What is the role of methacholine challenge testing in the evaluation of pediatric asthma?

Updated: Jan 08, 2019
  • Author: Girish D Sharma, MD, FCCP, FAAP; Chief Editor: Kenan Haver, MD  more...
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The degree of airway responsiveness can be assessed by methacholine challenge testing. [43] Methacholine causes bronchoconstriction via muscarinic acetylcholine receptor M3, and the resultant decrease in FEV1 is recorded by spirometry. The test can help to confirm the diagnosis of asthma in a patient with history of asthma but normal spirometry findings.

During the test, the patient inhales increasing concentrations of methacholine aerosol via a nebulizer; spirometry is performed before and after each dose. A positive response is a 20% fall in FEV1. The corresponding concentration of methacholine (mg/mL) is called PC 20 . A PC 20 of greater than 16 mg/mL indicates normal bronchial responsiveness. PC 20 values of 4-16 mg/mL, 1-4 mg/mL, and < 1 mg/mL indicate borderline, mild, and moderate-to-severe bronchial hyperresponsiveness, respectively.

Methacholine challenge testing is more useful in excluding a diagnosis of asthma than in establishing one because its negative predictive power is greater than its positive predictive power. [43] Other agents (ie, histamine, mannitol) are also used for bronchoprovocation.

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