• William Checkley, Marilyn G Foreman, Surya P Bhatt, Mark T Dransfield, MeiLan Han, Nicola A Hanania, Nadia N Hansel, Elizabeth A Regan, Robert A Wise, and COPDGene Study Investigators.
• Division of Pulmonary and Critical Care, School of Medicine, Johns Hopkins University, Baltimore, USA; Program in Global Disease Epidemiology and Control, Department of International Health, Bloomberg School of Public Health, Johns Hopkins University, Baltimore, USA. Electronic address: wcheckl1@jhmi.edu.
• Respir Med. 2016 Feb 1; 111: 30-8.

AbstractThe Global Initiative for Chronic Obstructive Lung Disease (GOLD) severity criterion for COPD is used widely in clinical and research settings; however, it requires the use of ethnic- or population-specific reference equations. We propose two alternative severity criteria based on absolute post-bronchodilator FEV1 values (FEV1 and FEV1/height2) that do not depend on reference equations. We compared the accuracy of these classification schemasto those based on % predicted values (GOLD criterion) and Z-scores of post-bronchodilator FEV1 to predict COPD-related functional outcomes or percent emphysema by computerized tomography of the lung. We tested the predictive accuracy of all severity criteria for the 6-minute walk distance (6MWD), St. George's Respiratory Questionnaire (SGRQ), 36-item Short-Form Health Survey physical health component score (SF-36) and the MMRC Dyspnea Score. We used 10-fold cross-validation to estimate average prediction errors and Bonferroni-adjusted t-tests to compare average prediction errors across classification criteria. We analyzed data of 3772 participants with COPD (average age 63 years, 54% male). Severity criteria based on absolute post-bronchodilator FEV1 or FEV1/height2 yielded similar prediction errors for 6MWD, SGRQ, SF-36 physical health component score, and the MMRC Dyspnea Score when compared to the GOLD criterion (all p > 0.34); and, had similar predictive accuracy when compared with the Z-scores criterion, with the exception for 6MWD where post-bronchodilator FEV1 appeared to perform slightly better than Z-scores (p = 0.01). Subgroup analyses did not identify differences across severity criteria by race, sex, or age between absolute values and the GOLD criterion or one based on Z-scores. Severity criteria for COPD based on absolute values of post-bronchodilator FEV1 performed equally as well as did criteria based on predicted values when benchmarked against COPD-related functional and structural outcomes, are simple to use, and may provide a more accessible and comparable approach to severity classification worldwide, especially in settings where prediction equations are not available.Copyright © 2015 Elsevier Ltd. All rights reserved.

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