Oct 28, 1996
HI! MR. SOWADSKY: I HAD READ IN YOUR PAGES THAT HIV IS ABOUT 99% POSITIVE IN 6 MONTH AFTER THE LAST RISKY SEX, BUT; WHAT IF YOU DONATE BLOOD BEFORE THIS 6 MONTH?; CAN BE A FALSE-NEGATIVE AND THIS BLOOD COULD INFECT OTHER PERSONS? LUIS, (ECUADOR) THANKS!
Response from Mr. Sowadsky
Luis, thank you for your question.
ince I live in the United States, I can only tell you how the American Blood Supply is tested and screened to avoid infection with the HIV viruses (types 1 and 2). I cannot tell you if these screening proceedures are done in all countries, including your own (Ecuador).
You are correct that it can take an HIV antibody test up to 6 months to show positive on these tests. This is why the American blood system goes beyond HIV antibody tests to screen the blood supply. The American blood supply is tested for both HIV-1 and HIV-2. It is also tested for Hepatitis B, Hepatitis C, HTLV-I and II, and syphilis.
If a person has been infected with HIV for less than 6 months, there is a possibility that a person can be infected, and it not be found by antibody tests. Therefore, in addition to antibody tests, the following proceedures are done in the American blood supply to make the blood supply even safer against the HIV viruses.
1) In addition to antibody tests, the American blood supply is tested with the p-24 antigen test. This test will usually show positive an average of 6 days before the antibody test will. Using this test (in addition to the antibody tests) will therefore shorten the window period by about a week. Once the antibody tests turn positive, the antigen test will once again revert back to negative. The p-24 antigen test cannot be used by itself to diagnose HIV infection. Other tests should be used in addition to p-24 antigen tests in the diagnosis of HIV infection. It is expected that by using the p-24 antigen test (in addition to antibody tests), that there will be approximately 10 fewer HIV infections in the American blood supply per year.
2) In addition to p-24 testing and antibody testing, before a person can donate blood in the USA, they must first be interviewed regarding their risks for HIV and other bloodborne diseases. They are asked questions about where in the world they have traveled, their drug use history, their sexual behaviors, and other risk factors that could put them at risk for HIV and other bloodborne diseases. If they are found to be at risk for HIV and other bloodborne diseases, they will not be permitted to donate blood.
We already know that manditory HIV antibody tests have significantly reduced the risks of HIV infection through receiving a blood transfusion. However, since antibody tests can take up to 6 months to show positive, other screening proceedures (discussed above) have been added to antibody testing. This has reduced the chance of transmission in the blood supply from infected persons who have not yet produced antibodies against HIV.
The above information applies strictly to the American blood supply. I do not know if other countries follow the same protocol. You would have to ask your local blood bank if they do antibody testing for both HIV-1 and HIV-2, and if they do pre-donation interviews and p-24 testing. We do know however that since these screening proceedures have been put into place, the chances of infection with HIV in the American blood supply have been significantly reduced, and the chance of infection with HIV through a blood transfusion in the USA is very small.
If you have any further questions, please feel free to call the Centers for Disease Control at 1.800.232.4636 (Nationwide). Rick Sowadsky MSPH CDS
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