10) Colorimetric Assay for Nitric Oxide: Schmidt, H. H., et
al., Biochemica, 2, 22 (1995).
[0061] The present device is particularly well suited for measuring
blood-clotting time--"prothrombin time" or "PT time"--and details
regarding such a device appear below. The modifications needed to
adapt the device for applications such as those listed above
require no more than routine experimentation.
[0062] FIG. 1 is a plan view of a device 10 of the present
invention. FIG. 2 is an exploded view and FIG. 3 a perspective view
of the device. Sample is applied to sample port 12 after bladder 14
has been compressed. Clearly, the region of layer 26 and/or layer
28 that adjoins the cutout for bladder 14 must be resilient, to
permit bladder 14 to be compressed. Polyester of about 0.1 mm
thickness has suitable resilience and springiness. Preferably, top
layer 26 has a thickness of about 0.125 mm, bottom layer 28 about
0.100 mm. When the bladder is released, suction draws sample
through channel 16 to measurement area 18, which preferably
contains a reagent 20. In order to ensure that measurement area 18
can be filled with sample, the volume of bladder 14 is preferably
at least about equal to the combined volume of channel 16 and
measurement area 18. If measurement area 18 is to be illuminated
from below, layer 28 must be transparent where it adjoins
measurement area 18. For a PT test, reagent 20 contains
thromboplastin that is free of bulking reagents normally found in
lyophilized reagents.
[0063] As shown in FIGS. 1, 2, and 3, stop junction 22 adjoins
bladder 14 and measurement area 18; however, a continuation of
channel 16 may be on either or both sides of stop junction 22,
separating the stop junction from measurement area 18 and/or
bladder 14. When the sample reaches stop junction 22, sample flow
stops. For PT measurements, it is important to stop the flow of
sample as it reaches that point to permit reproducible "rouleaux
formation"--the stacking of red blood cells--which is an important
step in monitoring blood clotting using the present invention. The
principle of operation of stop junctions is described in U.S. Pat.
No. 5,230,866, incorporated herein by reference.
[0064] As shown in FIG. 2, all the above elements are formed by
cutouts in intermediate layer 24, sandwiched between top layer 26
and bottom layer 28. Preferably, layer 24 is double-sided adhesive
tape. Stop junction 22 is formed by an additional cutout in layer
26 and/or 28, aligned with the cutout in layer 24 and sealed with
sealing layer 30 and/or 32. Preferably, as shown, the stop junction
comprises cutouts in both layers 26 and 28, with sealing layers 30
and 32. Each cutout for stop junction 22 is at least as wide as
channel 16. Also shown in FIG. 2 is an optional filter 12A to cover
sample port 12. The filter may separate out red blood cells from a
whole blood sample and/or may contain a reagent to interact with
the blood to provide additional information. A suitable filter
comprises an anisotropic membrane, preferably a polysulfone
membrane of the type available from Spectral Diagnostics, Inc.,
Toronto, Canada. Optional reflector 18A may be on, or adjacent to,
a surface of layer 26 and positioned over measurement area 18. If
the reflector is present, the device becomes a transflectance
device.
[0065] The method of using the strip of FIGS. 1, 2, and 3 can be
understood with reference to a schematic of the elements of a meter
shown in FIG. 4, which contemplates an automated meter.
Alternatively, manual operation is also possible. (In that case,
bladder 14 is manually depressed before sample is applied to sample
port 12, then released.) The first step the user performs is to
turn on the meter, thereby energizing strip detector 40, sample
detector 42, measurement system 44, and optional heater 46. The
second step is to insert the strip. Preferably, the strip is not
transparent over at least a part of its area, so that an inserted
strip will block the illumination by LED 40a of detector 40b. (More
preferably, the intermediate layer is formed of a non-transparent
material, so that background light does not enter measurement
system 44.) Detector 40b thereby senses that a strip has been
inserted and triggers bladder actuator 48 to compress bladder 14. A
meter display 50 then directs the user to apply a sample to sample
port 12 as the third and last step the user must perform to
initiate the measurement sequence. The empty sample port is
reflective. When a sample is introduced into the sample port, it
absorbs light from LED 42a and thereby reduces the light that is
reflected to detector 42b. That reduction in light, in turn,
signals actuator 48 to release bladder 14. The resultant suction in
channel 16 draws sample through measurement area 18 to stop
junction 22. Light from LED 44a passes through measurement area 18,
and detector 44b monitors the light transmitted through the sample
as it is clotting. When there are multiple measurement areas,
measurement system 44 includes an LED/detector pair (like 44a and
44b) for each measurement area. Analysis of the transmitted light
as a function of time (as described below) permits a calculation of
the PT time, which is displayed on the meter display 50.
