The U.S. Food and Drug Administration has licensed the first nucleic acid test, or NAT, systems intended to screen plasma donors. NAT systems are expected to help ensure the safety of plasma-derived products by permitting earlier detection of human immunodeficiency virus, or HIV, and hepatitis C virus, or HCV, in donors.
Although effective procedures for virus inactivation are required in the manufacturing of all U.S.-licensed plasma derivatives, removal of potentially infectious donations through donor screening limits the amount of virus contamination that the manufacturing process must clear.
NAT is a newly developed technology that allows very small amounts of genetic material, such as DNA and RNA, to be detected by a process of massive copying of a gene fragment. The systems permits highly sensitive detection of RNA from HIV type 1 (the HIV variant that is responsible for the vast majority of acquired immunodeficiency cases in the United States) and HCV in test pools of 512 plasma samples obtained from multiple donors. The use of pooled samples makes use of the NAT system cost-effective.
If the test pool is positive for either HIV or HCV, the individual donation suspected of containing a virus can be identified and excluded from manufacturing use. Also, the donor can be notified and deferred.
Currently, blood and plasma donors are tested for antibodies to HCV and HIV, as well as HIV-1 antigens, which are the virus’s own proteins. There is a "window period," however, during which a donor can be infected, but still test negative during screening.
With the use of NAT systems, the "window period" for detection of HCV is reduced from 82 days to 25 days. For HIV-1, the average window period with antibody tests is 22 days. The use of antigen testing shrinks the window period to 16 days, and testing using the NAT systems reduces it to 12 days.
According to a press release from the FDA, in clinical trials, the NAT systems detected a number of HIV and HCV infections that would have been missed by previously licensed test methods, thus confirming the effectiveness of these systems.
