Influence of outdoor temperature and humidity on the methacholine challenge test

Objective of this study was to evaluate whether outdoor temperature and humidity can influence methacholine test results in outpatients living in temperate areas. 4,723 subjects (2,391 males; age: 35.1 ± 16.15; FEV1 = 100.36 % [relative interquartile range (IQR):92.34–108.8]) that performed methacholine tests for suspected asthma between 2000 and 2010 were considered. Outdoor minimum, mean, and maximum temperature values (°C), relative humidity (%), and dew point (T dp), registered when performing the tests, were examined. Airways hyperresponsive patients, with PD20 (provocative dose to obtain a 20 % fall in FEV1)