Determination of accurate anti-A/-B titers is important for treatment selection in ABO-incompatible stem cell and solid-organ transplants. The standard method for ABO antibody titration is the conventional tube test (CTT). Dithiothreitol (DTT) is commonly used to inactivate the IgM antibody component. The aim of this study was to compare six different methods for ABO antibody titration and to observe the effectiveness of DTT on antibody estimation. A total of 90 healthy voluntary blood donors

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... re enrolled in this study, including 30 each for blood groups A, B, and O. Antibody titrations were performed and tested using the CTT-immediate spin (IS), CTT-antihuman globulin (AHG) with and without DTT, column agglutination technology (CAT)-IS, and CAT-AHG with and without DTT methods. Bead-CAT was used, and the positive cutoff value was set to 1+ for each method to determine the endpoint of the titer. The median values of anti-A/-B titers by IS were found to be higher than those values by AHG in CTT and CAT among group B and A individuals, whereas no statistically significant differences were observed in values from group O individuals for IS and AHG anti-A/-B titers, estimated by each method. Although there was positive correlation between the anti-A/-B titer results obtained using the CTT and CAT in all blood groups, testing using AHG showed poor agreement with and without DTT pretreatment (kappa value of 0.11 and 0.20, respectively). Moderate agreement was observed between CTT-IS and CAT-IS (kappa value of 0.46). Median anti-A/-B AHG titers were reduced by the use of DTT in all blood group samples. Significant differences in the interpretability of anti-A/-B titers were observed among different methods. A uniform approach for selecting the method for ABO antibody titration is highly recommended, and DTT pretreatment of plasma to neutralize IgM activity should be considered to obtain precise values of IgG anti-A/-B titers. Immunohematology 2021;37:25-32 .