Vacuum actuated blood collection assembly including tube of clot-accelerating plastic

An evacuated blood collection assembly includes a plastic container having a plasma-treated inside wall surface and an open end covered by a puncturable septum. The inside wall surface may also be abraded to increase surface area. The invention included a method to make the assembly.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates to blood collection and, more particularly, relates 
to a plastic blood sample collection assembly. 
2. Background 
Blood samples are routinely taken in evacuated tubes, such as glass 
VACUTAINER.TM. tubes (Becton, Dickinson and Company). One end of a 
double-ended needle is inserted into a patient's vein. The other end of 
the needle then punctures a septum covering the open end of the 
VACUTAINER.TM. tube so that the vacuum in the tube draws the blood sample 
through the needle into the tube. Using this technique, a plurality of 
samples can be taken using a single needle puncture of the skin. Plastic 
tubes have also been proposed for blood collection. Plastic offers a 
number of advantages over glass such as lower breakage, less weight in 
shipment, and easier disposal by incineration. 
Blood collected in evacuated tubes often must be clotted prior to clinical 
examination. It is desirable to form a dense clot as rapidly and 
completely as possible to facilitate clean separation of the clot from the 
serum layer by centrifugation. To achieve this end, both plastic and glass 
blood collection tubes frequently employ a clot activator. Typical 
activators are diatomaceous earth and particles of inorganic silicates, or 
biochemicals such as ellagic acid and thromboplastin. In one line of 
commercial blood collection tubes, for example, a coating of silicate 
particles in polyvinylpyrrolidone (PVP, a water soluble polymer) is 
affixed to the inside of the tube. When blood enters the tube, the PVP 
dissolves and silicate particles are released to initiate clotting. The 
PVP enters both the serum and clot. 
A problem with particulate activators is that finely divided particles may 
not pellet completely with the clot and may thus contaminate the serum 
layer and interfere with certain blood analyses. In addition, particles 
suspended in the serum may foul automatic blood analysis instruments. On 
the other hand, soluble biochemical activators can be disadvantageous 
because these cannot be easily separated from either the serum or blood 
clot and can interfere with both chemical and hematological assays. In 
particular, for highly specialized applications, such as blood banking, it 
is unacceptable to have either soluble activators or particulates in the 
cell mass of a blood clot because these cells are used in blood typing 
analyses. For this reason, samples for blood banking are routinely taken 
in glass tubes and rely on the clot activating property of the glass to 
induce clotting. There is a need in the art of blood collection for 
equipment which provides an enhanced rate of blood coagulation without 
leaving any soluble or particulate material in the serum layer or in the 
clot on centrifugation, thus avoiding potential interference with clinical 
tests, and particularly in blood banking procedures. The present invention 
is directed to fulfilling this need. 
SUMMARY OF THE INVENTION 
A blood collection assembly includes a tube having a bottom wall continuous 
with a side wall. The side wall defines an open end and the bottom wall 
defines a closed end. Together the bottom and side walls define an inside 
wall surface. The open end is covered by a puncturable septum, and the 
tube is evacuated. The inside wall surface is treated with a plasma from a 
process gas and may additionally be abraded to have greater surface area. 
A second aspect of the invention is a method to make the assembly of the 
invention. In one embodiment of the method, the inside wall of the tube is 
treated with a plasma to introduce a heteroatom to the surface of the 
wall. In a second method embodiment, the inside wall surface is abraded to 
be rough for greater surface area. In the preferred method, the inside 
wall of the tube is both abraded and plasma-treated. 
Thus the invention provides a plastic tube which retains the advantages of 
plastic and overcomes the disadvantage of poor and slow coagulation in 
plastic. The plasma treatment and abrasion modify the chemistry of the 
inside wall of the tube so that clotting is accelerated but no particulate 
or soluble clotting activators or binders are present to contaminate 
either the serum or the clot. The assembly of the invention is 
particularly well suited for blood bank operations.

