Sensitivity is how well a test catches true cases; specificity is how well it rules out those without the condition. Together they describe a test’s accuracy.
Sensitivity: catching true positives
A highly sensitive test rarely misses people who have the condition. High sensitivity means few false negatives – useful for screening, where you don’t want to miss anyone.
Specificity: ruling out true negatives
A highly specific test rarely flags people who don’t have the condition. High specificity means few false positives – useful for confirming a diagnosis.
The trade-off
Tuning a test to catch more true cases can produce more false alarms, and vice versa. Screening tests favor sensitivity; confirmatory tests favor specificity.
Why it matters for you
A positive screening result often needs a more specific follow-up test to confirm. That two-step design is intentional, not a mistake.
FAQ
What’s the difference between sensitivity and specificity?
Sensitivity measures how well a test finds true cases (few false negatives); specificity measures how well it clears those without the condition (few false positives).
Which matters more?
It depends on the goal. Screening prioritizes sensitivity; confirming a diagnosis prioritizes specificity.
Why did my screening test need a confirmatory test?
Screening tests favor sensitivity and can produce false positives, so a more specific test confirms the result.
This article is educational and not a substitute for medical advice.