Association between hemoglobin and prognosis in patients admitted to hospital for COPD
Low concentrations of hemoglobin have previously been demonstrated in many patients with COPD. There is evidence of anemia as a prognostic factor in acute exacerbations, but the detailed relationship between concentrations of hemoglobin and mortality is not known. A register-based cohort of patients admitted for the first time to Danish hospitals for acute exacerbations of COPD from 2007 through 2012 was established. Age, sex, comorbidities, medication, renal function, and concentrations of hemoglobin were retrieved. Sex-specific survival analyses were fitted for different rounded concentrations of hemoglobin. The cohort encompassed 6,969 patients. Hemoglobin below 130 g/L was present in 39% of males and below 120 g/L in 24% of females. The in-hospital mortality rates for patients with hemoglobin below or above these limits were 11.6% and 5.4%, respectively. After discharge, compared to hemoglobin 130 g/L, the hazard ratio (HR) for males with hemoglobin 120 g/L was 1.45 (95% confidence interval [CI] 1.22-1.73), adjusted HR 1.37 (95% CI 1.15-1.64). Compared to hemoglobin 120 g/L, the HR for females with hemoglobin 110 g/L was 1.4 (95% CI 1.17-1.68), adjusted HR 1.28 (95% CI 1.06-1.53). In conclusion, low concentrations of hemoglobin are frequent in COPD patients with acute exacerbations, and predict long-term mortality.