Note: Descriptions are shown in the official language in which they were submitted.
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BACKGROUND OF THE INV~NTION
This invention relates to a device which filters, isolates,
and contains for sampling or storage, the supernatant fluid from
a mixture of immiscible liquids or a slurry which has been
stratified by centrifuging or standing. More specifically, it
relates to a new and improved means for processing blood serum
specimens which are to be used in automatic clinical chemistry
analyzers.
In order to understand the conditions and problems inherent
in clinical laboratory practice, the following discussions are
pertinent.
1. Clinical laboratories employing automatic analyzers
frequently process hundreds of blood specimens per day. Each
individual specimen can require a wide variety of determinations.
Often, more than one type of analyzer is needed to achieve the
desired analyses. Obviously, maintaining the identity of large
numbers of specimens and correlating multiple test results with
the proper parent specimen is a problem of great complexity and
importance. Errors in sample identification may conceivably
contribute to the death of a patient.
2. The automatic sampling modules of existing clinical
analyzers are limited in several ways by mechanical considerations.
For instance, the vessels containing serum to be aspirated by the
sampler must be of uniform dimensions, particularly height, so
that the sample probe can enter them and function property. This
situation is normally met by transferring serum specimens for
sampling to a series of uniform sample cups contained in a
suitable rack. A problem arises, however, from such a transfer
of serum to a sample cup in that the new cup requires labeling in
some form, and this creates a potential source of identification
errors.
3~ Any volume of each serum specimen remaining after
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analysis is routinely stored in the clinical laboratory for
several days so that check analyses can be made if necessary.
Under most circumstances, such remaining serum volumes are
decanted into special individual containers for refrigerated
storage. The problem again arises that this additional transfer
can require a further labeling operation and create another
source of potential identification errors.
4. Still another problem arises in that each transfer
of serum from one vessel to another creates a potential for
chemical contamination of the specimen. Moreover, each transfer
by decanting or pipetting creates a potential for contaminating
the technical personnel with diseased serum.
5. Automated clinical chemistry analyzers themselves are
often a problem because they are especially susceptible to
clogging by small particles. Even serum which has been centrifuged
still requires filtering.
6. It is well known that blood serum should be completely
isolated from blood cells as soon as possible because ionic and
osmotic exchanges take place, across cell walls, between serum
and cells. Incomplete or delayed isolation of these blood
components raise a potential problem of inaccurate analytical
results.
SUMMARY OF THE INVENTION
The present invention provides a device which filters,
isolates and serves as a subsequent sample container for the
supernatant fluid from a mixture of immiscible liquids or a slurry
which has been stratified. The device is particularly useful as
` a means for processing blood serum specimens which are to be used
in automatic clinical chemistry analyzers. In general, it
comprises an outer (parent) blood tube, an inner telescoping
plunger tube, a piston head having a downwardly extending inlet
tube upon which is mounted a slidingly removable piston seal, and
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a tension loaded diaphragm valve on the upper end of said
depending inlet tube.
An important feature of my invention is that the plunger
assembly can be telescoped down into the packed cell mass in
the parent blood tube -- after the serum has been isolated and
filtered -- without first removing said plunger tube or
decanting the serum, a feature which has several important
advantages:
(a) Telescoping the plunger tube into the blood tube
results in an assembly of uniform height where the top of the
plunger tube is almost flush with the top of the parent blood
tube. This minimal and uniform height of the assembly allows
an automatic sampler to aspirate serum directly from the plunger
tube positioned in its parent blood tube.
(b) Decanting serum from the device is unnecessary, thus
minimizing labor and possible contamination of the sample.
(c) Sampling from the plunger tube disposed in its parent
; blood tube bearing the original identifying label avoids the
labor of labeling an auxiliary vessel and minimizes indentification
errors.
(d) Sampling from the plunger tube eliminates the cost of
one or more auxiliary vessels.
(e) Serum may be safely stored for reference in the
- telescoped assembly from which samples have been removed, thus
; avoiding the use of auxiliary sample vessels. This minimizes
labor, possible contamination and possible identification errors.
It also eliminates the cost of auxiliary storage vessels.
(f) Since decanting of serum or removal of the device
from its parent tube is not required, possible contamination of
personnel is minimized.
