RBC transfusions are given to raise the hemoglobin levels in patients with clinically significant anemia or to replace losses after acute bleeding episodes.
PREPARATIONS OF RBCS FOR TRANSFUSION
Several types of preparations containing RBCs are available (whole blood, packed RBCs, frozen RBCs, or autologous non-frozen RBCs).
The advantage of whole blood for transfusion is the simultaneous presence of RBCs, 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 with hemorrhage or massive hemorrhage when more than 10 units of blood is required in a 24-hour period.
Packed RBCs 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 RBCs. One unit of packed RBCs 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 patients, including those who are critically ill, those undergoing cardiothoracic surgery or repair of a hip fracture, those with upper GI bleeding, and those with hematologic malignancy undergoing chemotherapy or hematopoietic cell transplant.
Packed RBCs 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 RBC phenotyped allogeneic donor for use in emergencies (such as in alloimmunized sickle cell patients). Frozen RBCs are also occasionally needed for patients with severe leukoagglutinin reactions or anaphylactic reactions to plasma proteins since frozen blood has essentially all WBCs and plasma components removed.
C. D. Autologous Packed RBCs
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 RBCs, 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 RBC 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 RBCs. In emergencies, type O/Rh-negative blood can be given to any recipient, but usually packed RBCs are ...