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Effect of lowering methacholine challenge test cutoff in children
1Division of Pediatric Respiratory Medicine, Montreal Children's Hospital, McGill University Health Centre, Montreal, Quebec, Canada.
Insights
Lowering the methacholine challenge test (MCT) provocation concentration (PC20) cutoff to 4 mg/mL for pediatric asthma diagnosis is effective. This change maintains high sensitivity and accurately identifies asthma in children.
Area of Science:
- Pediatric Pulmonology
- Respiratory Medicine
- Clinical Diagnostics
Background:
- Asthma diagnosis relies on clinical judgment, atopy history, and methacholine challenge testing (MCT).
- Current guidelines recommend a provocation concentration (PC20) of 4 mg/mL for a positive MCT result.
Purpose of the Study:
- To evaluate the impact of reducing the MCT PC20 cutoff from 8 mg/mL to 4 mg/mL.
- To assess changes in positive test result counts and result distribution.
Main Methods:
- Retrospective study at Montreal Children's Hospital (2006-2012).
- Included patients referred by nonrespiratory physicians.
- Utilized a 2-minute tidal breathing protocol with linear interpolation for PC20 calculation.
Main Results:
- 748 pediatric patients underwent spirometry and MCT.
- A PC20 cutoff of 4 mg/mL yielded a sensitivity of 76.2%.
- This cutoff excluded only 5.8% of referred patients, with 7.2% testing positive at ≤8 mg/mL.
Conclusions:
- A PC20 cutoff of 4 mg/mL is a reasonable and effective threshold for diagnosing asthma in children.
- This cutoff demonstrates good sensitivity and minimal exclusion of suspected cases in a pediatric referral population.
Background:
The diagnosis of asthma is based on clinical judgment, history of personal or familial atopy, and testing, typically with a methacholine challenge test (MCT). Guidelines suggest a provocation concentration that caused a decrease in forced expiratory volume in 1 second of 20% (PC20) cutoff of 4 mg/mL for a positive test result.
Objective:
To investigate the effect of lowering the MCT PC20 cutoff from 8 to 4 mg/mL on the number of positive test results and the distribution of test results.
Methods:
A retrospective study was conducted at the Montreal Children's Hospital from January 1, 2006, through June 31, 2012, on patients referred by nonrespiratory physicians. A 2-minute tidal breathing dosing protocol was used, and the PC20 was calculated by linear interpolation.
Results:
A total of 748 patients were tested using spirometry. A total of 134 (17.9%) had a negative MCT result, and 614 (81.1%) responded at 8 mg/mL or less. A total of 570 patients (92.8% of respondents) responded at a dose of 4 mg/mL or higher (median PC20 of 0.47 mg/mL), with the remainder (7.2% of respondents) responding at a dose between 4 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 cutoff. The sensitivity of MCT was 82.1% at a cutoff of 8 mg/mL and 76.2% at 4 mg/mL. With a pretest likelihood of asthma of 75%, the specificity was 71.2%.
Conclusion:
In a standard pediatric referral population, using a PC20 cutoff of 4 mg/mL provided a sensitivity of 76.2%, and only excluded 5.8% of all those referred for suspicion of asthma (7.2% of all test results were ≤8 mg/mL). This finding suggests that a PC20 of 4 mg/mL can reasonably be used as a cutoff for a positive MCT result in children.
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