Date: Fri, 14 Jun 1996 01:48:18 -0400 From: "Flynn Mclean" Subject: CDC National AIDS Hotline Training Bulletin #173 ................................................................. CENTERS FOR DISEASE CONTROL AND PREVENTION HIV/AIDS PREVENTION CDC NATIONAL AIDS HOTLINE TRAINING BULLETIN ................................................................. March 20, 1996 #173 These are answers from Centers for Disease Control and Prevention (CDC) to questions concerning testing and counseling blood and plasma donors for HIV type 1 antigen: Guidelines of the U.S. Public Health Service, as published in the March 4, 1996, MMWR Reports and Recommendations. 1. What is this MMWR report about? It is about a way to further improve the safety of blood and plasma transfusions by adding an additional screening test to the extensive set of interview and laboratory procedures already in place. Blood and plasma donations in the United States have been tested for antibody to HIV-1 since March 1985 and HIV-2 since June 1992. Since most people develop detectable antibodies to HIV within a few weeks after infection, these tests have virtually eliminated HIV transmission through contaminated blood transfusions. To maintain an even safer blood and plasma supply, the Food and Drug Administration (FDA) recommended in August 1995 that all donated blood and plasma also be tested for HIV-1 p24 antigen, which appears before antibody development. FDA has recently licensed the p24 antigen test for use among blood and plasma donors. In anticipation of the implementation of national screeniing, this Public Health Service report provides guidance for interpreting HIV-1 p24 antigen test results, counseling, and follow-up of blood and plasma donors. 2. What is the current risk of getting HIV infection from a blood donation? Because of the screening procedures already in place, CDC estimates that 1 in 450,000 to 1 in 660,000 donations are infectious for HIV but do not test positive by currently available HIV antibody tests. This is equal to about 18-27 donations of HIV-infected blood per year out of about 12 million units donated nationally. 3. What are HIV antigen and antibody? Antigens are proteins such as those found in bacteria and viruses. The p24 antigen is the protein found at the core of the virus. Antibodies are proteins made by the body's immune system in response to infection. The presence of antigen stimulates the immune system to begin to make specific antibodies. Depending on the infected person's immune response, HIV antigen is detectable in a few days or weeks after infection with HIV. On average, p24 antigen is detected an estimated 6 days before HIV antibody becomes detectable through testing. When antibodies to HIV become detectable, the antigen is usually no longer detectable because the antibody reacts chemically with all the antigen and forms antibody-antigen complexes that are not detectable on laboratory tests. 4. What is the infectious "window period" for HIV? The infectious "window period" is the time period between when a person recently infected with HIV becomes capable of transmitting HIV to others and the time when the infection becomes detectable by laboratory testing. With the first HIV-antibody tests used from 1985 through 1990, the average length of time before detectable antibody development (window period) was 45 days. The average window period with newer, protein-based HIV antibody tests is 25 days; the addition of the p24 antigen test will subtract an average of 6 days from this window period. 5. Has CDC changed its recommendations about when an individual should seek HIV antibody testing? No. Recommendations for voluntary HIV counseling and antibody testing at test sites have not been changed. (CDC. "HIV Counseling, testing and referral: standards and guidelines, May 1994.) Guidelines for counseling and testing individual patients already take into account the window period and recommend follow-up antibody testing. Antigen testing detects HIV infection only a few days before antibody testing does. And the time in which the antigen can be found is very short--once antibodies are detectable, antigen is often not detectable. Antibody testing at the recommended intervals is the best way for health care providers to routinely diagnose HIV in adults and children 18 months or older. 6. What is an HIV p24 antigen test? The p24 antigen screening test is an enzyme immunoassay. The test yields a positive reaction only during the week or so before the HIV-1 antibody test becomes reactive. It yields a negative result before and after that short period of positive reactivity. 7. How are results interpreted? If the test is nonreactive (negative), the test result is reported as negative. If the test is reactive (positive), the p24 antigen test is repeated twice on the same blood sample. If the two repeated tests are nonreactive, the test result is reported as negative. If one or both of the repeated tests is reactive, the test is considered repeatedly reactive. A more specific, supplemental test called the neutralization assay is used to verify the presence of HIV-1 antigen. The neutralization assay should be performed on the blood sample before a donor is informed of any test results. 8. When will the p24 antigen testing of the blood supply begin? The HIV-1 p24 antigen test is now licensed by the FDA. Testing of the blood supply with the HIV p24 antigen test has begun in most areas and must begin in all parts of the United States within 3 months after the test was licensed by the FDA. 9. How much safer will the blood supply be with the addition of the HIV p24 antigen test? In August 1995, the FDA recommended screening the blood supply for p24 antigen as an additional safety measure. Among the 12 million annual blood donations in the United States, p24 antigen screening is expected to detect an average of 4 to 6 infectious donations per year (which would be divided into about 7-11 infectious components) that would otherwise not be removed by other screening. 10. What happens to the blood donation if the antigen test is positive? The donation is destroyed. 11. What should someone do if they get a positive p24 antigen test result with a positive supplemental (neutralization) test after donating blood? They should get confirmation of the results with repeat antigen or HIV antibody testing. They should be counseled that they are probably infected with HIV and informed of precautions to prevent transmission to others. Persons with a positive neutralization antigen test are permanently deferred from donating blood. On the other hand, most initially positive p24 antigen test results will likely be false-positive results and are probably not infected. Very few infections are expected to be found through antigen testing alone. This is why it is important to have results confirmed by follow-up antigen and antibody testing. 12. If donors are deferred from donating blood based on antigen test results, can they ever donate again? Some can. Donors whose samples are repeatedly reactive on the p24 antigen test, but have negative or invalid neutralization tests, are temporarily deferred from donating blood for at least 8 weeks. If after this time, their blood samples test negative for p24 antigen and HIV antibody, the donors are not infected and can donate blood. If after 8 weeks the antigen test is repeatedly reactive or the antibody test is positive, the donors are permanently deferred from donating blood--regardless of the neutralization test results. 13. Will the addition of antigen testing to the blood supply prompt people to donate blood to find out their HIV status? No one should donate blood to learn their HIV status. People at risk for HIV infection should not donate blood. Those who want to know their HIV status should seek counseling and testing at sites that use antibody testing to determine HIV infection. Disclaimer: CDC Hotline Training Bulletins The information in the "CDC Hotline Training Bulletins" is provided by CDC and NIH for use by the CDC National AIDS Hotline in responding to general questions from the public about HIV and AIDS. The bulletins are not intended to be comprehensive discussions of the subject areas. Treatment and drug therapy options change as new research and clinical experiences broaden scientific knowledge. Therefore, persons seeking information on drug therapy should refer to the product information sheet included in all drug packages for the most current and accurate information about a particular drug, especially if the drug is new or infrequently used. HIV-infected individuals should consult their personal physician for specific concerns about their health. For persons desiring more information on a specific topic, public, medical, and university libraries can provide excellent references. The AIDS Clinical Trials Information Service (800-874-2572) can provide information about ongoing HIV/AIDS clinical trials; the HIV/AIDS Treatment Information Service (800-448-0440) can assist with information about the latest treatments for persons with HIV infection or AIDS.