QuantiFERON-TB Gold — Latent Tuberculosis
Test Characteristics
| Metric | Value |
|---|---|
| False-negative rate | 5% (sensitivity 95%) |
| False-positive rate | 3% (specificity 97%) |
| Bayes factor (positive test) | 20× |
| Bayes factor (negative test) | 1/20× |
| Base rate | 5% of US population |
Interpreting Results
| Scenario | Prior | + Result | − Result |
|---|---|---|---|
| Mixed primary care panel | 5% | 20 × 5% ≥ 100%5%× 20100% | 1/20 × 5% = 0.25%5%÷ 200.25% |
| US-born healthcare worker | 1% | 20 × 1% = 20%1%× 2020% | 1/20 × 1% = 0.05%1%÷ 200.05% |
| Foreign-born or known TB contact | 20% | 20 × 20% ≥ 100%20%× 20100% | 1/20 × 20% = 1%20%÷ 201% |
20 × 5% ≥ 100%5%× 20100%: exact posterior is 51%. 20 × 20% ≥ 100%20%× 20100%: exact posterior is 83%. Strong in both directions. A negative result in a low-risk healthcare worker (1% prior) drops risk to near zero. A positive result in a foreign-born patient is highly confirmatory. False positives can occur with nontuberculous mycobacteria (NTM). Sensitivity may be reduced in immunocompromised patients.
- + result: risk goes from vegetarian (5%) to 51%
- − result: risk drops to near identical twin (0.25%)
Sources:
- Systematic review and meta-analysis, Clinical Infectious Diseases, 2021. PMC 8423471.
- Systematic review and meta-analysis, BMC Infectious Diseases, 2023. Springer.
- USPSTF. Latent tuberculosis infection screening.