Changes in Spirometry Interpretative Strategies: Implications for Classifying COPD and Predicting Exacerbations

J Henry Brems; Aparna Balasubramanian; Sarath Raju; Nirupama Putcha; Ashraf Fawzy; Nadia N Hansel; Robert A Wise; Meredith C McCormack

doi:10.1016/j.chest.2024.03.034

Changes in Spirometry Interpretative Strategies: Implications for Classifying COPD and Predicting Exacerbations

Chest. 2024 Mar 26:S0012-3692(24)00423-9. doi: 10.1016/j.chest.2024.03.034. Online ahead of print.

Authors

J Henry Brems¹, Aparna Balasubramanian², Sarath Raju², Nirupama Putcha², Ashraf Fawzy², Nadia N Hansel², Robert A Wise², Meredith C McCormack²

Affiliations

¹ Division of Pulmonary and Critical Care Medicine, Johns Hopkins University, Baltimore, MD; Berman Institute of Bioethics (J. H. B.), Johns Hopkins University, Baltimore, MD. Electronic address: jbrems2@jh.edu.
² Division of Pulmonary and Critical Care Medicine, Johns Hopkins University, Baltimore, MD.

PMID: 38537688
DOI: 10.1016/j.chest.2024.03.034

Abstract

Background: Recent guidelines for spirometry interpretation recommend both race-neutral reference equations and use of z score thresholds to define severity of airflow obstruction.

Research question: How does the transition from race-specific to race-neutral equations impact severity classifications for patients with COPD when using % predicted vs z score thresholds, and do changes in severity correspond to clinical risk?

Study design and methods: This retrospective cohort study included Black and White patients with COPD and available spirometry from the Johns Hopkins Health System. Global Lung Function Initiative (GLI) 2012 (race-specific) equations and GLI Global (race-neutral) equations were used to determine FEV₁ % predicted and z score values. Patients were classified as having mild, moderate, or severe disease according to % predicted or z score thresholds. Associations between a change in severity classification from race-specific to race-neutral with COPD exacerbations and all-cause hospitalizations were evaluated using logistic regression.

Results: This cohort included 13,324 patients, of whom 9,232 patients (69.3%) were White (mean age, 65.7 years) and 4,092 patients (30.7%) were Black (mean age, 61.1 years). More Black than White patients showed a change in severity classification between approaches when using % predicted thresholds (20.2% vs 6.1%; P < .001), but not with z score thresholds (12.6% vs 12.3%; P = .68). An increased severity classification with a race-neutral approach was associated with increased risk of exacerbation when using z score thresholds (OR, 2.34; 95% CI, 1.51-3.63), but not when using % predicted thresholds (OR, 1.08; 95% CI, 0.61-1.93). A decreased severity classification with a race-neutral approach was associated with lower risk of exacerbation with both % predicted (OR, 0.49; 95% CI, 0.28-0.87) and z score (OR 0.67; 95% CI, 0.50-0.90) thresholds.

Interpretation: The proportions of Black and White individuals reclassified were similar with z score thresholds, and changes in severity corresponded to clinical risk with z scores. These results support recent recommendations for use of race-neutral equations and z score thresholds for spirometry interpretation.

Keywords: % predicted; COPD; race; reference equations; spirometry; z score.

Abstract

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