Preferably, sample temperature is maintained at about 37.degree. C.
by heater 46.
[0066] As described above, the detector senses a sample in sample
port 12, simply by detecting a reduction in (specular) reflection
of a light signal that is emitted by 42a and detected by 42b.
However, that simple system cannot easily distinguish between a
whole blood sample and some other liquid (e.g., blood serum) placed
in the sample port in error or, even, an object (e.g., a finger)
that can approach sample port 12 and cause the system to
erroneously conclude that a proper sample has been applied. To
avoid this type of error, another embodiment measures diffuse
reflection from the sample port. This embodiment appears in FIG.
4A, which shows detector 42b positioned normal to the plane of
strip 10. With the arrangement shown in FIG. 4A, if a whole blood
sample has been applied to sample port 12, the signal detected by
42b increases abruptly, because of scattering in the blood sample,
then decreases, because of rouleaux formation (discussed below).
The detector system 42 is thus programmed to require that type of
signal before causing actuator 48 to release bladder 14. The delay
of several seconds in releasing bladder 14 does not substantially
affect the readings described below
[0067] FIG. 5 depicts a typical "clot signature" curve in which the
current from detector 44b is plotted as a function of time. Blood
is first detected in the measurement area by 44b at time 1. In the
time interval A, between points 1 and 2, the blood fills the
measurement area. The reduction in current during that time
interval is due to light scattered by red cells and is thus an
approximate measure of the hematocrit. At point 2, sample has
filled the measurement area and is at rest, its movement having
been stopped by the stop junction. The red cells begin to stack up
like coins (rouleaux formation). The rouleaux effect allows
increasing light transmission through the sample (and less
scattering) in the time interval between points 2 and 3. At point
3, clot formation ends rouleaux formation and transmission through
the sample reaches a maximum. The PT time can be calculated from
the interval B between points 1 and 3 or between 2 and 3.
Thereafter, blood changes state from liquid to a semi-solid gel,
with a corresponding reduction in light transmission. The reduction
in current C between the maximum 3 and endpoint 4 correlates with
fibrinogen in the sample.
[0068] The device pictured in FIG. 2 and described above is
preferably formed by laminating thermoplastic sheets 26 and 28 to a
thermoplastic intermediate layer 24 that has adhesive on both of
its surfaces. The cutouts that form the elements shown in FIG. 1
may be formed, for example, by laser- or die-cutting of layers 24,
26, and 28. Alternatively, the device can be formed of molded
plastic. Preferably, the surface of sheet 28 is hydrophilic. (Film
9962, available from 3M, St. Paul, Minn.) However, the surfaces do
not need to be hydrophilic, because the sample fluid will fill the
device without capillary forces. Thus, sheets 26 and 28 may be
untreated polyester or other thermoplastic sheet, well known in the
art. Similarly, since gravity is not involved in filling, the
device can be used in any orientation. Unlike capillary fill
devices that have vent holes through which sample could leak, the
present device vents through the sample port before sample is
applied, which means that the part of the strip that is first
inserted into the meter is without an opening, reducing the risk of
contamination.
[0069] FIG. 6 is a plan view of another embodiment of the device of
the present invention, in which the device includes a bypass
channel 52 that connects channel 16 with bladder 14. The function
and operation of the bypass channel can be understood by referring
to FIGS. 6A, 6B, and 6C which depict a time sequence during which a
sample is drawn into device 10 for the measurement.
[0070] FIG. 6A depicts the situation after a user has applied a
sample to the strip, while bladder 14 is compressed. This can be
accomplished by applying one or more drops of blood.
[0071] FIG. 6B depicts the situation after the bladder is
decompressed. The resulting reduced pressure in the inlet channel
16 draws the sample initially into the measurement area 18. When
the sample reaches stop junction 22, the sample encounters a back
pressure that causes it to stop and causes additional sample to be
drawn into the bypass channel.
[0072] FIG. 6C depicts the situation when a reading is taken.
Sample is isolated and at rest in measurement area 18. Excess
sample and/or air has been drawn into bypass channel 52.
[0073] The bypass channel of FIG. 6 provides an important
improvement over the operation of the "basic" strip of FIGS. 1-3.
