Comparison of different staging methods for COPD in predicting outcomes

Chronic obstructive pulmonary disease (COPD) is commonly staged according to the percentage of predicted forced expiratory volume in 1 s (FEV1 % pred), but other methods have been proposed. In this study we compared the performance of seven staging methods in predicting outcomes. We retrospectively studied 296 COPD outpatients. For each patient the disease severity was staged by separately applying the following methods: the criteria proposed by the Global Initiative for Chronic Obstructive Lung Disease (GOLD), quartiles of FEV1 % pred and z-score of FEV1, quartiles and specified cut-off points of the ratio of FEV1 over height squared ((FEV1·Ht^-2)A and (FEV1·Ht^-2)B, respectively), and quartiles of the ratio of FEV1 over height cubed (FEV1·Ht-3) and of FEV1 quotient (FEV1Q). We evaluated the performance of these methods in predicting the risks of severe acute exacerbation and all-cause mortality. Overall, staging based on the reference-independent FEV1Q performed best in predicting the risks of severe acute exacerbation (including frequent exacerbation) and mortality, followed by (FEV1·Ht^-2)B. The performance of staging methods could also be influenced by the choice of cut-off values. Future work using large and ethnically diverse populations to refine and validate the cut-off values would enhance the prediction of outcomes.