Modulating factors in the hematopoietic response to erythropoietin.

The absence of any response to the administration of recombinant human erythropoietin (rHuEpo) is exceptional in uremic patients with anemia. Initial "nonresponders" generally respond to higher doses of the hormone. However, a small number of patients may remain unresponsive. The most common cause of limited response is mild to moderate iron deficiency, either at the start of treatment or secondary to enhanced iron utilization by newly formed erythrocytes. Another common cause of resistance is the presence of an overt or, more often, an unrecognized inflammatory state, including acute or chronic infection. Marked aluminum overload and severe hyperparathyroidism also have been shown to induce resistance in at least some patients. Other factors may contribute to the severity of anemia and hence increase rHuEpo requirements, such as acute or chronic hemolytic conditions or blood loss, folate deficiency, hemoglobinopathies, and still poorly defined uremic toxins. In patients who show a resistance to the effect of the recombinant hormone, these should be sought and eliminated, if possible.