118. Pulm PEEPs Pearls: Methacholine Challenge

Furf and Monty are back with another Pulm PEEPs Pearls episode. The topic of today’s discussion is an often discussed, but often misunderstood, test; the methacholine challenge. They’ll review when to utilize this test, how it should be performed, and the appropriate interpretation.

Contributors

This episode was prepared with research by Pulm PEEPs Associate Editor George Doumat.

Dustin Latimer, another Pulm PEEPs Associate Editor, assisted with audio and video editing.

Key Learning Points

What the Test Measures

Methacholine challenge is a direct bronchial provocation test of airway hyperresponsiveness (AHR), a core physiologic feature of asthma.

Anyone will bronchoconstrict at high enough concentrations — the test looks for an abnormal threshold.

The key endpoint is the PC20: the methacholine concentration causing a 20% fall in FEV1.

Abnormal in adults: PC20 ≤ 8–16 mg/mL

Test Performance

Meta-analyses: pooled sensitivity ~60%, specificity ~90%.