Low erythropoietin levels in cystic fibrosis

Polycythemia is the usual compensatory response to chronic tissue hypoxia. Despite tissue hypoxia, patients with cystic fibrosis (CF) are frequently anemic and almost never polycythemic. We measured the blood levels of hemoglobin (Hg) and erythropoietin (EPO) in anemic and nonanemic patients with CF. These levels were then compared to normal and anemic control subjects. The central venous oxygen content (CvO(2)), partial pressure of oxygen (PvO(2)), and percent hemoglobin-oxygen saturation (SvO(2)) were then correlated with EPO levels in anemic patients with and without CF. The EPO levels of patients with CF and anemia were significantly lower than those of control subjects with the same degree of anemia (12.39+/-1.49 versus 60.94+/-23.65; p <0.05) and were not significantly different from those of nonanemic patients with CF and normal subjects. EPO levels in nonanemic patients with CF did not differ from those of normal subjects. The National Institutes of Health (NIH) scores (disease severity) were lower in the anemic CF group than in the nonanemic group of patients with CF. CvO(2), PvO(2), and SvO(2) were significantly lower in the anemic CF group than in the control group with anemia (8.2 versus 10.2 ml/dl, 32 versus 40 mm Hg and 57 versus 71%, p <0.01). EPO levels were lower in the CF group but not significantly; Albumin levels were lower in the anemic CF group than in the control group with anemia (3.12+/-0.09 versus 4.0+/-0.10; p <0.01). Vitamin levels and iron storage were in the normal range or higher in both groups of patients. EPO levels were lower in the anemic CF patients despite the presence of tissue hypoxia. The presence of anemia in some of our CF patients may be related to inadequate EPO production, since iron stores and vitamin levels were adequate for bone marrow production. The low EPO levels could be secondary to malnutrition, since the CF group with anemia had lower albumin levels and lower NIH scores. Our data indicate that when CF becomes more severe, the expected increase in EPO production in response to chronic tissue hypoxia is not sufficient to meet the demands for red cell production.