Spectrum of clinically significant anti-M antibody in patients requiring transfusion

Aims: The study aimed to determine the frequency and serological characteristics of anti-M antibody in patient population. Methods: It was a retrospective study over for a period of two years (April, 2016 to March, 2018). Blood grouping was performed by tube technique. In case of incompatible cross-match, antibody screening and identification were performed using LISS Coombs’ anti-human globulin (AHG) gel cards (Bio-Rad, Switzerland). Di-thiothreitol (DTT) treatment was also performed to demonstrate the existence of a potentially clinical significant IgG antibody. Results: The frequency of anti-M antibody was 0.05% in patients (51 out of 101,364 requisitions). DTT treatment could be done in 12 samples which showed it was IgM type in 11 (91.7%) and mixture of IgM and IgG type in 1 (8.3%) case. Transfusion history was present in 21 (41.2%), absent in 13 (25.5%), and not known in 17 (33.3%) patients. M antigen phenotyping in 42 patients showed that 41/42 patients were M-negative (six of them gave a “mixed-field” agglutination due to recent transfusion of M+ PRBC unit). The 42nd patient was typed as M+ which could be again due to history of recent transfusion of PRBC. Conclusion: Most of the anti-M antibodies were IgM type, however, serological characterization revealed the IgG type also which were found to be reactive at 37°C in AHG phase and thus clinically significant.