[Screening from an epidemiologic perspective].

The concept of screening is that detection of early disease may permit treatment at a more tractable stage and thus improve prospects for survival and prevention of death from the disease. The principle is so suggestive that the issue of screening appears focused on the determination of appropriate imaging tools or biomarkers and translating them into the health care system as rapidly as possible. However, the application of tests to identify precursors or early signs of disease in a largely unaffected population raises problems which have to be well understood to offer effective high-level screening. The present article provides an overview of the basic obstacles and how to cope with them. It turns out that quality assurance of service screening has to be considered not as optional but as a condition sine qua non.