Background: The best method for expressing lung function impairment is undecided. We tested in a population of patients with chronic obstructive pulmonary disease (COPD) whether forced expiratory volume in 1 second (FEV1) or FEV1 divided by height squared (FEV1/ht2) was better than FEV1 percent predicted (FEV1PP) for predicting survival.
Method: FEV1, FEV1PP, and FEV1/ht2 recorded post bronchodilator were compared as predictors of survival in 1095 COPD patients followed for 15 years. A staging system for severity of COPD was defined from FEV1/ht2 and compared with the Global Initiative for Obstructive Lung Disease (GOLD) staging system.
Result: FEV1/ht2 was a better univariate predictor of survival in COPD than FEV1 and both were better than FEV1PP. The best multivariate model for predicting survival included FEV1/ht2, age and sex. Comparing the GOLD stages with the FEV1/ht2 groups found that survival was more coherent within each FEV1/ht2 group than it was within each GOLD stage. FEV1/ht2 had 60% more people in its most severe group than the severest GOLD stage with these extra subjects having equivalently poor survival and had 155% more in the least severe group with equivalent survival. GOLD staging misclassified 51% of subjects with regard to survival.
Conclusion: We conclude that GOLD criteria using FEV1PP do not optimally stage COPD with regard to survival. An alternative strategy using FEV1/ht2 improves the staging of this disease. Studies which stratify COPD patients to determine the effect of interventions such as drug trials, rehabilitation, or management guidelines should consider alternatives to the GOLD classification.