Determinants of Erythropoietin Level in Steady-state Homozygous Sickle cell Anemia

Abstract

NMJ 2017 Abstract: Background: Previous studies have suggested that erythropoietin (EPO) levels may be inappropriately low in patients with sickle cell disease compared to the extent of the related anemia they demonstrate. Here, we evaluate EPO level vs. renal function, Hb F, and markers of hemolysis for patients with sickle cell disease. Materials and Method: Blood was drawn from 33 patients with hemoglobin SS aged 5-42 years, during routine visits to the outpatient hematology unit in Military Hospital. Hb F, complete blood count, Erythropoietin level and renal function were measured. The data were analyzed using SPSS 19 and Pearson correlation test was used to find correlation. P value < 0.05 was considered significant. Results: Neither age nor gender have an effect on EPO level. In addition, a correlation between Hb level and EPO was not consistently observed. Higher EPO levels were seen in patients with high HbS percentage, but no correlation with hemolysis, renal function, or inflammation was observed. Conclusion: Erythropoietin levels in patients with sickle cell disease do not correlate with known inducers of erythropoietin in healthy individuals. Introduction: Homozygous sickle cell Anaemia(SCA) is an autosomal recessive genetic disease that results from the substitution of valine for glutamic acid at position 6 of the β-globin chain, leading to production of haemoglobin S (HbS)(1). Erythropoietin (EPO) is the hematopoietic cytokine that regulates red blood cell production (2).It is produced by peritubular interstitial cells in the renal cortex in response to hypoxia(3). Serum EPO levels are often elevated in chronic anemic states like SCD (4). Though other studies reveled sickled patients produce less EPO at a given hemoglobin concentration than do patients with nonhemoglobinopathy anemia(5-7).This can be explained since sickle hemoglobin has a ‘right-shifted oxygen dissociation curve (lower affinity), in which HbS releases more oxygen to tissues at any given oxygen tension than HbA does. Thus, the hypoxia-driven erythropoietin response to anemia may be blunted in steady state SCD (4;8;9). Therefore, relative EPO deficiency could be a contributing factor to the anemia observed in SCA patients(9). The erythropoietin response in several anemias has been linked to hemoglobin level and tissue hypoxia(10). Though EPOlevel stimulating factors are not easily understood in SCDpatients (11). Since increased red cell production is necessary to maintain given hemoglobinlevel in patients with a hemolytic disorder like SCD, but it alters EPO/hemoglobin correlations (11). Erythroid hyperplasia may involve a faster clearance of EPO (12). Other factor that complicates EPO response in SCD is the presence of renal damage that is sufficient to decrease renal endocrine function without affecting serum urea and creatinine level (11). NMJ April 2017 vol.5 No.20 ISSN 1858-6155 76 NMJ 2017 In this study we Here, we evaluate EPO level vs. renal function, HbF level, hemolysis markers and markers of inflammation for patients treated for sickle cell disease. Materials and Methods: This was descriptive cross sectional study, conducted from June to November 2014. Blood was drawn from 33 patients with sickle cell anemia during routine visits to the outpatient hematology units, Military hospital- Khartoum-Sudan. Inclusion criteria were: patients homozygous for SCD (SS) as documented by Hemoglobin electrophoreses, aged between 5 and 50 years. Exclusion criteria: patients received blood transfusion within the last three months or admitted to the hospital within 2 weeks because of SCD-related events or crisis. The total number of participants recruited mounted to 33. Five milliliter (ml) of venous blood was collected from each patient, 2.5 ml in(EDTA) container for hematological investigations, measure Hb F level and estimation of plasmaEPO level, and 2.5 ml in lithiumheparin containerfor estimation of LDH. Blood cell counts were performed using automated hematology analyzer "Sysmex”. Hemoglobin F was measured by modified fully automated capillary2 flexpiercing hemoglobin electrophoresis technique (Sepia France). LDH was measured by automated chemistry analyzer "Cobas, Integera 400 plus. Plasma was separated from EDTAsample and used for estimation of EPO level by enzyme-linked immunosorbent assay (ELISA) using "Wkea, USA" EPOELISA kit. An ethical clearance was obtained from the Institutional Review Board at Alneelain University. Principal investigator obtained written informed consent from each participant or from parents when the patient was less than 18 years old. The data were analyzed using SPSS 19 and Pearson correlation test was used to find correlation. P value < 0.05 was considered significant. Results: Thirty three patients with HbSS were enrolled in this study 19 (57.6%) of them were males and 14(42.4%) were females; age ranged between 5 and 42years (mean ±SD: 16.12±8.9years). Five patients were on a stable dose of hydroxylurea (500mg/day). Erythropoietin level and hematological values are represented in table 1. Gender has no effect on EPO level (P value: 0.972). Age also showed no significant correlation with EPO level (Pearson correlation:-0.22, P.value:0.91). Table 2 indicates the correlations between fetal hemoglobin (HbF), sickle hemoglobin (HbS), hemoglobin, WBCs count, total bilirubin, LDH and EPO level. And correlation was only significant between EPO and HbF and HbS. Linear regression model is illustrated in figure I& II. There was no significant