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Ensuring a safe blood supply requires testing all donations for HIV, although donors constitute a low-prevalence population. False-positive tests are an inevitable consequence in this setting. HIV is diagnosed by detecting antibodies on a screening enzyme immunoassay, which is then confirmed by a Western blot. The FDA recently recommended a less stringent interpretation of the Western blot (no requirement for reactivity to HIV polymerase protein p31), which could increase the number of false-positive results. To evaluate the prevalence of false-positive tests in recent blood donor pools, these authors reviewed a database of 5 million blood donations made to five blood centers between 1991 and 1995.
Four hundred twenty-one (0.008%) donations …