Efficient algorithm for pcr testing of blood samples

This application is a continuation of U.S. application Ser. No. 10/442,780 filed May 20, 2003, which application was a division of patent application Ser. No. 09/549,477, filed Apr. 14, 2000, now U.S. Pat. No. 6,566,052, which is a division of U.S. application Ser. No. 09/081,826 filed May 20, 1998, now U.S. Pat. No. 5,063,563, which is a division of U.S. application Ser. No. 08/778,610, filed Jan. 6, 1997, now U.S. Pat. No. 5,780,222, which is a continuation-in-part of U.S. application Ser. No. 08/683,784, filed Jul. 16, 1996, now U.S. Pat. No. 5,834,660 which is a division of application U.S. application Ser. No. 08/419,620, filed Apr. 10, 1995, now U.S. Pat. No. 5,591,573, the contents of which are expressly incorporated herein by reference.

The present invention relates generally to systems and processes for preparing and analyzing samples taken from plasma donations to uniquely identify donations which are virus contaminated. In particular, the invention relates to an apparatus and process for forming individual, separately sealed, and connected containers holding samples of the same plasma as is contained in the donation. The invention also relates to an apparatus and process for forming initial screening test pools from the containers and testing the pools for the presence of a virus in accordance with an algorithm to identify individual contaminated donations in the fewest number of testing cycles.

Blood, plasma, and biological fluid donation programs are essential first steps in the manufacture of pharmaceutical and blood products that improve the quality of life and that are used to save lives in a variety of traumatic situations. Such products are used for the treatment of immunologic disorders, for the treatment of hemophilia, and are also used in maintaining and restoring blood volume in surgical procedures and other treatment protocols. The therapeutic uses of blood, plasma, and biological fluids require that donations of these materials be as free as possible from viral contamination. Typically, a serology test sample from each individual blood, plasma, or other fluid donation is tested for various antibodies, which are elicited in response to specific viruses, such as hepatitis C (HCV) and two forms of the human immunodeficiency virus (HIV-1 and HIV-2). In addition, the serology test sample may be tested for antigens designated for specific viruses such as hepatitis B (HBV), as well as antibodies elicited in response to such viruses. If the sample is serology positive for the presence of either specific antibodies or antigens, the donation is excluded from further use.

Whereas an antigen test for certain viruses, such as hepatitis B, is thought to be closely correlated with infectivity, antibody tests are not. It has long been known that a blood plasma donor may, in fact, be infected with a virus while testing serology negative for antibodies related to that virus. For example, a window exists between the time that a donor may become infected with a virus and the appearance of antibodies, elicited in response to that virus, in the donor\'s system. The time period between the first occurrence of a virus in the blood and the presence of detectable antibodies elicited in response to that virus is known as the “window period.” In the case of HIV, the average window period is approximately 22 days, while for HCV, the average window period has been estimated at approximately 98 days. Therefore, tests directed to the detection of antibodies, may give a false indication for an infected donor if performed during the window period, i.e., the period between viral infection and the production of antibodies. Moreover, even though conventional testing for HBV includes tests for both antibodies and antigens, testing by more sensitive methods have confirmed the presence of the HBV virus in samples which were negative in the HBV antigen test.

One method of testing donations, which have passed available antibody and antigen tests, in order to further ensure their freedom from incipient viral contamination, involves testing the donations by a polymerase chain reaction (PCR) method. PCR is a highly sensitive method for detecting the presence of specific DNA or RNA sequences related to a virus of interest in a biological material by amplifying the viral genome. Because the PCR test is directed to detecting the presence of an essential component of the virus itself, its presence in a donor may be found almost immediately after infection. There is, theoretically therefore, no window period during which a test may give a false indication of freedom of infectivity. A suitable description of the methodology and practical application of PCR testing is contained in U.S. Pat. No. 5,176,995, the disclosure of which is expressly incorporated herein by reference.

PCR testing is, however, very expensive and since the general donor population includes a relatively small number of PCR positive donors, individual testing of each donation is not cost effective or economically feasible. Hence, an efficient and cost-effective method of testing large numbers of blood or plasma donations to eliminate units having a viral contamination above a pre-determined level is required.

One method of testing a large number of plasma donations is to pool a number of individual plasma donations. The pool is then PCR tested and the individual donations comprising the pool are either retained or disposed of, depending on the outcome of the PCR test. While reducing the number of PCR tests, and the costs associated therewith, this method results in a substantial waste of a significant portion of virus free donations. Since only a single donation with a viral contamination above a pre-determined level will cause a pool to test PCR positive, the remaining donations that contribute to a pool may well be individually PCR negative. This result is highly probable given that a relatively small number of PCR positive donors exist in the general donor population. In the conventional pooling approach, all donations comprising the pool are disposed of upon a PCR positive result, including those donations that are individually PCR negative.

