A Comparison of Automated Red Blood Cell Depletion/Exchange to Automated Red Cell Blood Exchange in Sickle Cell Patients.

Chronic red blood cell (RBC) exchange transfusion (RBCX) is employed in the prevention and treatment of complications from sickle cell disease (SCD). Although regular automated RBCX by an apheresis device can consistently maintain a low sickle hemoglobin (HbS) percentage at a relatively constant hematocrit level (Hct) with no iron loading, it exposes the patient to significantly more donor erythrocyte units than simple (top-up) transfusion. Since October 2010 the University Health Network, a sickle cell comprehensive care centre in Canada, has started performing automated depletion RBCX with the Caridian Optia Apheresis System. In depletion/exchange, a portion of the patient's RBC is first cytapheresed by the apheresis device prior to the exchange phase of the procedure, with albumin as colloid replacement to maintain intravascular volume and pressure. The clinical effectiveness of depletion/exchange has not been demonstrated in a systematic manner. A retrospective observational cohort study was conducted to investigate the hypothesis that depletion/exchange RBCX, when compared to traditional automated RBCX, will reduce a patient's donor RBC exposure while providing similar hematological and clinical benefit. The laboratory and clinical outcome 1 year before (October 1, 2009) and 1 year after (October 30, 2011) the introduction of depletion/exchange RBCX were compared on a patient-by-patient, rather than on an aggregate, basis.

Seven patients, 2 females, 5 males, median age 29 years (range 26 – 38 years), totaling 135 RBCX sessions were examined. Five patients were homozygous for the sickle mutation and 2 were SC compound heterozygotes (HbSC). Stroke was the most prevalent indication (n = 3). Median interval between exchange sessions was 5 weeks (range 4 – 8 weeks). The fraction cell remaining (FCR) was fixed at 20 and did not change when patients were transitioned from non-depleted to depleted exchange. The minimum Hct was reduced to 0.24 in all patients. The inlet speed of the apheresis device and anticoagulant ratio employed were similar across all patients. There was no significant difference in pre-RBCX HbS (or HbS+C in HbSC patients) in 6 patients (P value ranged from 0.0589 to 0.6870). The pre-RBCX HbS was higher with depletion/exchange in 1 patient (P = 0.0071). There was no significant difference in post-RBCX Hct in 5 patients (P value ranged from 0.1056 to 0.8995), and in 2 patients, the mean post-RBCX Hct was lower with depletion/exchange (P = 0.0004 and 0.0148). The mean RBC volume used was reduced by 25 mL/kg/year with depletion/exchange. The mean volume of albumin used was 6.0 ± 2.5 mL/kg per session. Ferritin remained stable throughout the study period (P = 0.2289). None of the patients were on iron chelators. There was no significant difference in mean duration of RBCX session between depletion/exchange and non-depletion exchange in all patients except one. The median duration of one session was 148 ± 51 min. and 147 ± 43 min. in depletion/exchange and non-depletion exchange respectively. A total of 11 adverse events occurred in 135 sessions, with citrate reaction being the commonest (n = 4). There was no significant difference in the rate of adverse event between depletion and non-depletion RBCX (8/74 and 4/61 respectively, P = 0.3874). There was also no incidence of treatment failure, defined as the occurrence of an SCD-related complication in which the RBCX was intended to prevent, in any of the patients during the entire study period, regardless of RBCX method.

In this first clinical study of depletion/exchange, this strategy significantly reduced RBC usage in majority of the patients without any negative impact on laboratory and clinical outcome. The use of depletion/exchange reduced RBC usage by 25 mL/kg/year, equivalent to 5 units of packed RBC in a 60 kg person. Further optimization of the technique by modification of the FCR and minimum Hct may yield higher reduction in RBC usage, thereby reducing the risk of exposure to blood products.

No relevant conflicts of interest to declare.