Successful transfusion of antigen positive blood to alloimmunised patients using a monocyte monolayer assay

Providing adequate transfusion support for alloimmunised patients for whom antigen negative blood is not readily available is hampered by the risk of a haemolytic reaction. The monocyte monolayer assay (MMA) has shown good correlation between the antibody clinical significance and the fate of antigen positive blood.

From 2006 to 2013, the clinical significance of red cell alloantibodies produced by 61 patients was evaluated using a MMA; and antigen positive blood offering the best survival advantage was selected for transfusion following a secondary MMA crossmatch. Post-transfusion, patients were evaluated for clinical signs of haemolysis.

Overall, 19 of 61 (31·1%) of our antibodies were potentially clinically significant, with a monocyte index (MI) > 5%. There was no correlation between the clinical significance as showed by the MMA, and the specificity of the antibody or the strength of reactivity at antihuman globulin (AHG) phase. Using the MMA as a secondary crossmatch method, 31 alloimmunised patients (including: eight anti-hr(B), four anti-Yt(a), one each anti-Rg1, -Co(a), Er(a), Le(b), -LW, -Sl1) received 103 antigen positive blood units with no clinical sign of a post-transfusion reaction. For three patients (one each anti-Jo(a), -AnWj, unidentified 'HTLA'), initial MMA was performed as part of an investigation of a suspected haemolytic reaction. In each case, the MMA accurately identified the unit responsible for the reaction.

Used as a crossmatch surrogate, the MMA provided valuable information in the decision of transfusing antigen positive blood to alloimmunised patients, avoiding delay because of the search of rare antigen negative units.