In the basic strip, stop junction 22 stops the flow of sample after
it fills measurement area 18. As was discussed earlier, it is
important to stop the flow in order to facilitate rouleaux
formation. As was also discussed earlier, the stop junction
accomplishes the flow stoppage as a result of surface tension
acting on the meniscus at the leading edge of the fluid at an
abrupt change in cross section of the flow channel. In the basic
strip, the pressure on the bladder side of the stop junction
remains below atmospheric pressure while the pressure on the sample
side remains open to atmosphere. Thus, there is an ambient pressure
imbalance on the two sides. The greater the imbalance, the greater
the risk that the stop junction will leak and that sample will flow
through the stop junction, interfering with rouleaux formation,
and, consequently, providing inaccurate values of PT.
[0074] Bypass channel 52 minimizes that risk. The reduced pressure
on the bladder side of the stop junction draws sample into the
bypass channel (FIGS. 6B, 6C) until the ambient pressure is
equalized at atmospheric pressure on both sides of the stop
junction. Note that the (reduced) pressure on the bladder side is
relatively uncontrolled. The bypass channel 52, by enabling the
pressures on the two sides of the stop junction to equilibrate,
permits the use of larger bladders that have greater suction.
Larger bladders, in turn, provide more reliable operation of the
system.
[0075] FIG. 7 depicts an embodiment of the present invention in
which there are multiple (three are shown) measurement areas "in
parallel". That is to say that the channels 116P, 216P, and 316P
fill substantially simultaneously (assuming they have the same
dimensions). The situation depicted in FIG. 7, with channels and
measurement areas filled with blood, is achieved, as discussed
above, by applying sample to sample port 112 while bladder 114 is
compressed, then releasing bladder 114. As discussed above, the
first step is to apply sample to sample well 112 while bladder 114
is compressed. The second step is to release the bladder. Sample
flows to measurement areas 118P, 218P, and 318P, and flow stops
when sample reaches stop junctions, 122P, 222P, and 322P,
respectively. The optional second and third measurement areas may
contain, for example, reagents that neutralize the presence of
interferents (such as heparin) in the blood, or that provide a
built-in control on the PT measurement, or that measure another
blood parameter (such as APPT)
[0076] FIG. 8 is a schematic illustration of an embodiment in which
multiple measurement areas are "in series", meaning that they fill
sequentially. In this embodiment, measurement areas 118S, 218S, and
318S fill sequentially, through a single channel 116S, until the
sample reaches stop junction 122S. A potential drawback of this
design is that sample passing from one measurement area to the next
may carry over reagent.
[0077] FIG. 9 is a schematic of another embodiment of a device that
is adapted for multiple sequential tests. In that embodiment stop
junctions 122T, 222T, and 322T permit a user to control the timing
of sequential filling of measurement areas 118T, 218T, and 318T. In
operation, bladders 114, 214, and 314 are all compressed before a
blood sample is applied to sample well 112. Bladder 114 is then
released to draw blood into measurement area 118T to stop junction
122T. At a selected later time, bladder 214 is released to permit
blood to break through stop junction 122T and enter measurement
area 218T to stop junction 222T. Finally, when the user wishes to
use measurement area 318T, bladder 314 is decompressed, permitting
sample to break through stop function 222T and flow to stop
junction 322T. The device of FIG. 9 must be carefully formed, since
the force drawing sample into the device--caused by decompressing a
bladder--must be balanced against the opposing force--exerted by a
stop junction. If the drawing force is too great, a stop junction
may prematurely permit sample to pass; if it's too small, it will
not draw the sample through a stop junction, when that is
intended.
[0078] FIG. 10 depicts a preferred embodiment of the present
device. It is a parallel multi-channel device that includes bypass
channel 152P. Bypass channel 152P serves a purpose in this device
that is analogous to that served by bypass channel 52 in the device
of FIG. 6, which was described above. Measurement area 118P
contains thromboplastin. Preferably, measurement areas 218P and
318P contain controls, more preferably, the controls described
below. Area 218P contains thromboplastin, bovine eluate, and
recombinant Factor VIIa. The composition is selected to normalize
the clotting time of a blood sample by counteracting the effect of
an anticoagulant, such as warfarin. Measurement area 318P contains
thromboplastin and bovine eluate alone, to partially overcome the
effect of an anticoagulent. Thus, 3 measurements are made on the
strip. PT time of the sample, the measurement of primary interest,
is measured on area 118P. However, that measurement is validated
only when measurements on areas 218P and 318P yield results within
a predetermined range. If either or both of these control
measurements are outside the range, then a retest is indicated.
Extended stop junction 422 stops flow in all three measurement
areas.
