FEV₁Q: a race-neutral approach to assessing lung function

Background Forced expiratory volume in 1 s quotient (FEV₁Q) is a simple approach to spirometry interpretation that compares measured lung function to a lower boundary. This study evaluated how well FEV₁Q predicts survival compared with current interpretation methods and whether race impacts FEV₁Q. Methods White and Black adults with complete spirometry and mortality data from the National Health and Nutrition Examination Survey (NHANES) III and the United Network for Organ Sharing (UNOS) database for lung transplant referrals were included. FEV₁Q was calculated as FEV₁ divided by 0.4 L for females or 0.5 L for males. Cumulative distributions of FEV₁ were compared across races. Cox proportional hazards models tested mortality risk from FEV₁Q adjusting for age, sex, height, smoking, income and among UNOS individuals, referral diagnosis. Harrell’s C-statistics were compared between absolute FEV₁, FEV₁Q, FEV₁/height², FEV₁ z-scores and FEV₁ % predicted. Analyses were stratified by race. Results Among 7182 individuals from NHANES III and 7149 from UNOS, 1907 (27%) and 991 (14%), respectively, were Black. The lower boundary FEV₁ values did not differ between Black and White individuals in either population (FEV₁ first percentile difference ≤0.01 L; p>0.05). Decreasing FEV₁Q was associated with increasing hazard ratio (HR) for mortality (NHANES III HR 1.33 (95% CI 1.28–1.39) and UNOS HR 1.18 (95% CI 1.12–1.23)). The associations were not confounded nor modified by race. Discriminative power was highest for FEV₁Q compared with alternative FEV₁ approaches in both Black and White individuals. Conclusions FEV₁Q is an intuitive and simple race-neutral approach to interpreting FEV₁ that predicts survival better than current alternative methods.