ABO Blood Group Discrepancy Due to An Unusual Naturally Occurring, Clinically Significant Anti-M antibody: A Case Report

ABO blood group is the most clinically significant blood group determined by forward and reverse grouping, which should match with each other. Any discrepancy between the forward and reverse grouping should be resolved to avoid incompatible transfusion reactions. Anti-M is a naturally occurring antibody that can lead to ABO discrepancy triggering a challenge for the blood bank. The objective of this case report was to present a rare case of anti-M leading to ABO discrepancy. A 2-year-old girl, diagnosed with right canine space cellulitis, was admitted for incision and drainage and tooth extraction under general anaesthesia. Her ABO blood group showed discrepancy where forward grouping was A, but reverse grouping was O with 4+ reaction in both A-cell and B-cell. Repeat testing with a new sample showed similar results. The patient’s probable Rh genotype was CDe/Cde (R1R1). The direct Coombs test and autocontrol were negative. She had no prior sensitization events. Antibody screening was positive and antibody identification revealed anti-M with a wide thermal range from 4°C to 37°C. MN phenotype was NN. Subsequent testing showed that the reverse grouping reagent A-cell possessed M-antigen and the positive reaction in reverse grouping was due to anti-M rather than anti-A. Repeat reverse grouping using M-antigen negative A-cells was negative. Crossmatch with M-antigen negative blood was compatible. Any ABO discrepancies should be resolved before transfusion. Anti-M reactive at 37°C is a clinically significant antibody. Therefore, careful interpretation of the results and a thorough analysis of the patient’s clinical history, previous blood group or transplant or transfusions history is extremely important.International Journal of Human and Health Sciences Vol. 06 No. 01 January’22 Page: 143-146