Warm-Reactive Autoantibodies - Reporting:

Strongly reactive warm-reactive autoantibodies, particularly those that are accompanied by C3 deposition, tend to be more likely to cause clinically overt hemolysis. However, this correlation is not absolute: weakly-reactive autoantibodies may be clinically significant while strongly reactive autoantibodies may be detected in otherwise completely well individuals.

The clinical significance of an autoantibody can therefore only be reliably determined by assessing the patient for signs of hemolysis. In addition to cueing the patient’s physician to order these investigations, the blood transfusion service should also warn the clinical team that all crossmatched units will be incompatible.

Many clinicians will be uneasy transfusing incompatible units to their patients; however, one should never withhold a transfusion in a patient with a warm autoantibody if a clinical indication for transfusion exists. It is therefore important to inform the physician what steps have been taken to ensure that any transfused units will not cause or worsen hemolysis due to incompatibility from minor blood group alloantibodies. Such precautions may include:

  • Performance of adsorption procedures to identify underlying alloantibodies.
  • Selecting RBCs that are prophylactically matched for common clinically significant alloantibodies (ie., matched for C, c, E, e, K at a minimum, and Fya, Fyb, Jka, Jkb, and S if possible).

As adsorption studies may take many hours to complete, reliance on prophylactically matched RBCs alone may be required for initial transfusion support. Selection of “least incompatible” units, however, is no longer advised, as it provides a false sense of security to the clinician: there is no evidence that the strength of reaction by crossmatch predicts the rate with which the transfused RBCs will be cleared from circulation.

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