Anti-TPO — Auto-Immune Hypothyroidism
Test Characteristics
| Metric | Value |
|---|---|
| False-negative rate | 7% (sensitivity 93%) |
| False-positive rate | 5% (specificity 95%) |
| Bayes factor (positive test) | 20× |
| Bayes factor (negative test) | 1/10× |
| Base rate | 5% of US adults |
Interpreting Results
| Scenario | Prior | + Result | − Result |
|---|---|---|---|
| Unselected adult | 5% | 20 × 5% ≥ 100%5%× 20100% | 1/10 × 5% = 0.5%5%÷ 100.5% |
| Woman with fatigue, weight gain, family history | 15% | 20 × 15% ≥ 100%15%× 20100% | 1/10 × 15% = 1.5%15%÷ 101.5% |
| Already diagnosed hypothyroid (etiology?) | 50% | 20 × 50% ≥ 100%50%× 20100% | 1/10 × 50% = 5%50%÷ 105% |
20 × 5% ≥ 100%5%× 20100%: exact posterior is 51%. 20 × 15% ≥ 100%15%× 20100%: exact posterior is 78%. 20 × 50% ≥ 100%50%× 20100%: exact posterior is 95%. Strong rule-in (20×) confirms autoimmune etiology. Good rule-out (1/10×) — a negative anti-TPO makes Hashimoto's unlikely but does not exclude it entirely (~5-10% of Hashimoto's patients are seronegative). Anti-TPO positivity can precede clinical hypothyroidism by years.
- + result: risk goes from vegetarian (5%) to 51%
- − result: risk drops to identical twin (0.5%)
Sources:
- StatPearls. Hashimoto Thyroiditis.
- Systematic review, Frontiers in Public Health, 2022. PMC 9608544.