Alloimmunization following blood transfusion.

: Although it has been 20 years since Rh immunoglobulin (Rhlg) was widely introduced in the United States, anti-D still remains as a frequent alloantibody found in hospital patients. Currently, anti-D is second in frequency only to anti-K as an alloantibody of clinical significance. Estimation of alloantibody frequencies in hospital patients reveals a gradual decline in the frequencies of anti-D and anti-CD, whereas anti-K, anti-E and anti-Jka show increases in relative and absolute frequencies. This phenomenon probably reflects the optimum use of Rhlg and more aggressive transfusion treatment of patients as indicated by the red cell use factor: (Red cell transfusions -- autologous transfusions)/admissions. Such a practice may be the result of the increasing severity of illness observed in patients admitted to hospitals. Alloimmunization due to donor white blood cells, platelets, and serum proteins also frequently follows the transfusion of homologous blood. These problems, which may pose additional risks to the transfusion recipient, are reviewed.