Consequences of Using Post- or Prebronchodilator Reference Values in Interpreting Spirometry.

Postbronchodilator spirometry is used for the diagnosis of chronic obstructive pulmonary disease. However, prebronchodilator reference values are used for spirometry interpretation. To compare the resulting prevalence rates of abnormal spirometry and study the consequences of using pre- or postbronchodilator reference values generated within SCAPIS (Swedish CArdioPulmonary bioImage Study) when interpreting postbronchodilator spirometry in a general population. SCAPIS reference values for postbronchodilator and prebronchodilator spirometry were based on 10,156 and 1,498 never-smoking, healthy participants, respectively. We studied the associations of abnormal spirometry, defined by using pre- or postbronchodilator reference values, with respiratory burden in the SCAPIS general population (28,851 individuals). Bronchodilation resulted in higher predicted medians and lower limits of normal (LLNs) for FEV/FVC ratios. The prevalence of postbronchodilator FEV/FVC ratio lower than the prebronchodilator LLN was 4.8%, and that of postbronchodilator FEV/FVC lower than the postbronchodilator LLN was 9.9%, for the general population. An additional 5.1% were identified as having an abnormal postbronchodilator FEV/FVC ratio, and this group had more respiratory symptoms, emphysema (13.5% vs. 4.1%;  < 0.001), and self-reported physician-diagnosed chronic obstructive pulmonary disease (2.8% vs. 0.5%,  < 0.001) than subjects with a postbronchodilator FEV/FVC ratio greater than the LLN for both pre- and postbronchodilation. Pre- and postbronchodilator spirometry reference values differ with regard to FEV/FVC ratio. Use of postbronchodilator reference values doubled the population prevalence of airflow obstruction; this was related to a higher respiratory burden. Using postbronchodilator reference values when interpreting postbronchodilator spirometry might enable the identification of individuals with mild disease and be clinically relevant.