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

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.

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 (FEV₁ Q), modified Global Initiative for Chronic Obstructive Lung Disease (GOLD) categories or GOLD grades).

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 FEV₁ Q 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 FEV₁ Q were 63.6 and 65.1 (P = 0.037) and for GOLD grades were 56.0 and 57.0 (P = 0.268).

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.