FEV₁ as a Standalone Spirometric Predictor and the Attributable Fraction for Death in Older Persons

Commonly used thresholds for staging FEV₁ have not been evaluated as standalone spirometric predictors of death in older persons. Specifically, the proportion of deaths attributed to a reduced FEV₁, when staged by commonly used thresholds in L, percent of predicted (% pred), and Z scores, has not been previously reported.

In 4,232 white persons ≥ 65 y old, sampled from the Cardiovascular Health Study, FEV₁ was stratified as stage 1 (FEV₁ ≥ 2.00 L, ≥80% pred, and Z score ≥-1.64), stage 2 (FEV₁ 1.50-1.99 L, 50-79%pred, and Z score -2.55 to -1.63), and stage 3 (FEV₁ < 1.50 L, < 50% pred, and Z score < -2.55). Notably, a Z score threshold of -1.64 defines normal-for-age lung function as the lower limit of normal (ie, 5th percentile of distribution), and accounts for differences in age, sex, height, and ethnicity. Next, adjusted odds ratios and average attributable fractions for 10-y all-cause mortality were calculated, comparing FEV₁ stages 2 and 3 against stage 1, expressed in L, % pred, and Z scores. The average attributable fraction estimates the proportion of deaths attributed to a predictor by combining the prevalence of the predictor with the relative risk of death conferred by that predictor.

FEV₁ stage 2 and 3 in L, % pred, and Z scores yielded similar adjusted odds ratios of death: 1.40-1.51 for stage 2 and 2.35-2.66 for stage 3. Conversely, FEV₁ stages 2 and 3 in L, % pred, and Z scores differed in prevalence: 12.8-28.6% for stage 2 and 6.4-17.5% for stage 3, and also differed in the adjusted average attributable fraction for death: 3.2-6.4% for stage 2 and 4.5-9.1% for stage 3.

In older persons, the proportion of deaths attributed to a reduced FEV₁ is best stratified by Z score staging thresholds because these yield a similar relative risk of death but a more age- and sex-appropriate prevalence of FEV₁ stage.