The impact of anti-M antibodies on patient blood typing and transfusion safety: a retrospective study.

Background: Anti-M antibodies are a group of frequently detected, naturally occurring antibodies, most of which are immunoglobulin M (IgM) antibodies, inactive at 37 °C, and clinically insignificant in blood transfusion experiments, except for their effect on blood groups. Anti-M antibodies may be clinically significant in some exceptional cases, however, such as cardiac surgery, when the core body temperature drops, resulting in hemolytic transfusion reactions. The present study was conducted to explore the interference caused by the presence of anti-M antibodies on blood group identification, analyze the necessity of detecting such antibodies in advance for transfusion compatibility testing and clinical transfusion, and explore the importance of O-antigen erythrocytes in routine blood typing, especially in screening for IgM-class antibodies.

Methods: This study was initiated by collecting blood typing specimens from January 2021 to December 2023 in the Blood Transfusion Department, where the O cell control tubes showed agglutination in the blood group reverse serotyping, which were ultimately determined to be influenced by the anti-M antibodies. This study further analyzed the absorption of plasma using M antigen-positive type O erythrocytes, followed by repeat ABO typing with either the absorbed plasma or standard reverse grouping erythrocytes without M antigen. Our subsequent steps included a cross-matching test with manual tube testing, the Polybrene method, and antiglobulin test, monitoring of the hemoglobin value after transfusion.

Results: A total of 11 patients had anti-M antibodies detected in their serum. Among these 11 patients, 9 had blood type discrepancies identified during blood typing, and the other 2 cases were identified as type O. We saw 4 cases of IgM-type antibodies, 1 case of IgG-type antibodies, and 7 cases of IgM-type and IgG-type antibodies. The forward and reverse typing of 9 samples showed consistent results after serum reverse typing was rechecked by O cell absorption. Cross-matching was compatible with blood donors without M antigen, and 7 of these patients were treated with transfusion, all of whom had elevated hemoglobin levels after transfusion, with no adverse transfusion reactions.

Discussion: In specimens with irregular anti-M antibodies, serum absorption can be used to eliminate the interference caused by the irregular antibodies and obtain the correct experimental results. Moreover, the addition of type O red blood cells in the experiment can improve the detection rate of partial antibodies. For specific patients, such as individuals undergoing surgery, regardless of whether the antibody reacts at 37 °C, we recommend choosing M antigen-negative donors for blood transfusion to ensure the safety of blood transfusion for patients in clinical settings.