screening

Screening is a process in healthcare and public health that seeks to identify individuals who are at risk of, or who have, a particular disease or condition but who do not yet show overt symptoms. The aim is to detect disease earlier, when intervention can be more effective, and to reduce morbidity and mortality. Screening differs from diagnostic testing, which is performed for people with symptoms or known risk factors.

Screening involves selecting a target population, applying a screening test with certain sensitivity and specificity, and referring those with positive results for definitive diagnostic testing. The interpretation of results depends on test performance, disease prevalence, and the balance of potential benefits and harms. Important concepts include false positives, false negatives, lead time, overdiagnosis, and the cascade of follow-up tests.

Medical screening covers programs and individual decisions. Examples include newborn screening for metabolic disorders, mammography for breast cancer, Pap tests for cervical cancer, and colon cancer screening with fecal tests or colonoscopy. Screening can be population-wide or opportunistic, and intervals are guided by guidelines and resource considerations.

Public health programs assess population benefit, cost-effectiveness, and potential harms. Criteria, such as those proposed by Wilson and Jungner, emphasize disease burden, availability of acceptable tests and treatments, and the balance of benefits to harms. Ethical issues include informed consent, privacy, and equity.

Screening also occurs outside medicine, such as security screening at airports or workplaces, background checks for employment, and environmental screenings for contaminants. Across settings, the effectiveness of screening depends on appropriate test selection, follow-up capacity, and integration with diagnostic verification and care.