PURPOSE: The American Thoracic Society statement on methacholine challenge testing in asthma recommends two techniques for administration of methacholine, the 2-min tidal breathing (2MTB) method and 5-breath dosimeter (5BD) method, stating they give similar results. This study was performed to determine if there is a difference in rates of diagnosis of asthma between these 2 methods.
METHODS: Data was obtained utilizing a large pulmonary function database from a large urban medical center, and 3 suburban pulmonary clinics. The 5BD method was utilized from January 1, 2005 through December 31, 2006, and the 2MTB method was utilized for the period of January 1, 2007 through December 31, 2007.
RESULTS: 708 subjects underwent methacholine challenge testing during the 3 year study period. 471 subjects (66.5%) underwent the 5BD method and 237 subjects (33.5%) underwent the 2MTB method. 20.8% of the subjects tested with the 5BD method and 30.4% of those tested with the 2MTB method had a PC20<= 8 mg/ml (OR 1.66, 95% CI 1.16 to 2.37, p=0.0049), meeting the ATS criteria of a positive test. The ability to reliably exclude asthma (PC20 > 16 mg/ml) was also altered by the technique used. Using the 5BD method, 71.1% of subjects would have been ruled out for asthma, while only 56.5% of subjects would have been ruled out with the 2MTB technique (p=0.0001).
CONCLUSION: The two protocols recommended by the ATS guidelines are not equivalent. This study showed a difference in the rates of asthma diagnosis at all dosing concentrations of methacholine recommended by the ATS statement, including the group the ATS defined as having strong confirmation of asthma (PC20 <= 1 mg/ml), as well as the group that does not currently have asthma (PC20 > 16 mg/ml).
CLINICAL IMPLICATIONS: Methacholine challenge testing utilizing the 2-min tidal breathing method when compared to the 5-breath dosimeter method, will increase the asthma diagnosis rates as defined by ATS criteria.
DISCLOSURE: Imad Obeid, No Financial Disclosure Information; No Product/Research Disclosure Information