Sickle Cell Index Monitoring for Autologous Blood Conservation- Exchange Transfusion, Storage and Cell Salvage

Background and objectives: Homozygous sickle cell disease (SCD) patients frequently are alloimmunized resulting in restricted compatible blood supply. Methods to reduce exposure to allogeneic blood are not used frequently. Autologous blood from HbSS patients cannot be used because there is not a safe way to determine if it is suitable for re-transfusion.This feasibility study aims to establish the sickle cell index (SCI) as a monitor for the safe use of HbSS blood from autologous predonation (PAD), storage, and oxygenated cell salvage. Materials and methods: HbSS blood units were stored as whole blood (WB) in CPDA-1 (n=4) or as packed red blood cells (PRBC) in SAG-M (n=4) for 42 days. Following storage at day 42, 3 stored WB and PRBC units were processed by oxygenated cell salvage in buffered washing solution. Quality of HbSS blood was assessed weekly by SCI during storage. Results were compared to HbA data obtained from healthy donor units with respective storage solutions. Results: SCI correlated well with hemoglobin-S-fraction fraction (r=0.9625). During storage in SAG-M, sickling indicated by SCI increased continuously from day 21 on. In contrast, SCI in CPDA-1 units increased from day 1 on. In stored blood units with high SCI levels (>10‰), cell salvage reduced cell sickling and hemolysis. Conclusion: SCI is feasible and useful for monitoring sickling in HbSS blood during exchange transfusion, storage, and cell salvage. As indicated by SCI, sickling of SCD blood in-vitro increased during storage but occurred later in SAG-M as opposed to CPDA-1. Monitoring of SCI revealed that oxygenated and buffered cell salvage improves SCD blood quality. Autologous methods in combination with SCI monitoring therefore may be appropriate to reduce allogeneic blood transfusion in SCD.