Routine RBC compatibility testing includes ABO and RhD typing, an antibody screen for IgG non-ABO RBC antibodies, and a RBC crossmatch.
RBCs must be ABO compatible to avoid intravascular hemolysis, and Rh D-negative patients should receive D-negative RBCs to avoid anti-D alloimmunization.
Rh, Kell, Kidd, Duffy, and some other non-ABO antibodies can hemolyze transfused RBCs; 1% of all patients and 5% to 20% of heavily transfused patients have such antibodies.
The American Society for Anesthesiologists' Practice Guidelines for Blood Component Therapy state that “red blood cell transfusion is rarely indicated when the hemoglobin concentration is greater than 10 g/dL and is almost always indicated when it is less than 6 g/dL.”
Traditionally, patients with cardiovascular disease and anemia were considered to be at significant risk of tissue ischemia and therefore thought to benefit from higher hemoglobin goals in the perioperative and critical care setting. Reviews have since contradicted these findings by documenting the safety of hematocrits <24% during cardiac surgery with cardiopulmonary bypass.
Patients with cerebrovascular disease or acute neurologic illness such as ischemic stroke, subarachnoid hemorrhage, and traumatic brain injury are at significant risk for secondary injury from tissue hypoxia. (Evidence indicates that a hemoglobin level <9 g/dL is independently predictive of a poor outcome, especially in patients with cerebrovascular injury.)