Inadequate erythroid response to hypoxia in cystic fibrosis

An increase in hemoglobin concentration characterizes the normal compensatory response to chronic tissue hypoxia. We observed no such increase in 42 chronically hypoxic patients with cystic fibrosis, in whom the mean concentration was 12.6 gm/dl; one third of the patients were anemic. Compared with patients with cyanotic heart disease, patients with cystic fibrosis did not have a compensatory increase in P50 or 2,3-diphosphoglycerate. Despite anemia, erythropoietin levels in patients with cystic fibrosis were not significantly different from normal control values. The growth of colony-forming units-erythroid in patients with cystic fibrosis was similar to that in control subjects, and there was no inhibition of growth with the addition of autologous serum. Erythropoietin sensitivity, determined by measuring the CFUe dose response curve, was normal in both patients and controls. Results of iron studies were consistent with iron deficiency in the majority of patients. Impaired absorption of iron was observed in six of 13 iron-deficient patients with cystic fibrosis. An inverse correlation between erythrocyte sedimentation rate and peak serum iron was obtained during the iron absorption study. Eight patients who underwent a therapeutic trial of iron demonstrated a 1.8 gm/dl rise in hemoglobin concentration. Two patients with previously documented iron malabsorption responded to parenteral iron therapy after failure to respond to oral supplementation. These studies demonstrate that patients with cystic fibrosis not only have an impaired erythroid response to hypoxia, but are frequently anemic. Their inadequate erythroid response to hypoxia results in part from disturbances in erythropoietin regulation and iron availability.