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

Chest 2024 March 26
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 percent-predicted versus 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) and GLI-Global (race-neutral) equations were used to determine the Forced Expiratory Volume in 1 second percent-predicted and z-score values. Patients were classified as mild, moderate, or severe according to percent-predicted or z-score thresholds. Association 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 (69.3%) were White (mean age: 65.7 years) and 4,092 (30.7%) Black (mean age: 61.1 years). More Black than White patients had a change in severity classification between approaches when using percent-predicted thresholds (20.2% vs 6.1%, p<0.001) but not with z-score thresholds (12.6% vs 12.3%, p=0.68). An increased severity classification under 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 percent-predicted thresholds (OR 1.08, 95% CI 0.61-1.93). A decreased severity classification under race-neutral was associated with lower risk of exacerbation with both percent-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.

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