This article is more than 5 years old. Information may no longer be current.

Lower methacholine challenge test cutoff effective in children

A cutoff of 4 mg/mL or less in the methacholine challenge test would recognize most children suspected of having asthma, according to recent study results.

Researchers at Montreal Children’s Hospital studied the effect of decreasing the methacholine challenge test (MCT) provocative concentration that caused a decrease in forced expiratory volume in 1 second (FEV₁) of 20% (PC₂₀) cutoff from 8 mg/mL to 4 mg/mL. There were 748 patients from 2006 to June 2012 referred by nonrespiratory physicians. Spirometry was used for MCT. A 2-minute tidal breathing dosing protocol was used, and linear interpolation calculated PC₂₀.

There were 134 patients (17.9%; mean age, 12.57 years; 55.9% females) with a negative MCT result (<20% decrease in FEV₁ at a methacholine concentration of 8 mg/mL), while 614 patients (82.1%; mean age, 11.4 years; 55.9% females) responded at 8 mg/mL or less. Of those respondents, 570 patients (92.8%) had a positive MCT of 4 mg/mL or higher (median PC₂₀ of 0.47 mg/mL), while 7.2% of the patients responded at a dose between 4 mg/mL and 8 mg/mL (median PC₂₀ of 6.37 mg/mL).

“There was no difference in the number of positive test results between the sexes, regardless of the cutoff,” the researchers reported.

MCT had a sensitivity of 82.1% at 8 mg/mL cutoff and 76.2% at 4 mg/mL cutoff. In a pretest likelihood of 75%, sensitivity was 92.1% and specificity was 71.2% at 4 mg/mL and 88.7% and 71.2% at 3 mg/mL, respectively.

“The present results support that a cutoff of 4 mg/mL or less would identify most patients suspected of having asthma and exclude only a small percentage of the population suspected of having asthma,” the researchers concluded. “A 10% decrease in FEV₁ at a concentration of 10 mg/mL indicates that the test could be further shortened.”

Disclosure: The researchers report no relevant financial disclosures.