Detection of mixed‐field agglutination due to loss of red cell antigen in hematopoietic malignancy

Abstract

Red blood cell (RBC) transfusions were requested for a 60-year-old woman with hypoplastic myelodysplastic syndrome (MDS) treated with cyclosporine to reverse progressive pancytopenia. During routine forward grouping, the patient typed as group A, but with mixed-field reactivity in the anti-A column of the gel card (Left panel, red box). Reverse typing with Al and B cells in the right-most two gel columns was consistent with blood group A. Common causes of mixed-field agglutination were excluded, including transfusion within the last 3 months and the presence of A-sub-groups. To further investigate the mixed-field result, we utilized an automated fluorescence cytometric blood typing method previously described by our group1'2 (Right panel. The density of antigen expression [PE fluorescence] increases from left to right; isotype control [iso] is purified polyclonal IgM). These studies showed that the patient's RBCs were group A, but could be separated into two distinguishable subpopulations that differed in their levels of A antigen expression (red line). Note that the population on the left (dashed arrow), with lower PE fluorescence, nonetheless does express residual A antigen as it is shifted to the right of the isotype control reaction (blue line). The population on the right (solid arrow) shows more usual levels of A antigen expression. In agreement with the typing results on the gel card, the patient's RBCs were negative for B antigen (black line). Thus, the mixed-field reaction seen on the gel card was due to the loss of A-antigen expression on a subpopulation of the patient's RBCs-a phenomenon that has been described in MDS patients. In addition to routine blood typing 1,2 , fluorescence cytometry is a powerful method for resolving complicated immunohematologic problems.