DETAILED DESCRIPTION 
While this invention is satisfied by embodiments in many different forms, 
there will herein be described in detail preferred embodiments of the 
invention with the understanding that the present disclosure is to be 
considered as exemplary of the principles of the invention and is not 
intended to limit the invention to the embodiments illustrated and 
described. The scope of the invention will be measured by the appended 
claims and their equivalents. 
The blood collection assembly of the invention may include any container 
having a closed end and an open end. Suitable containers are, for example 
bottles, vials, flasks and the like, preferably tubes. The invention will 
henceforth be described in terms of the preferred tube. FIG. 1 illustrates 
the tube of the invention. A tube 10 has a bottom wall 12 defining a 
closed end 14 and a side wall 16 defining an open end 18. Bottom wall 12 
and side wall 14 are continuous and together define an inside wall surface 
20. An area 22 of inside wall surface 20 is rough as a result of being 
abraded. While FIG. 1 shows only a portion of the inside wall near the 
bottom of the tube to be rough, this is merely the preferred embodiment of 
the invention which maintains the upper portion of the tube fully 
transparent for clear visibility of the serum layer. It is of course 
evident that, if desired, the entire inside surface or any other portion 
thereof could be abraded. The open end 18 of tube 10 is covered with 
puncturable septum 24. Tube 10 covered by septum 24 is evacuated. 
Evacuated tubes for blood collection are standard in the art as, for 
example, VACUTAINER.TM. brand tubes (Becton, Dickinson and Company). 
The tube may be of plastic. Suitable plastics are polyethylene 
terephthalate (PET) and preferably polystyrene (PS). While the tube may be 
of any size, the invention is particularly well suited to evacuated blood 
collection tubes. 
These tubes are generally cylindrical, 50 to 150 mm in length and about 10 
to 20 mm in diameter. 
In accordance with the invention, it has been found that treatment of the 
tube with a plasma results in a surprising increase in the rate of 
clotting of a blood sample. The plasma may be generated from any suitable 
process gas. A representative but not limiting list of suitable process 
gases includes nitrogen, ammonia, carbon dioxide, sulfur dioxide, air and 
oxygen wherein air and oxygen are preferred. The tube may be placed open 
end up between the electrodes of a conventional plasma generator equipped 
with a pressure gauge, a gas inbleed and a vacuum connection. Suitable 
electrodes may be of any conducting material, although stainless steel and 
aluminum are preferred. The width and shape of the electrodes is not 
critical. Any suitable ionizing plasma may be used, as, for example, a 
plasma generated by a corona discharge or preferably a glow discharge. 
A wide range of power settings, radio frequencies and duration of exposure 
of the plastic surface to the plasma may be used. Ranges for these 
parameters which provide advantageous results are DC or AC power levels up 
to 200 watts, from about 0.1 to about 50 megahertz and from about 0.1 to 
30 minutes. Preferred ranges are 10-50 watts, 10-20 megahertz and 2-10 
minutes respectively. Any gas pressure may be used, however, gas pressures 
are advantageously maintained at 5 mm of Hg or below in order to benefit 
from reduced voltage requirements. Ambient temperature for plasma 
generation is preferred. 
The plasma treatment results in introduction of polar functional groups 
into the surface of the plastic. The functional group depends on the 
process gas used to generate the plasma. For example, after plasma 
treatment, the surface may contain oxygen, nitrogen or sulfur atoms. These 
groups cause the plasma-treated surface to have a clot activating property 
similar to and even somewhat greater than that of glass. The examples and 
the drawings show the accelerated clotting rates of the plasma-treated 
plastic surfaces relative to those of glass and untreated plastic. 
