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Microbiological screening of blood donations: cost versus effectiveness.

The already considerable list of pre-transfusion microbial screening tests may well increase. Some American opinion favours attempting to achieve a 'zero-risk' blood supply by introducing extra tests. However, as well as being theoretically unattainable, 'zero-risk' causes practical problems as the efficacy of a screening test is often predicted, not proven. The increasing complexity of extra testing can overload the system, causing laboratory and clerical errors, and although the blood supply must be as safe as possible a small residual risk should be anticipated and balanced against the risk of withholding transfusion. Assessing cost-effectiveness requires that indirect and direct consequences of infecting a recipient are considered. What is cost-effective in one country may not be elsewhere, due to factors such as microbial prevalence. Uniformity of worldwide transfusion policy must be balanced against the best local use of increasingly limited health-care budgets.