Low-Dose CT (LDCT) — Lung Cancer
Test Characteristics
| Metric | Value |
|---|---|
| False-negative rate | 3% (sensitivity 97%) |
| False-positive rate | 4.8% (specificity 95.2%) |
| Bayes factor | 20× |
| Base rate | 2% in high-risk screened populations (heavy smokers aged 50–80) |
Interpreting Results
| Scenario | Prior | + Result | − Result |
|---|---|---|---|
| Heavy smoker in screening program | 2% | 20 × 2% = 40%2%× 2040% | 1/20 × 2% = 0.1%2%÷ 200.1% |
| Smoking + occupational exposure (asbestos, radon) | 5% | 20 × 5% ≥ 100%5%× 20100% | 1/20 × 5% = 0.25%5%÷ 200.25% |
20 × 5% ≥ 100%5%× 20100%: the approximation saturates. Exact posterior (full Bayesian math) is 51%. One of the strongest screening tests available — powerful in both directions.
- + result: risk goes from red hair (2%) to 40%
- − result: risk drops to appendicitis this year (0.1%)
Sources:
- SUMMIT prospective cohort study, 2025. 12-month episode sensitivity in high-risk smoking population.