Risk of red cell exposure to the water anomaly upon blood unit cold‐storage (2018)

Under the current regulations, blood units, processed as packed red blood cells (PRBC), are stored in the cold room, where the temperature should be kept between 2°C and 6°C, presumably to minimize the chances of contamination and the storage-induced cell lesion. However, noting the water anomaly, we have questioned whether this temperature range indeed provides the optimal conditions for minimizing storage lesion. Differing from other fluids, water is at its' most compact packing at 4°C, below which it undergoes numerous abnormal structural processes, among them the breakage of hydrogen bonds, which affects the water structure and interactions with neighboring molecules. Concomitantly, the water density reaches a maximal value at 4°C, implying that during the routine cold storage PRBC are subjected to repeated temperature fluctuations below and above the 4°C critical temperature, and the respective volume/density variations. As these anomalies are expected to induce instability of membrane-associated water1, 2 and cytoskeleton organization,3 we hypothesized that the current routine cold storage impairs the cell function. RBC are characterized by their deformability, that is, the cells' ability to change their shape under flow-induced shear stress. This is essential for adequate flow, especially in the microcirculation,4 and plays an important role in splenic RBC sequestration. In addition to its own physiological role, RBC deformability can be used for general characterization of the RBC state,5 as it is an integrated characteristic of the cell's features. In recent studies, we have demonstrated that the deformability of transfused PRBC plays a key role in transfusion outcome, as expressed by the transfusion-induced change in the recipients' hemoglobin level6 and blood flow4; both improved with increasing PRBC deformability. On these grounds, we used the PRBC deformability to test the hypothesis that the current routine of storing PRBC at 2°C-6°C is not optimal. It has been previously shown, by us,4, 6 that the routine storage of blood units at 2°C-6°C is associated with a reduction of RBC deformability, which becomes significant around 3 weeks of storage. In accordance with that, in the present study, the deformability of group-1 PRBC (stored at 2.5°C-5.5°C) decreased considerably from day 1 to day 35, whereas the change in the deformability of group-2 PRBC (stored at 5°C-6°C) was insignificant (Table 1). As noted above, of particular relevance to transfusion outcome is the fraction of the low deformable cell in the transfused PRBC population, as this fraction was found in our previous study to inversely correlate with the transfusion-induced increment of the recipients' hemoglobin.6 Table 1 shows that during 35 days of storage, the %LDFC in group-1 increased considerably (from 36.6% to 50.8%, P = 0.0022), while in group 2 PRBC it remained unchanged (36.6%-39.3%, P = 0.2). The effect of storage temperature is especially well demonstrated when comparing the deformability of the individual PRBC units in the two groups. As shown in Supporting Information Figure S1A, for each unit the RBC deformability, expressed by MER (Supporting Information Figure S1A), was higher when stored under 5°C-6°C (group-2) than under the current routine conditions (2.5°C-5.5°C, group-1). This is further demonstrated in Supporting Information Figure S1B, showing that for each PRBC unit the %LDFC in the PRBC population was lower when stored under 5°C-6°C than under 2.5°C-5.5°C. This study shows that storing PRBC under conditions that expose them to the temperature fluctuation around 4°C (group-1), induces a considerable decrease in the RBC deformability, whereas when the exposure to these conditions are avoided (group-2), the RBC deformability is unchanged during storage. As noted above, RBC deformability is an integrative property, and its impairment expresses, in particular, changes in the cell membrane and cytoskeleton structure. Therefore, the finding that storage under group-2 conditions (5°C-6°C) is not associated with damage to RBC deformability may imply that the storage-induced lesion would be smaller when the PRBC are spared from the temperature fluctuations below and above 4°C. The current conventional storage duration has been determined according to the Food and Drug Administration (FDA) requirement for 75% survival of transfused PRBC in the recipient's blood 24 h posttransfusion. On these grounds, the storage-induced change in the percent of a low-deformable cell (%LDFC, see details in Supporting Information), which was considerable in group-1 but insignificant in group-2, is of particular interest. Previous studies have suggested that RBC with low deformability are prone to accelerated clearance from the vascular system.6 In accordance with that, we have found that the fraction of the relatively rigid RBC, as expressed by %LDFC, in the population of transfused PRBC, inversely correlates with the Hb increment in the recipients' blood, measured right after completion of the transfusion. This implies that this measure reflects the survival of transfused PRBC in the recipients' vascular system. Therefore, the fact that the portion of the relatively rigid RBC in group-2 is unchanged during storage may suggest that storing PRBC under conditions that avoid temperature fluctuations below/above 4°C would increase their survival rate and possibly enable longer storage duration. In conclusion, the present study, although of limited scope, demonstrates that the PRBC “quality”, as expressed by the cell deformability, is maintained better when PRBC are not exposed to repeated temperature fluctuations below/above the 4°C critical temperature, where the cells are subjected to the water anomalies. To substantiate this conclusion, further comprehensive study of this phenomenon is needed, but in this experimental study, it is proposed to review the long-standing storage order that is currently practiced in the blood bank. All authors declare no conflict of interest. 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