In the preferred embodiment of the invention, the inside wall surface of 
the tube is abraded to have a rough surface and thereby an increased 
surface area. The plasma treatment may be performed prior to or preferably 
subsequent to abrading. The surface may be roughened by any conventional 
chemical or mechanical method, or during the tube forming process. Most 
conveniently, the surface is merely rubbed with an abrasive, such as with 
sand or emery paper. No limitation is placed on the grit of the abrasive, 
although it has been found that a medium grit sandpaper gives the greatest 
increase in surface area. Most preferably, the portion of the inside wall 
surface at or near the bottom of the tube is roughened, and the remainder 
of the tube is not roughened, as this maintains the maximum clarity of the 
tube for observation of the serum layer after centrifugation. It is, of 
course, understood that the entire inside wall surface is preferably 
treated with the plasma. 
EXAMPLE I 
Clot activating properties of the plasma treated tubes of the invention 
were assessed by comparison of the time required to clot platelet poor 
plasma (PPP) or whole porcine (pig) blood to that in untreated PS and 
glass tubes. PPP was prepared by separating cells by centrifugation of 
citrated porcine blood (Environmental Diagnostics Inc.). Approximately 3 
ml of PPP or whole blood were added to the tubes and temperature was 
equilibrated to room temperature in a water bath for 15 minutes. Following 
equilibration, 200 .mu.l of 0.2 M CaCl.sub.2 per ml or PPP or blood was 
added to initiate coagulation. Tube contents were mixed on a laboratory 
inverting mixer and time of clotting noted for each tube type. Clotted PPP 
or whole blood was distinguished from nonclotted by an obvious change from 
a fluid state to a gelatinous state which did not flow in the tube on 
rotation. Clotting time was measured at this point. 
EXAMPLE II 
Plasma Treatment 
A. A PS tube (Becton Dickinson, FALCON.TM., 13 mm.times.75 mm) was exposed 
to an oxygen plasma generated in a conventional planar diode plasma unit 
operated at about 50 watts of an RF frequency of 13.56 megahertz at a 
pressure of 200-300 mTorr for about 5 minutes to produce a highly oxidized 
surface chemistry. 
B. In the same way as in A, a tube of impact modified PS (K resin, 
Phillips), a polypropylene (PP) tube (ESCORENE.TM., Exxon) and PET tubes 
(Eastman grades 2182 and 1042) were plasma treated. Clot activation 
properties of the tubes of the invention and control tubes are set forth 
in FIG. 2 in which the tube types are as follows: 
Using whole blood: 
1. PS FALCON.TM. 
2. PS FALCON.TM. plasma treated 
Using PPP: 
3. glass 
4. glass plasma treated 
5. PS FALCON.TM. 
6. PS FALCON.TM. plasma treated 
7. PS K resin 
8. PS K resin plasma treated 
9. PP 
10. PP plasma treated 
11. PET 2182 
12. PET 2182 plasma treated 
13. PET 1042 
14. PET 1042 plasma treated 
It is seen from FIG. 2 that plasma treatment of PS tubes lowers the clot 
time of whole blood by more than 8 fold (tube types 1 and 2). Clot time of 
PPP in plasma treated PS is reduced by about 2.5 fold compared to 
non-plasma treated PS (tubes 5-8). Clot time of PPP is also reduced about 
2-2.5 fold in PET tubes (tubes 11-14) on plasma treatment, but plasma 
treatment of PP had substantially no effect on PPP clotting (tubes 9 and 
10). 
EXAMPLE III 
The lower half of PS tubes (FALCON.TM.) were mechanically abraded using 
medium-grit sandpaper to give a rough interior wall surface. FIG. 3 
compares clot time observed in these tubes before and after plasma 
oxidation performed as described in Example II. In FIG. 3, the tube types 
are as follows: 
1. PS FALCON.TM. 
2. PS FALCON.TM. plasma treated 
3. PS FALCON.TM. abraded 
4. PS FALCON.TM. abraded and plasma treated 
It is seen that abrading to give a rough surface of higher surface area 
reduces clot time to PPP by about 30% (tube 3 compared to control tube 1 
), and that plasma treatment of the roughened surface (tube 4) reduces 
clot time by a factor of 5 compared to control tube 1.