How should a positive bronchodilator test be interpreted?

Bronchodilator testing (BDT) is crucial to establish the reversibility of bronchial obstruction and/or the presence of bronchial hyperresponsiveness (BHR). BDT is considered positive, based on the 2005 ATS/ERS guideline, when there is an absolute and relative change in FEV1 and FVC ≥200 mL in absolute and ≥12% in percentage value. In contrast, the 2021 ATS/ERS guideline determines that BDT is positive if a change >10% of the theoretical FEV1 or FVC value is observed. The aim of the study was to establish which BDT interpretation option correlates best with the presence of BHR confirmed from a methacholine test(MT). Retrospective descriptive and cross-sectional study was designed in adults (18-75 years), in whom a nonspecific bronchoprovocation test with methacholine was done on suspicion of asthma, between 01/02/2018-31/12/2022. Sociodemographic data, MT, targeted therapy at the time of the test and lung function with BDT based on both interpretations were collected. Statistical analysis of quantitative variables was made with the mean and standard deviation (if normally distributed) or the median (if non-normally distributed). Qualitative variables with frequency and percentage. Comparative study between the percentages of the groups of patients was made using X² tests and fisher's test and the concordance study using the kappa test. 845 patients were studied of whom 73% had a positive MT. The BDT was positive according to 2005 criteria in 67% of MT positive and in 33% of MT negative patients. While in the 2021 criteria it was positive in 65% of MT positive and 35% of MT negative patients. The kappa index was 0.82. There is good concordance between the two methods for establishing BDT positivity based on the degree of BHR.