PSA — Prostate Cancer
Test Characteristics
| Metric | Value |
|---|---|
| False-negative rate | 7% (sensitivity 93%) |
| False-positive rate | 80% (specificity 20%) |
| Bayes factor (positive test) | 1.5× |
| Bayes factor (negative test) | 1/3× |
| Base rate | 5% of men aged 55–69 undergoing screening |
Interpreting Results
| Scenario | Prior | + Result | − Result |
|---|---|---|---|
| Average screening male aged 55–69 | 5% | 1.5 × 5% = 7.5%5%× 1.57.5% | 1/3 × 5% = 1.7%5%÷ 31.7% |
| African American or strong family history | 10% | 1.5 × 10% = 15%10%× 1.515% | 1/3 × 10% = 3.3%10%÷ 33.3% |
Nearly uninformative in both directions. A positive barely budges the prior; a negative offers only modest reassurance. Most false positives come from BPH. High sensitivity alone does not make a useful test.
- + result: risk barely moves — from vegetarian (5%) to 7.5%
- − result: nearly useless in either direction
Sources:
- BMC Medicine systematic review and meta-analysis, 2022. PSA ≥4.0 ng/mL cutoff.
- USPSTF. Prostate cancer screening recommendation.