EDITORIAL: Red blood cell hemolysis: an old standard in changing times

T he advent of acid-citrate-dextrose (ACD) storage solution effectively initiated 4°C whole blood storage and has provided the basis for many subsequent red blood cell (RBC) storage developments. Since early studies had shown poor RBC preservation in the presence of storage induced hemolysis, these studies included a 1% poststorage hemolysis goal. Later developments focused on the avoidance of the collection lesion and utilized osmotic fragility hemolysis measurements as one of the markers of stored RBC quality in the development of citrate-phosphate-dextrose (CPD). Ensuing developments focused on packed RBCs, which had the limitation that reduced RBC quality was observed if storage hematocrit (Hct) exceeded 70% and was associated with increased poststorage hemolysis. Since these RBC quality deficiencies were noted at the same time as the conversion to CPD-adenine, the newer storage solutions contained higher glucose levels to ensure adequate nutrient availability for satisfactory RBC recoveries at the end of 35 days of storage. At 35 days with a 75% storage Hct, CPDA-1 packed cell supernatant hemoglobin (Hb) levels averaged approximately 0.4% with CPDA-1–packed RBC posttransfusion recovery of 71%, which then supported product approval. The current generation of RBC additive solutions (ASs) was driven by the need to correct the poor CPD flow properties through the addition of saline-adenine-glucose (SAG) solutions. Hemolysis levels averaged 0.77%, although it was noted that posttransfusion recoveries were unaffected. Later it was shown that poststorage hemolysis levels in SAG-RBCs could be reduced by the addition of plasma or by reduction of white cell content. The effect of white blood cells (WBCs) could be reduced by enzyme inhibitors suggesting that it was intracellular enzymes that affected RBC membranes. Subsequent AS development included buffy coat (BC) depletion as a prerequisite, and formulations included mannitol (SAGM), an osmotic stabilizer, since the combination exhibited poststorage hemolysis comparable to whole blood. The concern about hemolysis was a principal goal of AS-1 development. This solution allowed the storage of nonleukoreduced RBCs for 42 days after high-efficiency plasma removal with poststorage hemolysis averaging approximately 0.27% (Adsol, Fenwal, Inc., Lake Zurich, IL). The addition of extra mannitol was essential for reduced hemolysis, since comparable non–mannitol (AS3)-based additives were associated with hemolysis levels averaging 0.7 0.56% compared to mannitol-based additives (0.38 0.19%). The formulation of SAGM adopted for the US market contained a higher adenine load and comparable mannitol levels to that of SAGM but exhibited slightly greater 42-day poststorage hemolysis than AS-1 (AS-5, Optisol, Terumo, Inc., Elkton, MD). Later review of current US AS formulations (AS-1, AS-3, and AS-5) suggested that although RBC viability correlated reasonably with RBC ATP (r = ~0.6) in standard RBC products, hemolysis correlated poorly (r = ~0.4) with viability. It was the later development of high efficiency prestorage 3to 5-log leukoreduction filters that enabled significant reductions in poststorage hemolysis from 0.54% to 0.18%. These studies showed a small (2%-3%) but significant improvement in RBC recoveries and that residual unfiltered WBC content correlated with RBC lactate production; in filtered units glucose consumption correlated with poststorage osmotic fragility, suggesting a membrane-based stress effect on RBC metabolism. RBC recoveries in filtered units correlated with hemolysis after 42 days of storage when the long-term membrane effect might be expected to be at its greatest. Other studies failed to show such a relationship. European-style additives (SAGM) in routine use have therefore included leukoreduction, initially through BC reduction using topand-bottom bags and more recently with the addition of prestorage leukofiltration. In the United States, AS systems are used mostly with prestorage filtration. The Australian family of additives (AS-3) included more adenine and citrate instead of mannitol, modified through the addition of high-efficiency prestorage leukofiltration (Leukotrap-RC system, Pall Corp., Roslyn, NY). In this issue of TRANSFUSION, Hess and the BEST team review the hemolysis quality outcome measures in AS-RBC over approximately 10 years of routine AS RBC manufacture and storage. This study includes a large enough sample size to offer insights into the effect of different solutions and some perspective on biologic variability in practice. These studies confirmed a significant effect of prestorage leukoreduction on poststorage hemolysis. In the largest comparison, the use of highefficiency prestorage leukofiltration reduced hemolysis by approximately 50% from 0.34% in standard units to 0.16%, a reduction similar to that of earlier studies. It should be noted that the BC reduced/unfiltered group utilized AS-1, which contains approximately 1.7 ¥ the amount of adenine of the earlier SAGM, although this fact would be unlikely to explain AS-1 and SAGM differences. TRANSFUSION 2009;49:2551-2554.