New serologic findings in a patient with ulcerative colitis and a warm autoantibody

IgG-RBC sensitization associated with serine proteases is the current prevailing hypothesis used to explain an uncommon phenomenon in which a positive DAT is obtained using the RBCs from a patient’s clotted blood sample but a negative DAT is obtained when testing RBCs from the patient’s unclotted sample. Similarly, the patient’s serum but not plasma will also be reactive by IAT against all RBCs tested. The majority of patients demonstrating this phenomenon have had a history of ulcerative colitis but no signs of hemolytic anemia. A case of IgG-RBC sensitization associated with serine proteases and a warm autoantibody in a 14-year-old Hispanic girl with ulcerative colitis is reported. The patient was admitted for severe anemia (Hb, 6.9 g/dL). On admission, pretransfusion testing of the patient’s serum and RBCs showed an ABO/Rh discrepancy between the forward typing and reverse grouping. The phenomenon of IgG-RBC sensitization associated with serine proteases was considered in the differential evaluation of the serum versus plasma typing discrepancy. To confirm the presence of the phenomenon of IgG-RBC sensitization associated with serine proteases, the plasma was clotted and converted to serum by the addition of thrombin. The initially nonreactive plasma was 2+ reactive when converted to serum. A warm autoantibody was also detected during the course of serologic evaluation. The patient was transfused with 2 units of incompatible RBCs with no adverse reaction observed. Immunohematology2009;25:160–164.