Case report Naturally occurring anti-M with high thermal amplitude complicating ABO blood grouping Vivek Ranjan, Kamini Khillan* Department of Transfusion Medicine, Sir Ganga Ram Hospital, New Delhi, 110060, India A R T I C L E I N F O Article history: Received 28 November 2017 Accepted 19 February 2018 Available online 20 February 2018 A B S T R A C T Anti-M is fairly common naturally occurring antibody that is usually active at a temperature below 37  C, with an optimum temperature of 4  C rarely causing haemolytic transfusion reaction or haemolytic disease of new born and can generally be ignored in transfusion practice. We report a case of 28 year old unmarried female blood donor who had an unexpected reaction in blood grouping due to anti-M that posed a problem for us in the interpretation of her blood group. We also reviewed literature to find out the significance of anti-M antibody. © 2018 Sir Ganga Ram Hospital. Published by Elsevier, a division of RELX India, Pvt. Ltd. All rights reserved. 1. Introduction The MN blood group system was discovered in 1927 when Landsteiner and Levine deliberately immunised rabbits with human red cells. 1 The MN blood group system was expanded in 1947 with the discovery of anti S and anti s in 1951. 2 Anti- M is the most commonly encountered antibody of MNS system. 3 It is a naturally occurring antibody originally described by Wolff and Jhonsson in 1933. 4 Most anti-M are not active at 37  C and can generally be ignored in transfusion practice. They are most active at 4  C or a temperature below 37  C and are considered to be clinically insignificant. 5 It appears to be more common in infants than in adults. Our experience with regards to anti-M has been different and this was the first case of anti-M in past two years encountered during routine ABO/Rh typing reacting at 37  C and complicating the interpretation of blood grouping results. 2. Case report Routine ABO/Rh blood typing of healthy blood donors were performed by column agglutination gel technique (Diaclone ABO/ D + reverse grouping, BioRad ID micro typing system). A 28 year old unmarried female blood donor sample showed unexpected agglutination reaction with forward grouping A Rh (D) +ve while reverse grouping ‘O’ (Fig. 1). Donor questionnaire form was checked for previous history of blood transfusion and found that she never received any blood transfusion in past. After excluding the possibilities of technical error the grouping was then performed by the tube technique with additional O cell in reverse grouping and we found the same reaction in forward grouping and pan reactivity in all three cells (+4 in B & +2 in A and O cells). Further reverse grouping was done with all three cells and tubes were incubated at 4  C, room temperature and 37  C. We found pan reactivity in all three temperatures with enhancement of agglutination reaction at 4  C (+4) indicating the presence of some cold antibody reactive at 37  C (+1). The 37  C test was carried out in strict warm conditions and interpretation done before allowing the tube to cool down to room temperature. Direct antiglobulin test and auto control were negative by both gel and conventional tube method ruling out the obvious possibility of autoantibody. Antibody screening was then performed with three cell panel (Diascreen I, II, III BioRad micro typing system) and was found to be positive (+4) with panel II and III while negative with panel one. Antibody showed the pattern of anti-M using eleven identification cell panels (ID DiaPanel BioRad) by manual method. To further confirm the presence of anti-M, screening and identification was performed using enzyme treated cells (ID Diapanel P BioRad) and the reaction was negative with all the cells. The A and B cell negative for M antigen were used for reverse typing and the result clearly indicated. A group of the donor as well as supporting the fact that the unexpected alloantibody causing discrepancy was anti-M. * Corresponding author. E-mail address: kamini.khillan@sgrh.com (K. Khillan). https://doi.org/10.1016/j.cmrp.2018.02.004 2352-0817/© 2018 Sir Ganga Ram Hospital. Published by Elsevier, a division of RELX India, Pvt. Ltd. All rights reserved. Current Medicine Research and Practice 8 (2018) 71–72 Contents lists available at ScienceDirect Current Medicine Research and Practice journal homepage: www.else vie r.com/locate /cmrp