History of medical screening: from concepts to action.

The objective of medical screening is to identify disease in its preclinical, and therefore hopefully still curable, phase. This may have been an old quest in medicine but it became historically possible when at least four conditions were met: the availability of simple, valid and acceptable forms of tests, the discovery of effective treatments, the establishment of a theory of screening, and the wide access to health care. Five selected examples that illustrate the history of medical screening are reviewed: screening for psychiatric disorders in the United States army as it is one of the oldest screening programmes; screening for syphilis as it used one of the earliest screening tests; screening for diabetes as one of the first modern forms of mass screening; screening for cervical cancer using the Pap test as one of the greatest successes of screening; and screening for breast cancer by mammography as this offers a good opportunity to discuss the development of modern evaluation of screening programmes. The evaluation of the impact of screening on human health slowly progressed, from obvious changes in the vital statistics such as the decline in incidence of syphilis, to less obvious changes such as the decline in mortality of cancer of the uterus, to finally more subtle changes, such as the impact of mammographic screening on breast cancer mortality. Methods of evaluation had therefore to adapt, evolving from simple surveys to case-control studies and randomised trials. The history of screening is short, but very rich and mostly still to be written.