In addition, plasma donations are often frozen soon after they are received. When samples of individual plasma donations are needed for pooling, each donation must be thawed, an aliquot of the blood or plasma removed from the donation, and the donation must then be refrozen for preservation. Multiple freeze-thaw cycles may adversely affect the recovery of the RNA or DNA of interest as well as the proteins contained within the plasma, thus adversely affecting the integrity of the PCR test. Moreover, each time an aliquot of individual plasma donations is withdrawn to form a pool, the donation is subject to contamination, both from the surrounding environment, and from the apparatus used to withdraw the aliquot. Further, if the donation contains a virus, it can contaminate other donations. In order to avoid introducing viral contaminants into an otherwise viral free donation, the sample taking apparatus must be either sterilized after each individual use, or used for taking only a single aliquot from a single individual donation and a new sample taking apparatus used for taking an aliquot from a subsequent individual donation. Either of these methods involves considerable expense and is quite time consuming.

Accordingly, there is a need for a process and system for obtaining multiple blood or plasma samples from individual donations such that particular samples may be pooled without contaminating the remaining samples. It is also desirable that the process and system is able to form such pools in a fast and efficient manner, without contaminating either a clinical testing lab technician or the testing laboratory environment.

In addition, it is desirable that the process and system provide for efficient and cost-effective testing of the blood or plasma donations to identify only uniquely PCR positive donations in the fewest possible number of testing cycles.

There is, therefore, provided in the practice of this invention a cost-effective and efficient process for preparing and testing samples from a multiplicity of blood or plasma donations to uniquely identify donations which are infected with virus as well as systems and devices for practicing the process.

The process of the present invention results in blood and plasma products being substantially safer because one can readily test for virus contamination in the blood or plasma supply directly. Cost-effective, high-sensitivity testing can be performed immediately, and contaminated donations identified, without regard to an infectivity window period.

In one embodiment of practice of the present invention, the process comprises the steps of providing a blood or plasma donation in a collection container. A flexible collection segment is connected to the container and is open to the inside of the container. The collection segment is filled with blood or plasma from the collection container, and a portion of the collection segment is sealed at both ends. The sealed portion of the collection segment is removed from the container and, either before or after the sealed collection segment portion is removed, a plurality of spaced-apart seals are provided at intervals along the length of the collection segment between the sealed ends. The segment portions in the intervals between adjacent seals define containers, wherein each such container contains a plasma or blood sample, and wherein the intervals between the seals provide a sufficient volume in each such container for the planned testing.

In a more detailed embodiment of the present invention, individual plasma donations are collected in a plasma collection bottle which has a testing container connected thereto by a flexible hollow tubing segment. After being filled with a donor\'s plasma the plasma bottle is tipped so as to transfer plasma to the testing container and the flexible tubing segment, thereby filling the tubing segment. The tubing segment is sealed at spaced-apart intervals along its length, the tubing segment portions in the intervals between the seals define pouches each of which contains a sample of the plasma donation. The tubing segment, which has been converted into a series of pouches, is then disconnected from the plasma collection bottle and frozen until needed for testing.

In an additional aspect of the present invention, the hollow tubing segment comprises a series of linked-together Y-sites, including an injection site provided on one leg of the Y, and where each branch leg of a particular Y-site which does not include an injection site is connected to the base of the next Y-site in the chain by a flexible plastic tubing segment. Spaced-apart heat seals are formed along the length of each flexible plastic tubing segment separating the Y-sites.

In a further aspect of the present invention a device for providing multiple heat seals along the length of the tubing segment filled with the blood or plasma donation comprises first and second opposed seal platens. Each seal platen includes a plurality of spaced-apart raised portions along its length alternating with recessed portions. The raised and recessed portions on the first platen are in registry with corresponding raised and recessed portions on the second platen. The opposed seal platens are moved together onto a plastic tubing segment filled with the blood or plasma donation to form heat seals on those portions of the tubing segment compressed between the raised portions and to form chambers defined by opposed recessed portions. The heat seals define a plurality of individual and sequential pouches therebetween and each chamber, defined by each closed pair of recessed portions, is configured to house a pouch.

In particular, a device for providing multiple heat seals along the length of the tubing segment filled with a blood or plasma donation is configured to be mounted on a commercially available heat seal apparatus, as an after-market modification.