Staging the severity of chronic obstructive pulmonary disease in older persons based on spirometric Z-scores

Abstract

Objectives: Among older persons, the use of spirometric Z-scores as calculated by the Lambda-Mu-Sigma (LMS) method has a strong scientific rationale for establishing a diagnosis of chronic obstructive pulmonary disease (COPD), but its clinical validity in staging COPD severity is not yet known. The current study has therefore evaluated the association between LMS-staged COPD and health outcomes, in two separate cohorts of older persons.

Design: Longitudinal cohort study.

Setting: The Cardiovascular Health Study (CHS, N = 3,248) and the Third National Health and Nutrition Examination Survey (NHANES-III, N = 1,354).

Participants: Community-living white participants aged 65 to 80.

Measurements: Using spirometric data, COPD was staged as mild, moderate, or severe based on LMS-derived Z-scores. Clinical validity was then evaluated according to all-cause mortality, respiratory symptoms (chronic bronchitis, dyspnea, or wheezing), and moderate to severe dyspnea (available in CHS only).

Results: In CHS, the LMS staging of COPD as mild, moderate, and severe was associated with mortality (adjusted HR (aHR) = 1.50, 95% confidence interval (CI) = 1.15-1.94; aHR = 1.31, 95% CI = 1.03-1.67; and aHR = 2.00, 95% CI = 1.70-2.36, respectively) and with respiratory symptoms (adjusted OR (aOR) = 1.69, 95% CI = 1.12-2.56; aOR = 1.87, 95% CI = 1.28-2.73; and aOR = 3.99, 95% CI = 2.91-5.48, respectively). Also in CHS, moderate and severe, but not mild, LMS-staged COPD was associated with moderate to severe dyspnea (aOR = 2.16, 95% CI = 1.24-3.75; aOR = 3.98, 95% CI = 2.77-5.74; and aOR = 0.84, 95% CI = 0.35-2.01, respectively). Similar associations were found for mortality and respiratory symptoms in NHANES-III, except mild severity was not associated with mortality (aHR = 0.93, 95% CI = 0.62-1.40).

Conclusion: In white older persons, the spirometric staging of COPD severity based on LMS-derived Z-scores was associated with several clinically relevant health outcomes. These results support the use of the LMS method for staging the severity of COPD in older populations.