SHORT COMMUNICATION Comparison of ABO antibody titration, IgG subclasses and qualitative haemolysin test to reduce the risk of passive haemolysis associated with platelet transfusion Eduardo Peres Bastos 1 | Lilian Castilho 1,2 | Carolina Bonet Bub 1 | Jose Mauro Kutner 1 1 Departamento de Hemoterapia e Terapia Celular, Hospital Israelita Albert Einstein, S~ao Paulo, Brazil 2 Universidade Estadual de Campinas, S~ao Paulo, Brazil Correspondence Carolina Bonet Bub, Hospital Israelita Albert Einstein—Av. Albert Einstein, 627—Jardim Leonor, S~ao Paulo—SP, Brazil 05652-900. Email: carolina.bub@einstein.br Abstract Background: One of the strategies used to reduce the risk of haemolysis due to ABO-minor incompatible platelet transfusions is to perform a screening test to iden- tify group O donors with high titres of anti-A and anti-B. However, critical immuno- globulin M/ immunoglobulin G (IgM/IgG) titres remain unclear. Objective: This study aimed to determine IgM titres of anti-A and anti-B in individual donor serum vs platelet products plasma and identify a possible association between IgM/IgG titres, haemolysin test and IgG subclasses in Brazilian blood donors from group O. Methods: IgM anti-A and Anti-B titration tests were performed on single-donor serum and platelet product plasma by gel agglutination (GA) at room temperature. For IgG anti-A and anti-B titration, serum was first treated with 0.01 M dithiothreitol (DTT), and the test was performed by GA with incubation at 37  C. Dilution of 1:64 as the cut-off was considered for both IgM/IgG. The qualitative haemolysin test was performed in tube, adding AB fresh serum, with incubation at 37  C. IgG subclasses were determined by GA using specific monoclonal antibodies. Results: An association between anti-A and anti-B IgM titres and haemolysin were demonstrated (P < .001). IgM titres in plasma samples from platelet components cor- related to those in single-serum samples. IgG1/IgG3 subclasses were associated with total haemolysis and titres above 64, whereas IgG2/IgG4 subclasses were associated with the absence of haemolysis and titres below 64 (P < .001). Conclusion: Our data suggest that a value of 64 as a critical titre can be used as a screening test of anti-A and anti-B IgM to prevent transfusion reactions. This can be a safe and cost-effective approach for managing ABO-incompatible platelet transfusions. KEYWORDS ABO antibody titration, ABO haemolysin, ABO isohemagglutinins, platelet transfusion Received: 27 February 2020 Revised: 7 April 2020 Accepted: 1 May 2020 DOI: 10.1111/tme.12687 Transfusion Med. 2020;1–7. wileyonlinelibrary.com/journal/tme © 2020 British Blood Transfusion Society 1