The hemolytic activity of abo antibodies: Correlation between quantitative tests, complement-mediated hemolysis assay (CHUHE-P), and IgG subclasses.

ABO antibodies can activate complement and cause hemolysis, sometimes with ABO minor incompatible platelet or plasma transfusions. Donor low titres of anti-ABO are used to assess transfusion safety. However, the correlation between antibody titres (measured semi-quantitatively or quantitatively) and their ability to activate complement is unclear. This study aimed to correlate ABO antibody (IgM/IgG) titres and the presence of IgG1/IgG3 subclasses with complement-mediated haemolysis using the CHUHE-P assay (Complement Hemolysis Using Human Erythrocytes). Single-center blood group O donor samples were tested with semi-quantitative methods and classified in group 1 as low ABO titres if titre <100 and into group 2 as high ABO titre if titre >100. Testing included IgM/IgG antibody titration, the CHUHE-P assay, haemolysin test, and determination of IgG1/IgG3 subclasses. Group 1 had 21 and Group 2 had 56 blood donors. In Group 2, CHUHE-P positivity was not associated with IgM or IgG anti-A/B titres or haemolysin test results. IgG1 and IgG3 subclasses of anti-A were significantly associated with positive CHUHE-P. Significant differences between groups included CHUHE-P positivity (p < 0.001), IgG titres (p < 0.01) for anti-A, and CHUHE-P positivity (p < 0.001), IgM titres (p = 0.04), and haemolysin test (p = 0.02) for anti-B. In Group 1, 33% of anti-A and 23.8% of anti-B had positive CHUHE-P. This study aimed to compare the ability of anti-ABO antibodies to cause complement-mediated hemolysis measured by the CHUHE-P test and the results of semi-quantitative/quantitative titration assays, the presence of IgG1 and/or IgG3, and hemolysin test results, where we highlighted an inconsistent association between the methods; the positivity for CHUHE-P was associated with the subclasses of antibodies IgG1 and IgG3.