Monocyte monolayer assay in pre-transfusion testing: A magic key in transfusing patients with recurrent bad cross-match due to alloimmunization.

Background: The monocyte monolayer assay (MMA) is an in-vitro assay that can predict the outcome of blood transfusion of antigen positive units when serologically compatible blood is not available.
Materials and Methods: Fifty-four patients testing positive by the antibody screening test using gel agglutination were further examined by the alloantibody identification panel to determine alloantibody specificity. After determining and categorizing the antibodies, patients' samples were examined using the MMA to determine the clinical significance of the detected alloantibodies. We also tested 2 seeding methods (24-well cell culture plates versus 8-well chamber-slides) and 3 visualization/staining techniques (unstained phase contrast, Leishman and Giemsa staining).
Results: 35 out of the 54 cases (64.8%) had a monocyte index of >5% which is predictive of occurrence of hemolytic reaction after transfusion; 23 cases with antibodies known to be clinically significant [anti-C, anti-E, anti-c, anti-K, anti-Fy(a), anti Fy(b), anti-JK(b)], 2 with Anti-M specificity, 7 cases with autoantibodies and 3 cases with multiple antibodies. On the other hand, 19 out of the 54 (35.2%) cases included in the study showed a monocyte index of <5% which is predictive of absence of hemolytic reaction after transfusion. The 8-well chamber-slides were better than the 24-well culture plates, as the latter showed a lot of un-phagocytosed RBCs in the background. Also, Leishman staining was better than Giemsa staining with better and clearer differentiation between the RBCs, monocytes and phagocytic vacuoles.
Conclusion: MMA can be used as a surrogate cross-match test for the selection of blood units in cases where antigen-negative blood units are not available.
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