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Will human immunodeficiency virus p24 antigen screening increase the safety of the blood supply and, if so, at what cost?

In the “good old days,” the infectious risks of blood transfusions could be measured. Investigators simply enrolled a cohort of several hundred transfusion recipients and observed them for evidence of infection or clinical disease. The performance characteristics of proposed new donor screening tests could also be evaluated directly by testing of a reasonable number of donations (e.g., 5,000 to l0,OOO) by current procedures and by the test under evaluation. If the new test picked up a significant number of infected donations that were missed by the existing procedures and if it had acceptable specificity, then licensure and implementation of the new test was generally warranted. Fortunately for patients, the “good old days” are long gone. With the discovery of human immunodeficiency virus (HIV), human T-lymphotropic virus, and hepatitis C virus, and with the implementation of progressively improved donor selection and testing procedures, the risk of infection via blood transfusions has declined dramatically over the past decade. Risk estimates for the major transfusion-transmitted viruses are now expressed as the number of cases per million units transfused, rather than as a percentage of transfused patients infected.’ Ironically, for those involved in estimating residual risk and in evaluating measures to further reduce risk, the decline in risk has led to an exponential increase in the complexity of the calculation. In response to this dilemma, alternative strategies for estimating residual risks and for projecting incremental yields of proposed new tests have been developed. These approaches involve models that incorporate data on seroconversion window periods and infectious disease incidence in donors, as well as extrapolations from test performance data in nondonor and nonUnited States settings. It is important that blood bankers become familiar with these approaches, since they will be the basis for major policy decisions in the years ahead. The utility of screening donors for HIV type 1 (HIV-I)