Bronchoprovocation testing with methacholine is used to determine bronchial hyperresponsiveness in United States Marine Corps (USMC) recruits suspected to have asthma. We recently modified our methacholine challenge testing (MCT) protocol by lowering the maximum final PC20 concentration from 25 to 16 mg/ml to reflect the current American Thoracic Society guidelines. We hypothesized that lowering the maximum concentration would decrease the number of recruits diagnosed with airway hyperresponsiveness and thereby increase recruit graduation rates.
A retrospective chart review was performed on all MCTs completed by USMC recruits referred for possible asthma during a two-year period to compare the percentage of positive methacholine challenge tests. If the initial methacholine challenge was negative, subsequent graduation rates were determined and compared.
The percentage of positive methacholine challenge tests did not change after switching to a lower dose protocol (48.0% versus 45.1%, p=0.773). The overall graduation rate for recruits who had a negative methacholine challenge was significantly higher in high dose protocol compared to low dose protocol (85.4 % versus 53.3%, p=0.002) although no recruit who had a negative methacholine challenge with the low dose protocol was subsequently diagnosed with asthma during the remainder of recruit training.
Modifying the methacholine challenge protocol to lower the maximum PC20 concentration did not change overall short-term retention as measured by completion of recruit training.
This study suggests that a methacholine challenge protocol with a maximum concentration of 16 mg/ml can be safely administered without a significant false negative result. 2001 (HDP)2002 (LDP)DifferenceSubjects referred for asthma who completed MCT10688P = 0.1951Age (years)19.0 +/− 1.4219.4 +/− 1.82P = 0.1043Subjects with positive MCT51 (48.1%)40 (45.5%)P = 0.7731Mean PC20 (mg/ml)11.1 +/− 10.127.1 +/− 5.92P = 0.0743Negative MCT separated for asthma1 (2.1%)0P = 1.001Negative MCT and successful graduation41 (85.4%)16 (53%)P = 0.0021Negative MCT separated for non-asthma conditions6 (12.5%)14 (46%)P = 0.00111 = Calculated with Fisher’s exact test2 = Calculated as mean +/− standard deviation3 = Calculated with rank sum test
C.M. Stafford, None.