Morrison defines screening as follows: “Screening for disease is the examination of asymptomatic people in order to classify them as likely or unlikely to have the disease that is the object of screening. People who appear likely to have a disease are investigated further to arrive at a final diagnosis. Those people who are found to have the disease are then treated.”
In other words, screening is not part of general preventive healthcare: It is always directed at a specific disease. The target group consists of people who have not been diagnosed with a disease and are not suspected of having a disease.
Screening normally involves two stages: Following a test that is as sensitive as possible but not necessarily specific, individuals are divided into those who have tested negative and those who have tested positive. Those who have tested positive then undergo a confirmation test that is as specific as possible. This allows the disease to be either diagnosed or ruled out. This confirmation test identifies diseased (true positive) and healthy (false positive) persons.
Key Messages
• The principle behind screening is to achieve earlier diagnosis in as many patients as possible. This is aimed at improving individual prognosis and lowering the overall mortality rate.
• Important components of a screening program are type of invitation, examination procedure, age range, and frequency of screening.
• Diseases that are suitable for screening are common or serious, have a long preclinical phase, and have a significantly better prognosis if diagnosed early.
• The benefit of a screening program, e.g. reduced mortality, should be demonstrated before the program is introduced. Essentially this requires a controlled study with an appropriate comparison group.
• Good counseling provides information and allows those entitled to screening to decide whether or not to undergo it without being put under any pressure.
Source: Spix C, Blettner M. Screening: part 19 of a series on evaluation of scientific publications. Dtsch Arztebl Int. 2012;109(21):385-390. doi:10.3238/arztebl.2012.0385