How are results of methacholine challenge testing interpreted?

Updated: May 14, 2020
  • Author: Kevin McCarthy, RPFT; Chief Editor: Nader Kamangar, MD, FACP, FCCP, FCCM  more...
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A 20% fall in FEV1 generally is considered a positive test. The American Thoracic Society recommends the use of a 35% fall specific airway conductance (SGaw) to denote the presence of airway hyperreactivity when technically good spirometry cannot be obtained. It has been suggested that a significant subset of patients will exhibit a 35% fall in SGaw when the FEV1 remains greater than 80% of its baseline value. This may represent a subset of patients that has widespread small airway changes.

One scheme for using the PC20 FEV1 to characterize the severity of clinical hyperreactivity has been used by Hargreave et al. PC20 FEV1 severity is assessed as follows: 0.03-0.124 is considered severe, 0.125-1.99 is considered moderate, 2.00-7.99 is considered mild, and 8-25 is considered an increased hyperresponsive reaction (however, clinically significant disease is not common).

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