Methacholine Challenge Interpretation
Reads a methacholine challenge against the published cutpoints for whichever metric was reported.
Open the calculator → Runs in your browser. Data leaves only if you deliberately send a problem report from the interactive tool.
Example
- Which metric was reported
- PD20, the dose in micrograms (the 2017 standard)
- The reported value, in micrograms for PD20 or mg/mL for PC20
- 50
Result: a PD20 of 50 micrograms is mild bronchial hyperresponsiveness
The tool opens with these values already filled in. Replace them with your own.
What the result means
- PD20, the 2017 metric
- Above 400 micrograms normal, 100 to 400 borderline, 25 to 100 mild bronchial hyperresponsiveness, below 25 moderate to severe.
- PC20, the legacy metric
- Above 16 mg/mL normal, 4 to 16 borderline, 1 to 4 mild, below 1 moderate to severe.
- Why dose, not concentration
- A concentration depends on the nebulizer output and the inhalation protocol, so a PC20 from one laboratory is not comparable with a PC20 from another. A delivered dose is.
- A negative test
- The informative one. Its negative predictive value for current symptomatic asthma is high, and that is the main reason the challenge is done.
- A positive test
- Does not diagnose asthma on its own. Bronchial hyperresponsiveness also occurs in allergic rhinitis, in COPD, after a viral infection, and in smokers.
- A falsely negative test
- Usually a medication that was not withheld. Inhaled corticosteroids, bronchodilators, antihistamines and caffeine all blunt the response.
What you enter
- Which metric was reported
- The reported value, in micrograms for PD20 or mg/mL for PC20
- Medications were withheld for the required intervals (a negative result depends on this)
How this is calculated
Coates AL, Wanger J, Cockcroft DW, et al. ERS technical standard on bronchial challenge testing: general considerations and performance of methacholine challenge tests. Eur Respir J. 2017;49(5):1601526. Read the source ↗
A reference and educational tool. Not medical, legal, or financial advice, and not a substitute for clinician judgment.