Hemoglobin levels above anemia thresholds are maximally predictive for long-term survival in COPD with chronic respiratory failure.

BACKGROUND: In patients with COPD, chronic anemia is known as an unfavorable prognostic factor. Whether the association between hemoglobin (Hb) levels and long-term survival is restricted to anemia or extends to higher Hb levels has not yet been systematically assessed.
METHODS: We determined Hb levels in 309 subjects with COPD and chronic respiratory failure prior to initiation of noninvasive ventilation, accounting for confounders that might affect Hb. Subjects were categorized as anemic (Hb < 12 g/dL in females, Hb < 13 g/dL in males), polycythemic (Hb ≥ 15 g/dL in females, Hb ≥ 17 g/dL in males), or normocythemic. In addition, percentiles of Hb values were analyzed with regard to mortality from any cause.
RESULTS: Two-hundred seven subjects (67.0%) showed normal Hb levels, 46 (14.9%) had anemia, and 56 (18.1%) had polycythemia. Polycythemic subjects showed a higher survival rate than anemic (P = .01) and normocythemic subjects (P = .043). In a univariate Cox hazards model, Hb was associated with long-term survival (hazard ratio 0.855; 95% CI 0.783-0.934, P < .001). The 58th percentiles of Hb (14.3 g/dL in females, 15.1 g/dL in males) yielded the highest discriminative value for predicting survival (hazard ratio 0.463, 95% CI 0.324-0.660, P < .001). In the multivariate analysis this cutoff was an independent predictor for survival (hazard ratio 0.627, 95% CI 0.414-0.949, P = .03), in addition to age and body mass index.
CONCLUSIONS: In subjects with COPD and chronic respiratory failure undergoing treatment with noninvasive ventilation and LTOT, high Hb levels are associated with better long-term survival. The optimal cutoff level for prediction was above the established threshold defining anemia. Thus, predicting survival only on the basis of anemia does not fully utilize the prognostic potential of Hb values in COPD.