Screening Tests

Diagnostic Tests

Purpose

To detect potential disease indicators.

To establish presence/absence of disease.

Target Population

Large numbers of asymptomatic, but potentially ‘at risk’ individuals.

Symptomatic patients to establish diagnosis, or asymptomatic individuals with a positive screening test.

Test Method

Simple, acceptable to patients and staff.

Maybe invasive, expensive but justifiable as necessary to establish diagnosis.

Positive Result Threshold

Generally chose towards high sensitivity not to miss potential disease.

Chosen towards high specificity (true negatives).  More weight given to accuracy and precision than to patient acceptability.

Positive Result

Essentially indicates suspicion of disease (often used in combination with other risk factors) that warrants confirmation.

Result provides a definite diagnosis.

Cost

Cheap, benefits should justify the costs since large numbers of patients will need to be screened to identify a small number of potential cases.

Higher costs associated with diagnostic test maybe justified to establish diagnosis.