Biochemical storage lesions occurring in nonirradiated and irradiated red blood cells: a brief review

Red blood cells undergo a series of biochemical fluctuations during 35-42-day storage period at 1°C to 6°C. The sodium/potassium pump is immobilised causing a decrease in intracellular potassium with an increase in cytoplasmic sodium levels, glucose levels decline, and acidosis occurs as a result of low pH levels. The frailty of stored erythrocytes triggers the formation of haemoglobin-containing microparticles and the release of cell-free haemoglobin which may add to transfusion difficulties. Lipid peroxidation, oxidative stress to band 3 structures, and other morphological and structural molecular changes also occur leading to spheroechinocytes and osmotic fragility. These changes that transpire in the red cells during the storage period are referred to as "storage lesions." It is well documented that gamma irradiation exacerbates storage lesions and the reports of increased potassium levels leading to adverse reactions observed in neonates and infants have been of particular concern. There are, however, remarkably few systematic studies comparing the in vitro storage lesions of irradiated and nonirradiated red cell concentrates and it has been suggested that the impact of storage lesions on leucocyte reduced red blood cell concentrate (RBCC) is incomplete. The review examines storage lesions in red blood cells and their adverse effects in reference to blood transfusion.

Adverse blood transfusion outcomes: establishing causation

The transfusion of allogeneic red blood cells (RBCs) and other blood components is ingrained in modern medical practice. The rationale for administering transfusions is based on key assumptions that efficacy is established and risks are acceptable and minimized. Despite the cliché that, "the blood supply is safer than ever," data about risks and lack of efficacy of RBC transfusions in several clinical settings have steadily accumulated. Frequentist statisticians and clinicians demand evidence from randomized clinical trials (RCTs); however, causation for the recognized serious hazards of allogeneic transfusion has never been established in this manner. On the other hand, the preponderance of evidence implicating RBC transfusions in adverse clinical outcomes related to immunomodulation and the storage lesion comes from observational studies, and a broad and critical analysis to evaluate causation is overdue. It is suggested in several circumstances that this cannot wait for the design, execution, and conduct of rigorous RCTs. We begin by examining the nature and definition of causation with relevant examples from transfusion medicine. Deductive deterministic methods may be applied to most of the well-accepted and understood serious hazards of transfusion, with modified Koch's postulates being fulfilled in most circumstances. On the other hand, when several possible interacting risk factors exist and RBC transfusions are associated with adverse clinical outcomes, establishing causation requires inferential probabilistic methodology. In the latter circumstances, the case for RBC transfusions being causal for adverse clinical outcomes can be strengthened by applying modified Bradford Hill criteria to the plethora of existing observational studies. This being the case, a greater precautionary approach to RBC transfusion is necessary and equipoise that justifying RCTs may become problematic.

Biopreservation of red blood cells--the struggle with hemoglobin oxidation

One of the least recognized causes of cellular damage during ex vivo preservation of red blood cells is oxidative injury to the hemoglobin. The latter has been associated with hemolysis through the release of toxic substances and oxidation of vital cell components. This review delineates some of the major pathways that link hemoglobin oxidation and cellular damage, and summarizes the incidence of red blood cell oxidative injury during hypothermic storage, cryopreservation and desiccation stress. Red blood cell hypothermic storage, despite its success, is not exempt from oxidative injury. Growing evidence portrays a time-dependant oxidative assault including formation of reactive oxygen species, attachment of denatured hemoglobin to membrane phospholipids and the release of hemoglobin-containing membrane microvesicles throughout storage. Similar symptoms have been observed in attempts to stabilize red blood cells in the dried state, in which methemoglobin levels of reconstituted red blood cells reached 50%. Factors affecting the rate of hemoglobin oxidation during red blood cell ex vivo storage include compromised antioxidant activity, high concentrations of glucose in the storage media and the presence of molecular oxygen. Hemoglobin oxidation largely dictates our ability to effectively preserve red blood cells. Understanding its origins along with investigating methods to minimize it can significantly improve the quality of our future blood products.