How do screening tests differ from diagnostic tests in epidemiology?

• A. Screening tests are used to confirm disease in symptomatic individuals.
• B. Diagnostic tests are used to screen asymptomatic people.
• C. Screening identifies asymptomatic individuals at risk; diagnostic testing confirms disease in symptomatic individuals or those with positive screening.
• D. Screening results are always definitive.

Answer: (D)

The main idea here is how screening and diagnostic tests serve different purposes and what their results imply. Screening tests are applied to large groups, often people without symptoms, to flag individuals who may have the disease so they can receive further evaluation. Because the goal is to catch as many true cases as possible, screening tests are designed to be highly sensitive, which unavoidably raises the chance of false positives. Diagnostic tests come into play after a screening result is positive or when there’s clinical suspicion; they are used to determine definitively whether disease is present, so they emphasize high specificity to minimize false positives and provide a confirmed diagnosis.

So, the best description is that screening identifies asymptomatic individuals at risk, and diagnostic testing confirms disease in those who have a positive screen or who show symptoms. Screening results are not always definitive—no test is 100% accurate, and false positives and false negatives can occur.