A second feature of the new device is that collected and
filtered serum is isolated from packed blood cells by means of a
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mechanical barrier, thus preventing ionic or osmotic interchange
even during long time storage.
A third feature of the new device is that, during use,
the rubber piston ring is separated from the surface of the
serum being collected by a column of trapped air. This feature
precludes the wiping of cellular or other debris from the inner
wall of the parent blood tube into the serum being collected.
Contamination from this source could be of importance in certain
analyses (e.g. ensymes).
A fourth feature of the device is that it may be used to
advantage even in laboratories where analyses are performed
manually.
This invention thus provides a means for processing blood
serum for clinical chemistry analysis which: filters the serum;
isolates serum from cells; provides an integral sample and storage
vessel which is compatible with use in automatic sampling machines;
minimizes potential sample contamination; minimizes sample
identification errors; minimizes labor and equipment costs.
BRIEF DESCRIPTION OF THE DRAWINGS
Fig. 1 is a side-elevational view of an assembled tubular
apparatus with parts broken away to show in section the interior
arrangement of parts at the beginning of a filtration operation;
Fig. 2 is a similar view showing the parts after the
separated serum has passed through the filter and valve into the
plunger tube and after the plunger tube has been retracted about
one-fourth inch;
Fig. 3 is another view showing the relation of the parts
after the filtration has been completed and the piston sealing ~ -
ring has been displaced and after the plunger tube has been
telescoped completely down into the parent blood sample tube;
Eig. 4 is a disassembledview of the parts of the piston
before assembly as a piston in the lower end of the plunger tube,
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shown in section;
Fig. 5 is an assembly of the piston parts in the lower
end of the plunger tube, shown partly in section; and
Fig. 6 is a fragmentary side elevation view of an
optional enlargement of the upper end of the plunger tube; and
Fig. 7 shows a side elevational view partly in section of an
optional form of the rigid plastic piston body, whose upper
surface is conical. -
DESCRIPTION OF THE PREFERRED EMBODIMENT
Referring to the drawings, the outer or blood tube 11 is
a cylindrical tube of the kind in which blood samples are commonly
delivered to the laboratory. An inner plastic plunger tube 12 is
movably telescoped within the blood tube 11, its lower end being
fitted with a piston head 13 which consists of a rigid plastic
body 14 having an upwardly facing cup-shaped portion 15 with a
depending skirt 16, whose outer surface closely fits inside the
lower end of said plunger tube 12. The depending skirt 16 of the
cylindrical body may also be provided with an out-turned rim 16A
upon which the lower end 17 of the plunger tube 12 is positioned.
The body 14 of the piston head has an integral depending tubular
member 18 of smaller diameter than the cupped portion 15, the
tubular member 18 communicating with the inside of the cup portion
15 through an apertured valve seat 19 which projects upwardly to,
or slightly above, the height of the rim 20 of the upper portion
15. A flexible sealing ring 21 of rubber or other soft polymer,
having a thinner outer portion 22 which makes sliding sealing
contact with the inside wall 23 of the hlood tube 11, and has a
central opening 24 which makes sliding frictional contact on the
outer surface of the depending tubular member 18.
An elastic membrane 25 is attached on or over the rim 20
of the upper portion 15 of the body 14, the membrane contacting
at its center the upper surface of the valve seat 19. The
membrane 25 is preferably a rubber dam of approximately 0.015
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inches thickness, and is provided with one or more small openings
29 positioned away from the valve seat, for discharge of filtered
serum into the upper part of the plunger tube 12.
The membrane is preferably attached over the upper portion
15 of the body 14 by stretching it during assembly between the
lower end of the plunger tube 12 and the upper portion 15 of the
body 14. The tension thus obtained is important in the valve
function because it assures positive seating action of the
membrane on the valve seat 19. The tension on the membrane can be
varied in a predictable manner by altering certain design
parameters of the rigid body 14. In this manner, it is possible
to produce valves which will open only when pressure differentials
exceeding pre-selected values are applied. A groove 27 may be
provided in the outer cylindrical surface of the body 14 to
receive the edge of the membrane 25.
