Red blood cell transfusions are given to raise the hemoglobin levels in patients with anemia or to replace losses after acute bleeding episodes.
PREPARATIONS OF RED CELLS FOR TRANSFUSION
Several types of preparations containing red blood cells are available (whole blood, packed red blood cells, frozen red blood cells, or autologous non-frozen red blood cells).
The advantage of whole blood for transfusion is the simultaneous presence of red blood cells, plasma, and fresh platelets. Fresh whole blood is not absolutely necessary, since all the above components are available separately. The major indications for use of whole blood are cardiac surgery or massive hemorrhage when more than 10 units of blood is required in a 24-hour period.
B. Packed Red Blood Cells
Packed red cells are the component most commonly used to raise the hemoglobin. Each unit has a volume of about 300 mL, of which approximately 200 mL consists of red blood cells. One unit of packed red cells will usually raise the hemoglobin by approximately 1 g/dL. Current guidelines recommend a transfusion “trigger” hemoglobin threshold of 7–8 g/dL (70–80 g/L) for hospitalized critically ill patients, those undergoing cardiothoracic surgery or repair of a hip fracture, those with upper gastrointestinal bleeding, and those with hematologic malignancy undergoing chemotherapy or hematopoietic cell transplant.
C. Frozen Packed Red Blood Cells
Packed red blood cells can be frozen and stored for up to 10 years, but the technique is cumbersome and expensive and should be used sparingly. The major application is for the purpose of maintaining a supply of rare blood types. Patients with such types may donate units for autologous transfusion should the need arise. Such patients may need a frozen unit preserved from an identically red blood cell phenotyped allogeneic donor for use in emergencies. Frozen red cells are also occasionally needed for patients with severe leukoagglutinin reactions or anaphylactic reactions to plasma proteins, since frozen blood has essentially all white blood cells and plasma components removed.
D. Autologous Packed Red Blood Cells
Patients scheduled for elective surgery may donate blood for autologous transfusion. These units may be stored for up to 35 days before freezing is necessary.
Before transfusion, the recipient’s and the donor’s blood are typed and cross-matched to avoid hemolytic transfusion reactions. Although many antigen systems are present on red blood cells, only the ABO and Rh systems are specifically tested prior to all transfusions. The A and B antigens are the most important, because everyone who lacks one or both red cell antigens has IgM isoantibodies (called isoagglutinins) in his or her plasma against the missing antigen(s). The isoagglutinins activate complement and can cause rapid intravascular lysis of the incompatible red blood cells. In emergencies, ...