Prevalence of Human Immunodeficiency Virus Type 1 p24 Antigen in U.S. Blood Donors — An Assessment of the Efficacy of Testing in Donor Screening

We performed a multicenter study in 1989 to determine whether screening whole-blood donors for human immunodeficiency virus type 1 (HIV-1) p24 antigen would improve transfusion safety by identifying carriers of the virus who are seronegative for HIV-1 antibody. More than 500,000 donations were tested at 13 U.S. blood centers with test kits from two manufacturers. Units found repeatedly reactive were retested in a central laboratory; if the results were positive, they were confirmed by a neutralization assay. A subgroup of units was also tested for HIV-1 by the polymerase chain reaction. Selected donors confirmed or not confirmed as having p24 antigen were contacted for follow-up interviews to identify risk factors and undergo retesting for HIV-1 markers. Positive tests for p24 antigen were confirmed by neutralization in five donors (0.001 percent of all donations tested), all of whom were also positive for HIV-1 antibody and HIV-1 by polymerase chain reaction. Three of the antigen-positive donors had other markers of infectious disease that would have resulted in the exclusion of their blood; two had risk factors for HIV-1 that should have led to self-exclusion. Of 220 blood units with repeatedly reactive p24 antigen whose presence could not be confirmed by neutralization (0.04 percent of the donations studied), none were positive for HIV-1 antibody, HIV-1 by polymerase chain reaction (120 units tested), or virus culture (76 units tested) — attesting to the specificity of confirmatory neutralization. The finding that no donation studied was positive for p24 antigen and negative for HIV-1 antibody suggests that screening donors for p24 antigen with tests of the current level of sensitivity would not add substantially to the safety of the U.S. blood supply. (N Engl J Med 1990; 323:1312–7.) THE combination of donor education and self-exclusion with serologic testing has proved very effective in reducing the incidence of infection with human immunodeficiency virus type 1 (HIV-1) as a result of transmission by transfusion.^1,2 There is a residual risk, however, because of the prolonged interval between infection and seroconversion³ and because some donors with recent infections may not report or may not perceive the high risk of the behavior that resulted in their exposure.⁴ The current risk of HIV transmission from screened blood is not known, but it has been estimated to range from 1 in 38,000 to 1 in.