The filter means 28 consists of fibrous or porous materials
such as synthetic fibers, glass fibers, porous polymers, or the
like, shaped into pads or plugs to frictionally fit in the
tubular opening 18A. The filter material must not interfere with
the chemistry of the serum passing through it. Fibrous cellulose
acetate or sintered polyethylene are suitable if the effective
pore size of the filter is in the range of 10 to 100 microns. The
filter means 28 is frictionally fitted within the depending tubular
member 18.
Optionally, the upwardly facing portion 15 of the body 14
is a conical surface except for the valve seat 19 with its orifice
30, as shown in Fig~ 7.
The operation of the serum processing device will be
understood by referring to Figs. 1, 2 and 3. In Fig. 1, the
plunger tube 12 is shown as just entering the blood sample tube 11
in which the blood cells have been settled out of the serum by the
familiar operation of centrifuging. The sealing ring 21,
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frictionally attached to the depending tubular member 18 of
the piston head 13, makes sealing contact with the inside wall
of the blood sample tube 11 above the level of the contained
serum, and the lower end of the depending tube 18 makes contact
with the surface of the serum. An air pocket is maintained
between the sealing ring 21 and the top surface of the serum.
Said air pocket prevents any intact blood cell, debris, or
chemically active residue wiped from the inner wall of blood
tube 11 be sealing ring 21 from contacting and contaminating
the serum being filtered and collected as the piston is forced
downward. The filtered serum passes through the opening 30 in
valve seat 19 and exits through the small openings 29 in the
membrane 25, into the plunger tube 12 above the piston head 13.
In use, as the lower end of the depending tubular member
18 reaches the mass of packed cells in the blood tube 11, the
downward movement is halted. At this point in the operation,
the user may follow either of two alternative procedures depending
upon his need.
If the user intends to analyze the serum by manual methods,
or if he chooses to decant aliquots of filtered serum for
immediate use and store the remaining serum for future decanting,
he would proceed as follows. The plunger tube 12 would be
withdrawn one-eighth to one-fourth inches. Such upward motion
would cause depending tubular member 18 to move slidingly upward
in the central opening 24 of sealing ring 21. Said sealing ring
would remain stationary because of friction on the walls of the
blood tube and because of vacuum. This configuration of parts
is shown in Fig. 2. It will be noted that both depending tubular
member 18 and plunger tube 12, containing filtered serum, are
completely isolated from the blood cells. It will be further
noted that the air space above the cells remains sealed by sealing
ring 21, and decanting of filtered serum may be accomplished
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without interference from cells. Storage of filtered serum in
the parent blood tube carrying its original identification is
convenient in this configuration.
Alternatively, should the user desire to process the
filtered serum in an automatic analyzer, he would proceed as
follows. Plunger tube 12 would be withdrawn three-eights inch
or more which would cause depending member 18 to slide completely
out of central opening 24 of sealing ring 21. Sealing ring 21
would remain lodged in its horizontal position in blood tube 11.
Now, the plunger tube 12 would again be moved downward into blood
tube 11 and the depending member 18 would dislodge the sealing
ring 21 and force it down into the blood cell mass. The plunger
tube 12 would be further pushed down until its top enlargement
is seated in the top portion of the blood tube 11. This
configuration is shown in Fig. 3, the serum being isolated from
cells by valve membrane 25. Tension placed upon membrane 25
during assembly of the device prevents upward flow of the cell-
containing fluid even when the hydrostatic head of serum is
reduced to zero.
Referring again to Fig. 3, it should be noted that the
enlargement of the upper end, 12A, of plunger tube 12 serves
several purposes. First, the enlargement forces positive alignment
of the axes of plunger tube 12 and blood tube 11. Such alignment
` is necessary for the use of automatic sample probes. Second, the
enlargement acts as a filler between the inner wall of blood tube
11 and the outer wall of plunger tube 12. Third, the enlargement
serves to lock the plunger tube 12 to the blood tube 11 when
these parts are fully telescoped. This feature minimizes the
possibility of spilling red cel~s if the assembly is accidentally
overturned during storage (plunger tube 11 would normally be
stoppered for storage).
The configuration shown in Fig. 3 permits a suitable
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automatic sampling machine such as those used with clinical
chemistry analyzers, to withdraw aliquots from a rack of tubes
havil~g uniform and minimal heights.
The advantages of my invention will be clear from the
above description of the parts and their functioning in use.
