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 identify group O donors with high titres of anti‐A and anti‐B. However, critical immunoglobulin M/ immunoglobulin G (IgM/IgG) titres remain unclear. This...

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 identify group O donors with high titres of anti‐A and anti‐B. However, critical immunoglobulin M/ immunoglobulin G (IgM/IgG) titres remain unclear. 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. 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. An association between anti‐A and anti‐B IgM titres and haemolysin were demonstrated (P < .001). IgM titres in plasma samples from platelet components correlated 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). 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

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