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Methacholine Challenge Testing*

Comparison of the Two American Thoracic Society-Recommended Methods

From the Pulmonary Division, Department of Pediatrics (Drs. Wubbel, Chesrown, and Hendeles), College of Medicine; the Asthma Research Laboratory, College of Pharmacy (Dr. Asmus); and the Department of Statistics (Dr. Stevens), University of Florida, Gainesville, FL.

Correspondence to: Catherine Wubbel, MD, DeVos Children’s Hospital, 330 Barclay, Suite 200, Grand Rapids, MI 49503; e-mail: Catherine.wubbel{at}spectrum-health.org

Study objectives: Recent American Thoracic Society guidelines recommend two different methods of methacholine challenge testing: the 2-min tidal breathing method with twofold increases in concentration, and the five-breath dosimeter method with fourfold increases. Since the tidal breathing method delivers more methacholine to the mouthpiece, we hypothesized that the provocative concentration of methacholine required to decrease FEV₁ by 20% (PC₂₀) would be lower than with the dosimeter method.

Design: Twelve subjects 18 to 45 years old with stable asthma were selected on the basis of a screening PC₂₀ (by tidal breathing) of < 1 mg/mL, 1 to 4 mg/mL, or 4 to 16 mg/mL (4 subjects in each concentration range). On subsequent visits within a 7-day period, methacholine challenge testing with tidal breathing or dosimeter were performed on separate days, in a randomized crossover manner.

Results: The geometric mean PC₂₀ was 1.8 mg/mL (95% confidence interval [CI], 0.7 to 4.3) after tidal breathing and 1.6 mg/mL (95% CI, 0.7 to 3.7) after dosimeter (p = 0.2). There was no significant difference between the screening PC₂₀ and the PC₂₀ obtained by either method on randomized study days. The maximum decrease in FEV₁ from diluent baseline after the last concentration was 27.8% (range, 20 to 50%) during tidal breathing and 27.9% (range, 16 to 47%) during the dosimeter method (p = 0.35).

Conclusions: Both methods give similar results. Fourfold increases in methacholine concentration with the dosimeter method are as safe as twofold increases with the tidal breathing method.

Key Words: asthma • bronchial challenge • bronchoprovocation • dosimeter • methacholine

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