Dr. Fuchs and colleagues advocate the use of a particular surrogate marker, neopterin, to protect recipients of blood products from infection. The usefulness of any test depends, in part, on its sensitivity, specificity, and costs. Evaluating a test's performance in detecting an unrecognized pathogen is complicated by the lack of a validated standard for the infection's presence or absence. In the case of testing blood products, costs include those related to discarding blood that would otherwise have been used, needing to find new donors, and implementing the test. If a donor notification program is used, additional emotional and medical costs would be incurred by those donors positive for the surrogate marker.

Surrogate markers to prevent known diseases, such as the use of alanine aminotransferase and antibody to hepatitis B core antigen to prevent post-transfusion hepatitis, can be effective in reducing the transmission of transfusion-associated infections. Specific screening tests, however, such as those for hepatitis C antibody for post-transfusion hepatitis, are more effective than surrogate markers at diminishing the risk for infection from transfusions^[11]. To warrant adoption, testing for surrogate markers should be clinically validated and superior to alternative methods to reduce transfusion-associated disease [2]. If a new pathogen had a similar transmission pattern as human immunodeficiency virus, current donor deferral methods could decrease the number of infected persons who donate by 98% [3]. Treatment of blood products to inactivate viruses is under evaluation [4].

Health professionals should continually seek ways to make therapeutic interventions safer and to balance the risks and benefits of the therapies. At present, the benefits from transfusions in preventing appreciable mortality from anemia far outweigh their risks. When and if these risks are altered, the rule of thumb described in our editorial [5] can be adapted to reformulate transfusion recommendations.