(P-TS-32) Cold Reacting Anti-M Antibodies in Cardiac Surgery with Cold Cardioplegia

Background/Case Studies: Anti-M allo-antibodies can be either warm reacting IgG or cold reacting IgM. Cold reacting anti-M is not considered clinically significant in routine transfusion practice as they do not interact with antigen at body temperature and do not necessitate issuing of M antigen negative RBCs. One exception is in patients during cardiac surgery requiring cold cardioplegia. Being an allo-antibody, cold reacting anti-Ms will not interact with the patient’s own RBCs when cooled however, there is a potential for agglutination or hemolysis of M-positive transfused cells in the cold. This concern was specifically raised by our pediatric heart surgery team where the cardio-pulmonary circuit is primed with donated RBCs. Given this uncommon potential risk in September of 2023 we developed a process to issue M antigen negative RBCs for patients undergoing cold, cardiac surgery, who are found have a cold reacting anti-M preoperatively. To verify cold anti-Ms as alloantibodies M phenotyping was routinely done on all anti-Ms starting February 2024.

Study

Design/Methods: We conducted a retrospective chart review of patients with cold reacting anti-M antibodies from our Blood Bank information system from 1/1/202- 3/2025 to assess frequency of cardiac cases requiring bypass and cardioplegia in this patient population both before and after our M-negative strategy was in place. Charts were evaluated for any evidence of concern for agglutination or hemolysis.

Results/Findings: 171 cold reacting anti-M antibodies were identified, 105 before using M neg units and 66 after our M negative plan. Ten patients (6%) had cardiac surgery requiring bypass and cold cardioplegia, 6 before and 4 in the group issued M-neg RBCs. These patients were cooled to a bypass circuit temperature of 26.9-33.4°C for a mean of 95 minutes. Three of the 6 historic cases were transfused RBCs during the cold bypass surgery. In the M-neg RBC cases, 2 of 4 were transfused during the cold surgical procedure. No case showed suspect agglutination in the bypass circuit from review of the perfusion notes. There were no clinical findings documented or laboratory results in the post-op period to suggest hemolysis and no patient had hemolysis specific lab assessments performed.

M phenotyping was done on 36 cases of which 35 (97%) were M negative confirming them as allo-antibodies. Eleven cases did not have phenotyping due to recent transfusion.

Conclusions: Cardiac surgery requiring cold cardioplegia and cardiopulmonary bypass in patients with cold reacting anti-M allo-antibodies is uncommon however issuing of M-antigen negative units when body temperature is being lowered is feasible and may prevent on bypass agglutination or hemolysis. Specifically assessing for hemolysis is needed to verify this precautionary practice.