Screening refers to the application of a medical procedure or test to people who as yet have no symptoms of a particular disease, for the purpose of determining their likelihood of having the disease. The screening procedure itself does not diagnose the illness . Those who have a positive result from the screening test will need further evaluation with subsequent diagnostic tests or procedures. The goal of screening is to reduce morbidity or mortality from the disease by detecting diseases in their earliest stages, when treatment is usually more successful. Sensitivity and specificity are measures of a test's ability to correctly classify a person as having a disease or not having a disease.
Sensitivity refers to a test's ability to designate an individual with disease as positive.
A highly sensitive test means that there are few false negative results, and thus fewer cases of disease are missed. The specificity of a test is its ability to designate an individual who does not have a disease as negative. A highly specific test means that there are few false positive results. It may not be feasible to use a test with low specificity for screening, since many people without the disease will screen positive, and potentially receive unnecessary diagnostic procedures. It is desirable to have a test that is both highly sensitive and highly specific.