Anemia and survival in chronic obstructive pulmonary disease: a dichotomous rather than a continuous predictor

Abstract

Background: Chronic obstructive pulmonary disease (COPD) is a disorder characterized by high mortality. Hemoglobin (Hb) concentration has a prognostic impact on COPD patients receiving long-term oxygen treatment, but its value as an independent predictor of survival among stable COPD outpatients has not been fully clarified by previous studies.

Objectives: To investigate the potential association between anemia and survival in a cohort of stable COPD outpatients.

Methods: A cohort of stable COPD patients, who had had their first spirometry, blood count and serum chemistry profile done between October 1999 and November 2010 were retrospectively analyzed. Patients with heart failure, renal impairment, malignancy, recent hemorrhage and other causes of anemia were excluded. Variables that were found to be univariately associated with survival entered a multivariate stepwise Cox regression analysis model, to allow independent predictors of survival to be identified.

Results: Of 294 patients (67.9 ± 9.8 years old, 64.6% male) 15.6% were anemic (Hb <13 g/dl). The median survival differed significantly between anemic [68.7 (18.1-91.5) months] and nonanemic [79.8 (57.5-98.4) months, p = 0.035] individuals. Independent predictors of mortality in the total population were anemia [hazard ratio (HR) 1.87, 95% confidence interval (CI) 1.06-3.29], age (HR 1.08, 95% CI 1.04-1.12) and forced expiratory volume in 1 s (FEV(1)) % predicted (HR 0.94, 95% CI 0.92-0.97); the Hb concentration was neither univariately nor multivariately associated with mortality.

Conclusion: This is the first study to indicate that anemia (but not the Hb value) is independently associated with survival in stable COPD outpatients. It would be better to treat this as a categorical variable in future scoring systems.