Two cases of autoantibodies that demonstrate mimicking specificity in the Duffy blood group system

Two transfused Caucasian patients presented with possible delayed transfusion reactions. Both patients demonstrated an anti-Fya (Fy1) plus anti-Fyb (Fy2) pattern of reactivity in their sera. The patients' red blood cells (RBCs) were Fy:1,-2,3. Both had positive direct antiglobulin tests (DAT) with anti-IgG and -C3d. The serum antibodies reacted with the patients' RBCs drawn when the DATs were negative Both patients' serum samples showed reactivity with Fy:1,-2 (1+), Fy:-1,2 (3+), Fy:1,2 (3+) RBCs at the antiglobulin phase (AGT) but were nonreactive with Fy: -1, -2 RBCs. The antibodies in both cases were nonreactive with papain- or ficin-treated RBCs and reacted with Rhnull RBCs, which ruled out anti-Fy3 and anti-Fy 5 respectively. These cases suggest mimicking autoantibody specificities in the Duffy system one case may indicate that the degree of reactivity is dependent on the Duffy phenotype of the RBCs tested( Fy:-1,2 > Fy:1,2 > Fy: 1,-2). An unusual characteristic seen in both of these cases was hemolysis in the EDTA cell samples but none In the clotted samples.