New Methode of Blood Screening

Nucleic Acid Testing: Investigations to Detect Blood Viruses More Effectively Fact Sheet

Investigations to Detect Blood Viruses More Effectively: Nucleic Acid Testing The American Red Cross continues to be committed to finding new technologies that make the blood supply safer. Nucleic Acid Testing has been used as an investigational technique to detect viruses earlier after infection in donated blood than existing tests.

The American Red Cross has been studying NAT under an Investigational New Drug (IND) application submitted to the Food and Drug Administration (FDA) for evaluating new technologies.

What Is the Challenge?
The screening process to detect viruses, such as HIV-1 and hepatitis C virus (HCV) in donated blood works primarily by identifying the antibodies formed when the body begins to fight them. FDA licensed tests for HIV-1 include tests designed to detect both the antibody and the antigen. While current screens are extremely sensitive, the Red Cross and most of the other collectors of whole blood and source plasma in the U.S. have been investigating a new technology.

Researchers are evaluating whether this new technology can improve safety by identifying viruses even before the body begins to produce antibodies (the body's response to a virus). How Is the Red Cross Meeting the Challenge? Nucleic acid testing involves a new technology that is being investigated under an Investigational New Drug application submitted to the FDA.

The testing is being performed to determine if it can detect the genetic material of a transfusion-transmitted virus like HIV-1 without waiting for the body to form antibodies- potentially offering an important time advantage over current techniques. On March 3, 1999, the Red Cross began NAT for nine of its Blood Services regions.

By June 1999, the Red Cross used NAT in all Blood Services regions. Today, approximately 25,000 samples a day are tested from all 36 Red Cross Blood Services regions and some non-Red Cross facilities at Red Cross NAT laboratories in San Diego, Detroit, St. Louis, Charlotte and Philadelphia.

The Red Cross initially used NAT to screen donors for HCV and HIV-1. While the risk of those viruses in volunteer donors is very low, the Red Cross conducted the studies to see if NAT could further reduce the "window period" for donor blood.

The window period is the length of time after infection that it takes to detect antigens of the virus or for a person to develop enough specific antibodies to be detected by current testing. For HCV, studies indicate that the window period may be reduced by 40-60 days from the total window period with antibody testing of 70 days.

For HIV, studies suggest that the window period is reduced by 6 days (from a 22-day window period to a 16-day window period) with the use of the HIV-1 p24 antigen test; HIV-1 NAT has the potential to further reduce the window period by another 5 days.

A very small percentage of donors-about one per 4 million for HIV-1 and one per 275,000 for HCV-donate during the window period and test negative for these viruses on current screening tests but would be detected by the pooled NAT currently licensed. Data collected under the Investigational New Drug process indicate that approximately one to two additional donors per year who have HIV-1 and about 24 additional donors who have HCV will be detected by nucleic acid testing each year.

Without the investigational nucleic acid testing, these donors would not know of their condition until other testing was done or until they developed symptoms. The Red Cross has provided its investigational NAT data to the FDA for evaluation.

The FDA has used this data and similar data from other blood centers for licensure of HIV-1 and HCV NAT on February 28, 2002. All allogeneic donations from the Red Cross, those blood centers that are part of America's Blood Centers and the U.S. source plasma industry are using investigational NAT under a variety of different INDs.

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