Screening is a way of identifying people at increased or greater risk for a condition, although they do not yet have any signs or symptoms. In some cases, mass screening-screening large numbers of people -is appropriate, for example in the past for tuberculosis. In other cases, only those with high risk factors, like a family history of conditions such as cancer and diabetes, are screened. However, there are a number of problems with screening. There are always false negatives, cases where a patient has a disease but screening does not identify it. There are also false positives, where someone is told they have a disease when in fact they do not. Furthermore, with some diseases, early identification is of no benefit to the patient as there is no treatment available.

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