Comparison of pre‐ and post‐bronchodilator lung function as predictors of mortality: The HUNT Study

Abstract

Background and objective Post‐bronchodilator (BD) lung function is recommended for the diagnosis of chronic obstructive pulmonary disease (COPD). However, often only pre‐BD lung function is used in clinical practice or epidemiological studies. We aimed to compare the discrimination ability of pre‐BD and post‐BD lung function to predict all‐cause mortality.

Methods Participants aged ≥40 years with airflow limitation (n = 2538) and COPD (n = 1262) in the second survey of the Nord‐Trøndelag Health Study (HUNT2, 1995–1997) were followed up until 31 December 2015. Survival analysis and time‐dependent area under the receiver operating characteristic curves (AUC) were used to compare the discrimination ability of pre‐BD and post‐BD lung function (percent‐predicted forced expiratory volume in the first second (FEV1) (ppFEV1), FEV1 z‐score, FEV1 quotient (FEV1Q), modified Global Initiative for Chronic Obstructive Lung Disease (GOLD) categories or GOLD grades).

Results Among 2538 participants, 1387 died. The AUC for pre‐BD and post‐BD ppFEV1 to predict mortality were 60.8 and 61.8 (P = 0.005), respectively, at 20 years' follow‐up. The corresponding AUC for FEV1 z‐score were 58.5 and 60.4 (P < 0.001), for FEV1Q were 68.7 and 70.1 (P = 0.002) and for modified GOLD categories were 62.3 and 64.5 (P < 0.001). Among participants with COPD, the AUC for pre‐BD and post‐BD ppFEV1 were 57.0 and 58.8 (P < 0.001), respectively. The corresponding AUC for FEV1 z‐score were 53.1 and 55.8 (P < 0.001), for FEV1Q were 63.6 and 65.1 (P = 0.037) and for GOLD grades were 56.0 and 57.0 (P = 0.268).

Conclusion Mortality was better predicted by post‐BD than by pre‐BD lung function; however, they differed only by a small margin. The discrimination ability using GOLD grades among COPD participants was similar.