Transfusions of Red Blood Cells Stored for 40–42 Days Induce Circulating Non-Transferrin-Bound Iron (NTBI) In Healthy Adults

To compare the effects on iron metabolism of transfusion of packed red blood cells (RBCs) after prolonged (40-42 days) and short-term (3–7 days) storage, we prospectively studied 9 healthy adults. Each volunteer donated a standard, leukoreduced, double RBC unit by automated apheresis and was then transfused with the first autologous RBC unit after 3–7 days of storage and the second after 40–42 days of storage. Timed blood samples were obtained just before each transfusion and immediately, 1, 2, 4, 24, and 72-hours after transfusion. Plasma non-transferrin bound iron (NTBI) was quantified by an ultrafiltration assay, serum hepcidin determined by an immunoassay, and complete blood counts and other laboratory measures obtained by standard methods. For each analyte, differences after transfusion of the older and fresher RBCs were evaluated by 2-way ANOVA with a Bonferroni post-test. At 24 hours after transfusion, similar increases in mean hemoglobin concentration were found with the older (0.83 ± 0.54 (SD) g/dL) and fresher (0.74 ± 0.58 (SD) g/dL) units (p=0.30). At 4 hours after transfusion of older RBCs there was a significant, ~3-fold increase over baseline in mean serum iron (by 160 ± 99 mcg/dL with older vs. −7 ± 25 mcg/dL with fresher RBCs, p<0.001), along with ~2-fold rise in mean total serum bilirubin (by 0.52 ± 0.37 mg/dL with older vs. −0.09 ± 0.18 mg/dL with fresher RBCs, p<0.001). There were no significant differences in circulating lactate dehydrogenase or haptoglobin at any time. The significant increases in mean transferrin saturation (p<0.001) and mean change in plasma NTBI (p<0.001) seen after transfusions of older RBCs are shown in the accompanying Figure.

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After transfusion of fresher and older blood, mean serum hepcidin concentrations were not significantly different at any time and no significant differences were found in mean serum C-reactive protein (CRP) or interleukin (IL)-6 levels. Current FDA standards allow refrigerated RBC units to be stored for up to 42 days before transfusion based on the criteria that, on average, less than 25% of the transfused RBCs will be cleared from the circulation in the first 24 hours. In critically ill patients, observational studies identified increases in serious infections, multi-organ failure, and mortality associated with transfusion of older stored RBCs, but the underlying mechanisms have yet to be determined. In healthy volunteers, our results indicate that transfusions of RBCs stored for 3–7 days did not significantly increase serum iron or induce the appearance of plasma NTBI. In contrast, transfusion of RBCs stored for 40–42 days significantly increased serum iron and transferrin saturation and produced substantial amounts of plasma NTBI, in association with the apparently extravascular clearance of a subpopulation of the transfused RBCs. Plasma NTBI can promote bacterial growth and induce oxidative injury. The observed increases in plasma NTBI in healthy volunteers after transfusion of older stored RBCs produced no clinically-evident adverse effects. Nonetheless, in critically ill patients, increases in plasma NTBI may enhance the risk of sepsis, multi-organ failure, and death.

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