Читать книгу Transfusion Medicine - Jeffrey McCullough - Страница 128

RBCs are the cells remaining after most of the plasma has been removed from WB. They must have a final hematocrit of less than 80% [24]. This blood component is often called “packed red cells” or “packed cells.” Usually the red cells and plasma are separated within 8 hours of collection, because for the plasma to be used as a source of factor VIII it must be placed in the freezer less than 8 hours after collection.Centrifugation is used when the red cells are being prepared within a few hours after collection, because usually this is done as part of a large‐scale operation, and speed is important. The centrifugation conditions (time and speed) are determined by the method being used to prepare the platelets or plasma. If platelets or fresh frozen plasma (FFP) are not being produced from the original unit of WB, the red cells can be separated from the plasma at any time during the storage period of the blood. If the unit of WB is allowed to remain undisturbed for several hours, the red cells sediment and the plasma can be removed. When sedimentation is used, the red cells are not as concentrated; as a result, the red cell unit has a lower hematocrit and less plasma is recovered. Because the plasma is valuable as a source for production of plasma derivatives, it is desirable to recover the maximum amount of plasma; therefore, sedimentation currently is not usually used to separate WB into its components. However, sedimentation can be used quite effectively when equipment for centrifugation is not available, such as in developing countries.

The unit of red cells has a volume of about 300 mL and will contain a minimum of 154 mL of red cells (405 mL × 38% hematocrit). Usually the red cell unit contains about 190 mL of red cells (450 mL × 42% hematocrit) and has a hematocrit of about 60%. The fluid portion of the unit (approximately 130 mL) is primarily the additive preservative solution, although about 20 mL of plasma remains from the original unit of WB. The characteristics of a unit of red cells stored in an additive are listed in Table 5.6 and the general changes in Table 5.7. Considerable emphasis has been put to understanding these changes and the potential clinical impact (see Chapters 11 and 16). One unit of red cells will increase the hemoglobin concentration and hematocrit in an average‐size adult (70 kg) by about 1 g/dL and 3%, respectively.

Studies of biochemical and morphologic alterations that occur during storage of RBCs have expanded to investigate not only the correlation between storage lesion and anticoagulant–preservative solutions but also donor‐to‐donor variability. In 2013, RBC‐Omics Recipient Epidemiology Donor Evaluation (REDS)‐III study was lunched [25]. One of the main objectives of the study was to determine whether genetic and biological variability of blood donors defines the quality of RBCs and their capacity to withstand cold storage temperatures. The study demonstrated an association between donor characteristics, such as sex, age, race/ethnicity, iron intake, and donation frequency, and in vitro hemolysis in RBC product [26–28]. A genome‐wide association study provided additional information on gene loci and association with hemolysis [27, 29]. Overall, the new way of thinking about “storage lesion” and RBC‐Omics paves the way for future studies.