A new staging strategy for chronic obstructive pulmonary disease

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 (FEV(1)) or FEV(1) divided by height squared (FEV(1)/ht(2)) was better than FEV(1) percent predicted (FEV(1)PP) for predicting survival. METHOD: FEV(1), FEV(1)PP, and FEV(1)/ht(2) 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 FEV(1)/ht(2) and compared with the Global Initiative for Obstructive Lung Disease (GOLD) staging system. RESULT: FEV(1)/ht(2) was a better univariate predictor of survival in COPD than FEV(1) and both were better than FEV(1)PP. The best multivariate model for predicting survival included FEV(1)/ht(2), age and sex. Comparing the GOLD stages with the FEV(1)/ht(2) groups found that survival was more coherent within each FEV(1)/ht group than it was within each GOLD stage. FEV(1)/ht(2) 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 FEV(1)PP do not optimally stage COPD with regard to survival. An alternative strategy using FEV(1)/ht(2) 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.