[Screening and early detection in blood transfusion: when are they indicated?].

Screening is proposed to allow an early intervention concerning a diseased individual, but its public health consequences are seldom considered. We propose criteria to judge whether a screening program can be associated to a benefit to patients or society. These criteria refer to the magnitude of disease, the characteristics of the pre-clinical stage, the availability of reliable and valid tests, the effectiveness and risk for all individuals, whether they are diseased or not, and acceptability to the health-care system and to individuals. We illustrate the application of these criteria to screening of human immunodeficiency virus among blood donors, hepatitis among recipients of labile blood products, and bacterial contaminations among febrile recipients. These criteria should be considered in decision analyses including alternatives to screening and all aspects of safety regarding patients and population.