Serum Transferrin: An Independent Predictor of Mortality in Sickle Cell Anemia

Serum ferritin (SF), the most convenient marker of iron burden in sickle cell anemia (SCA), is potentially confounded by effects of inflammation in SCA. Serum transferrin (STF) has been described as one of the independent predictors of elevated tricuspid regurgitant velocity (TRV) in SCA. Therefore in this report we investigate the potential predictive role of STF in morbidity and mortality of individuals with SCA.

Patients with sickle cell disease documented by high-pressure liquid chromatography were eligible for the study. Four hundred and sixty SCA patients were recruited in this study from the community through multimedia advertisements, community outreach, and regional clinics. All evaluated patients were screened by history taking, physical examination, laboratory studies, and transthoracic echocardiography. All patients provided written informed consent. The advertisements and protocol were approved by the institutional review boards of the National Heart, Lung, and Blood Institute and Howard University. Only outpatients in stable condition were included; patients who had had a vaso-occlusive crisis within the previous two weeks or an episode of acute chest syndrome within the previous four weeks were excluded.

Two hundred and sixty two participants with HbSS were included in the data analysis. Forty-seven percent were male. Median age was 32 years old. Median TRV in this cohort was 2.4 m/s. Forty nine percent of participants had TRV≥2.5 m/s and 19% had TRV≥3 m/s. Patients with lower STF (<164 mg/dl) were older (p=0.01), had more blood transfusions in the past (p<0.0001) and did not have more complications of sickle disease (priapism, acute chest syndrome, leg ulcers or emergency room visits, all p>0.05), but all-cause death rate was higher (22% vs. 6%, p=0.0001). Hemoglobin, CRP, alkaline phosphatase, uric acid, placenta growth factor (<0.001), SF and iron saturation were found to be higher and kidney function was worse. Patients with lower STF level were also more likely to have TRV≥3.0 m/s (32% vs. 13%, p<0. 001) but there was no significant difference in BNP and ejection fraction. Patients with lower STF had endothelial dysfunction, as indicated by a blunted forearm blood flow (FBF) response to infusion of acetylcholine into the brachial artery (p<0.01).

Among age, gender, BNP, TRV,GFR,WBC, STF, systolic blood pressure and fetal hemoglobin, the Cox proportional analysis of mortality found TRV, GFR and STF the independent significant predictors of mortality in this cohort. Kaplan-Meier survival curve showed that patients with transferrin <164 mg/dl had significantly lower survival (p<0.001).

In this cohort of adults with sickle cells anemia, STF is found to be an independent predictor of endothelial dysfunction, high TRV and mortality. It may be a more sensitive predictor than serum ferritin. We propose that iron overload may induce a state of endothelial dysfunction that is a risk factor for clinical vasculopathy and death.

No relevant conflicts of interest to declare.