title: Differences between absolute and predicted values of forced expiratory volumes to classify ventilatory impairment in chronic obstructive pulmonary disease.
abstract: The 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.
authors.affiliation: 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.
authors.forename: William
authors.initials: W
authors.lastname: Checkley
authors.affiliation: Division of Pulmonary and Critical Care Medicine, Morehouse School of Medicine, Atlanta, USA.
authors.forename: Marilyn G
authors.initials: MG
authors.lastname: Foreman
authors.affiliation: Division of Pulmonary, Allergy and Critical Care Medicine, School of Medicine, University of Alabama at Birmingham, Birmingham, USA.
authors.forename: Surya P
authors.initials: SP
authors.lastname: Bhatt
authors.affiliation: Division of Pulmonary, Allergy and Critical Care Medicine, School of Medicine, University of Alabama at Birmingham, Birmingham, USA.
authors.forename: Mark T
authors.initials: MT
authors.lastname: Dransfield
authors.affiliation: Division of Pulmonary and Critical Care Medicine, School of Medicine, University of Michigan, Ann Arbor, USA.
authors.forename: MeiLan
authors.initials: M
authors.lastname: Han
authors.affiliation: Section of Pulmonary, Critical Care, and Sleep Medicine, Baylor College of Medicine, Houston, USA.
authors.forename: Nicola A
authors.initials: NA
authors.lastname: Hanania
authors.affiliation: Division of Pulmonary and Critical Care, School of Medicine, Johns Hopkins University, Baltimore, USA.
authors.forename: Nadia N
authors.initials: NN
authors.lastname: Hansel
authors.affiliation: Division of Rheumatology, Department of Medicine, National Jewish Health, Denver, USA.
authors.forename: Elizabeth A
authors.initials: EA
authors.lastname: Regan
authors.affiliation: Division of Pulmonary and Critical Care, School of Medicine, Johns Hopkins University, Baltimore, USA.
authors.forename: Robert A
authors.initials: RA
authors.lastname: Wise
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D005260:Female; D005541:Forced Expiratory Volume; D006801:Humans; D008297:Male; D008875:Middle Aged; D011237:Predictive Value of Tests; D029424:Pulmonary Disease, Chronic Obstructive / Q000175:diagnosis* / Q000000981:diagnostic imaging / Q000235:genetics / Q000503:physiopathology*; D012131:Respiratory Insufficiency / Q000235:genetics / Q000503:physiopathology*; D012720:Severity of Illness Index; D013147:Spirometry / Q000379:methods
keywords: COPD; Reference equations; Severity criteria