The discovery in the 1915 of sodium citrate as blood anticoagulant (1) has started the possibility to store the blood in blood banks. Further introduction of modern preservation solutions as for example CPDA (citrate-phosphate-dextrose-adenine) or CPD+SAGM (saline-adenine-glucose-mannitol) used in Europe, prolonged the time of red blood cells (RBCs) storage to 42 days. The primary goal of every blood bank is to prepare RBCs being able to efficiently deliver oxygen to the tissue and survive in the recipient circulation long enough to perform its functions. The collection, processing, testing, production and storage procedures in blood banks are closely regulated by special directives and guidelines (2, 3). Until now many biochemical processes of RBCs have been well described. More and more is known about the functions of individual molecules of erythrocyte membrane. But still little understood is the total protein composition of erythrocytes, nor the changes that RBC undergo during 120 days of their life, in conditions of many hematological disorders and during storage under blood bank conditions.

During storage RBCs undergo a number of biochemical, morphological and metabolic changes known as “storage lesions”. For example, it is well described, that due to the accumulation of lactic acid in the blood bag, the pH decreases, and this increases phosphatase 3 enzyme activity, which results in 2,3-diphosphoglycerol (2,3-DPG) degradation. Low level of 2,3-DPG results in increased oxygen affinity to hemoglobin, and thereby causes diminished delivery of oxygen to tissues (4). During RBCs storage period there appear also changes in ATP level what can reflect on reology of erythrocyte (5), loss of S-nitrosothiol-haemoglobin (SNO-Hb) – and thereby decreased NO production and further vasodilatation, as well as membranous band 3 protein and some other proteins rearrangements (6). RBCs display unique reological possibilities provided, among other, by the sophisticated interactions of membrane and cytoskeletal proteins. This enables passage of RBCs through the blood vessels, which are often narrower than erythrocytes. Reduced flexibility will result in impaired perfusion and oxygen delivery to peripheral tissues; moreover, rigid RBCs might directly block capillaries. There are evidences from the in vitro analysis that RBCs storage induces a broad range of impairments of RBC hemodynamic behavior such as deformability, aggregability, and adherence to endothelial cells (7). It was also reported that serious hemorheological disorders, including the decrease in RBC deformability secondary to shape abnormalities, acidosis, and the decrease of blood clotting, start already at the second week of storage and progress up to the end of the storage period (8). There are also evidences of leukocyte influence on increase of RBCs adherence to the endothelial cell layer (9). In the membrane are localized inhibitors of complement pathway, protecting from haemolysis (10) and also proteins taking part in clotting process, transporters, receptors, adhesion molecules and molecules carrying RBC antigens (11).

Red blood cells are the most commonly transfused blood component. Some of the “storage lesions” mentioned above lead to removal of erythrocytes from the circulation but still a huge percentage of RBCs is recovered after transfusion and it is assessed that around 70-75% of them are present in the circulation after 24 hours post transfusion (12).

For twenty years now, there is alive debate concerning the functionality of fresh, several days stored, versus old – 14, 21, 28 or 35 ≥ days long stored blood, as well as leucoreduced versus non-leucoreduced RBCs. Opinion that the functionality of transfused blood from different storage periods can not be regarded as a comparable is supported by many clinicians, mainly from cardiology units who pay attention on different recoveries depending on the storage period and presence of leukocytes in the blood the patient received. These concerns mostly patients with acute coronary syndrome, ischemic heart disease or after coronary interventions, who are particularly susceptible to effects of hypoxia, activation of thrombosis, effects of heamolysis. Many authors demonstrated an increased in-hospital and out-of-hospital mortality among hospitalized patients associated with increased mean age of RBCs transfused (13, 14). Study of patients who were undergoing coronary-artery bypass grafting, cardiac-valve surgery, revealed that transfusion of RBCs stored for more than 2 weeks was associated with a significantly increased risk of postoperative complications. In-hospital death, prolonged intubation, renal failure, septicemia or sepsis, multiorgan failure, and a composite of serious complications were all more frequent in patients given blood stored for more than 14 days. Furthermore, survival, particularly in the first 6 months after surgery, was significantly reduced (15).

However, one should also take into account the possibility that there is no problem with the storage of RBCs, but rather an incorrect analysis of the cases examined (16).