Categorisation of airway response to methacholine
| PD20 μmol (μg) | PC20 mg·mL−1 | Interpretation |
| >2 (>400) | >16 | Normal |
| 0.5–2.0 (100–400) | 4–16 | Borderline AHR |
| 0.13–0.5 (25–100) | 1–4 | Mild AHR |
| 0.03–0.13 (6–25) | 0.25–1 | Moderate AHR |
| <0.03 (<6) | <0.25 | Marked AHR |
PD20: provocative dose causing a 20% fall in forced expiratory volume in 1 s (FEV1); PC20: provocative concentration causing a 20% fall in FEV1; AHR: airway hyperresponsiveness. Information from [3].