Seasons can influence the results of the methacholine challenge test

ABSTRACT

This study tried to evaluate whether a methacholine test may be influenced by the seasons. We considered 4826 consecutive subjects with normal spirometry [50.53% males; age 35.1 +/- 16.2; forced expiratory volume in one second 99.5 +/- 13.0%] who underwent a methacholine test for suspected asthma symptoms between 2000 and 2010. They were subdivided into four groups, like the seasons, according to the test dates. A total of 1981 [41%] resulted normal [no PD [20] was obtained with 2400 micro g of methacholine]; the others showed a mean LogPD[20] of 2.52 +/- 0.5 micro g. The number of subjects with bronchial hyper-responsiveness [BHR] found in autumn [789, 62.3%] was higher than in summer [583, 56.7%; P=0.03]. A higher number of females and overweight/obese subjects showed a BHR in autumn compared with the other seasons. The spring mean LogPD[20] value [2.48 +/- 0.48 micro g] was lower if compared with the one measured in summer [2.59 +/- 0.49 micro g; P=0.05]. LogPD 20 value was lower in females and non-smokers in spring compared with summer [P<0.05]. Overweight/obese non-smokers showed a lower LogPD[20] in spring and autumn compared with that in summer [P<0.05]. Autumn was a risk factor [OR 1.378; P=0.001] for BHR [using a PD [20] <2 400 micro g as BHR limit], while spring [OR 1.330; P=0.021] and autumn [OR 1.331; P=0.020] were risk factors for a more severe BHR [using a PD[20] <400 micro g as BHR limit]. There was a higher probability of finding BHR in outpatients with suspected asthma in autumn and spring compared with summer. Spring is the season where BHR may be more severe. Females and overweight/obese subjects were those mainly involved in this seasonal variability of BHR