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

Abstract

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. Longitudinal cohort study. The Cardiovascular Health Study (CHS, N=3,248) and the Third National Health and Nutrition Examination Survey (NHANES-III, N=1,354). Community-living white participants aged 65 to 80. 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). 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). 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.