[0079] FIG. 11 depicts a device that includes bypass channels 152S
and 252S to permit timed filling of measurement areas 118T and
218T. Operation of the device of FIG. 11 is analogous to that of
the device of FIG. 9, described above, with the following
exception. First bypass channel 152S has a region in which a
reagent that causes clotting, such as thromboplastin, is coated. As
a first measurement is made in reagent area 118T, a clot forms in
blood that had been drawn into bypass channel 152S. Thus, when the
second bladder is decompressed, blood is blocked from being drawn
through bypass 152S and instead is drawn though stop junction 122T
to measurement area 218T and bypass channel 252S.
[0080] All the previous figures depict the device of this invention
as a laminated strip structure; however, the device could also be
an injection-molded structure of the type shown in FIGS. 12 and 13.
FIG. 12 is an exploded view of an injection-molded device 110,
including top layer 126 and bottom layer 128 sandwiching
intermediate layer 124. The intermediate layer has depressions in
its top surface that form sample port 112, channel 116, measurement
area 118, and optional bypass channel 152. Stop junction 122 passes
through the thickness of intermediate layer 124. Sample flow stops
at the interface between stop junction 122 and channel A, which is
formed by a depression in the bottom surface. Thus, the sample
flows from sample port 112 through channel 116 to measurement area
118 into stop junction 122.
[0081] The principle of operation of the injection molded device is
the same as described above. It provides greater flexibility in the
design of the stop junction, as well as the other elements of the
device, because a wide range of channel cross sections are
feasible. The molded structure also provides more rigidity,
although it is substantially more costly.
[0082] The following examples demonstrate the present invention in
its various embodiments, but are not intended to be in any way
limiting.
EXAMPLE 1
[0083] A strip of this invention is made by first passing a
double-sided adhesive tape (RX 675SLT, available from Scapa Tapes,
Windsor, Conn.) sandwiched between two release liners into a
laminating and rotary die-cutting converting system. The pattern
shown in FIG. 6, with the exception of the stop junction, is cut
through the top release liner and tape, but not through the bottom
release liner, which is then removed as waste, along with the
cutouts from the tape. Polyester film treated to be hydrophilic
(3M9962, available from 3M, St. Paul, Minn.) is laminated to the
exposed bottom side of the tape. Reagent (thromboplastin, available
from Ortho Clinical Diagnostics, Raritan, N.J.) is then printed
onto the reagent area (18) of the polyester film by bubble jet
printing, using printing heads 51612A, from Hewlett Packard,
Corvallis, Oreg. A sample port is cut in untreated polyester film
(AR1235, available from Adhesives Research, Glen Rock, Pa.) and
then laminated, in register, to the top of the double-sided tape
(after removing the release layer). A die then cuts the stop
junction through the three layers of the sandwich. Finally, strips
of single-sided adhesive tape (MSX4841, available from 3M, St.
Paul, Minn.) are applied to the outside of the polyester layers to
seal the stop junction.
EXAMPLE 2
[0084] A procedure that is similar to the one described in Example
1 is followed to make a strip of the type depicted in FIG. 10.
Reagent that is bubble-jet printed onto areas 118P, 218P, and 318P
is, respectively, thromboplastin; thromboplastin, bovine eluate,
and recombinant Factor VIIa; and thromboplastin and bovine eluate
alone. The bovine eluate (plasma barium citrate bovine eluate) is
available from Haemotologic Technologies, Burlington, Vt.; and
recombinant Factor VIIa from American Diagnostica, Greenwich,
Conn.
[0085] Measurements made on a whole blood sample using the strip of
this Example yield a curve of the type shown in FIG. 5 for each of
the measurement areas. The data from the curves for the controls
(measurement areas 218P and 318P) are used to qualify the data from
the curve for measurement area 118P. As a result, the PT time can
be determined more reliably than can be done with a strip having a
single measurement area.
EXAMPLE 3
[0086] The device of FIGS. 12 and 13 is formed by sandwiching
middle layer 124 between top layer 126 and bottom layer 128. The
middle and bottom layers are injection molded polycarbonate
(Lexan*121) and have thicknesses of 6.3 mm and 1.5 mm,
respectively. Top layer 126 is made by die cutting 0.18 mm Lexan*
8010 sheet. The elements are ultrasonically welded after the
reagent of Example 1 is applied to reagent area 118. The Lexan*
material is available from General Electric, Pittsfield, Mass.
[0087] The invention having been fully described, it will be
apparent to one of ordinary skill in the art that many
modifications and changes may be made to it without departing from
the spirit and scope of the present invention.
* * * * *