Usual Clinical Parameters Underestimate the Incidence and Significance of Erythropoietin Deficiency as a Risk Factor for Death in Sickle Cell Disease.

A robust reticulocytosis is necessary to maintain hemoglobin levels compatible with life in patients with sickle cell disease. Relative reticulocytopenia, defined as a absolute reticulocyte count less than 250 x 109/L despite hemoglobin <9g/dl, has been identified as a risk factor for early death. RR could result from chronic bone marrow vaso-occlusive insult or a renal endocrine defect leading to erythropoietin (EPO) deficiency. In non-SCD patients, EPO levels and creatinine clearance are clinical parameters that are used to define patients with anemia from EPO deficiency. The normal ranges for these parameters may not apply to SCD, and therefore the incidence and significance of EPO deficiency in SCD may have been underestimated, compromising rational EPO replacement therapy. In a retrospective analysis of 417 patients with HbSS or S-β-thalassemia, confirming previous findings, RR was a risk factor for early death. There was a significant association between RR and proteinuria. Usually, there is an inverse correlation between hemoglobin and EPO levels (negative feed-back), this was seen in patients without RR. However, in patients with proteinuria, the correlation between hemoglobin and EPO levels was a positive one, suggesting hemoglobin dependence on EPO levels. Proteinuria or increased creatinine levels were a risk factor for early death but not if RR was included in the model, suggesting the increased risk of death associated with proteinuria and creatinine was mediated by RR. RR was also associated with decreased platelet and WBC counts, suggesting a contribution by cumulative vaso-occlusive bone marrow damage to RR. However, platelet and WBC counts were not risk factors for early death within the cohort. Damage to renal endocrine function/EPO deficiency should be added to the list of clinically significant chronic organ damage in SCD. EPO deficiency may precede and be causative of other end-organ damage, such as cardiac diastolic dysfunction and renal exocrine failure. Proteinuria should be recognized as a clinical parameter that should prompt consideration of EPO deficiency. Since EPO replacement is clinically feasible, renal endocrine dysfunctiton is a cause of symptoms, clinical deterioration and death that could be rationally addressed.