Evaluation of diseases´ tests and programmes of screening

Preventive medicine is an important area of health care, mainly in Primary Health Care. Because it is acted on healthy people (in Pediatrics, in healthy children and adolescents), preventive medicine needs even stronger supporting evidence (on benefits, harms and costs) than therapeutic and/or diagnostic interventions. The aim of this article is to present the theoretical concepts related to screening tests and programmes for early diseases detection, with special attention to main potential harm in overdiagnosis (false positive), causing unnecessary anxiety and intervention, and also to screening bias (lead time bias, length bias and compliance). It is interesting to relate preventive medicine with two new concepts (quaternary prevention and cascade effect), because it is important to know the clinical and ethical implications of screening programmes and to achieve an evidence-based decision-making in this outstanding area of health.