A discrepancy in ABO typing occurs when the front and back types do not agree. Resolving the discrepancy requires an evaluation of both the front and back typings.


Front type: testing the patient's red blood cells with reagent antisera


Causes of unexpected positive reactions:

(1) chimera following bone marrow transplant

(2) polyagglutinable red blood cells

(3) acquired A or B substance

(4) recent transfusion

(5) red blood cells coated with protein (rouleaux, etc), often due to inadequate washing

(6) autoantibody


Causes of unexpected negative reactions:

(1) decreased antigen expression on the red blood cells

(2) inactivated antisera

(3) masked antigenic sites due to protein or autoantibody


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