This term is a bit of a misnomer, but it is commonly applied to blood donors who have the blood type O-negative. These donors are considered “universal” because their red blood cells can generally be given to recipients with any ABO type (A, B, AB, or O), and because they are Rh-negative, their blood can be given to either Rh-negative or Rh-positive patients. For that reason, O-negative red cells were historically given in emergency situations (for example, in patients who have been seriously injured in car accidents or other trauma), before blood banks know the patient’s actual blood type. Today, in an effort to conserve O negative RBCs, most transfusion services actually use O-positive RBCs for emergency transfusions in males and females who are beyond child-bearing age.
While O-negative RBCs are ok to give to most patients, I call the term a “misnomer” because we sometimes have to deal with other blood group antibodies (so-called “unexpected antibodies“) when we are transfusing a patient, so not all O-negative blood can go to all patients (for example, if a patient had anti-K, and the O-negative donor was K-positive, the “universal” donor is suddenly incompatible with that patient). Despite this exception, O-negative blood donors (making up only 6-8% of the population) are incredibly important to all blood collection centers.
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