Sensitivity & Specificity
Direct answer: Sensitivity is the true-positive rate; specificity is the true-negative rate. In practice PPV and NPV matter more, because they account for how common the condition is.
The two core measures of diagnostic accuracy — and two more you actually care about in practice.
| Measure | Meaning | What it answers |
|---|---|---|
| Sensitivity | True positive rate | How well does it catch people who DO have the condition? |
| Specificity | True negative rate | How well does it avoid false positives in people who DON'T? |
| PPV | Positive predictive value | If it's positive, how likely is it a true positive? (depends on prevalence) |
| NPV | Negative predictive value | If it's negative, how likely is it a true negative? |
Why PPV/NPV matter
A test with 95% sensitivity and 95% specificity can still give mostly false positives in a low-prevalence population — that's why confirmatory testing and prevalence context matter.
See also rapid test vs PCR and IgG vs IgM.
Frequently Asked Questions
Why do PPV and NPV matter more than sensitivity? They account for how common the condition is — a highly sensitive test can still be mostly wrong in a low-prevalence population.
Related knowledge
References
- CLSI EP17-A2: Evaluation of detection capability. Clinical and Laboratory Standards Institute.
- WHO diagnostic testing guidance (point-of-care and rapid diagnostics).
By Progene Bio Regulatory Affairs Team · Medical Device QA · Medical disclaimer · Last reviewed: 2026-09-12