Challenge data
Enter the PC20. If a 20% fall was not reached at the highest dose, mark the test negative.
Optional context
Result
Enter the PC20 and press Interpret.
Interpretation categories (ATS/ERS)
| PC20 (mg/mL) | Interpretation |
|---|---|
| > 16 | Normal bronchial responsiveness |
| 4 – 16 | Borderline hyperresponsiveness |
| 1 – 4 | Mild hyperresponsiveness (positive) |
| < 1 | Moderate-to-severe hyperresponsiveness |
PD20 ≈ 1 mg corresponds roughly to PC20 16 mg/mL (a tidal-breathing PD20 > 400 µg makes current symptomatic asthma unlikely). A negative challenge has a high negative predictive value for asthma; positive results are not specific — they also occur in COPD, allergic rhinitis, and after respiratory infections.
Clinical decision support only. Interpretation assumes an acceptable baseline FEV₁ (generally ≥ 60–70% predicted) and a standardized protocol. The clinical value of PC20 depends on pre-test probability. Recent ATS technical standards also express results as PD20 (dose); confirm which metric your laboratory reports. Correlate with the full clinical picture.
References: Coates AL, et al. ERS technical standard on bronchial challenge testing: methacholine. Eur Respir J 2017;49:1601526. · ATS Guidelines for Methacholine and Exercise Challenge Testing, 1999/2000.