C3d Assay in Correlation With Single Antigen Bead Assay for Human Leukocyte Antigen Antibodies.

•The maximal MFI values of the SAB in the samples that were C3d assay-positive were significantly higher than those that were C3d assay-negative.•The MFI value of antibodies identified by SAB correlated with their positivity by C3d assay.•Only 0.4% of the antibodies with MFI <10,000 on SAB were identified by C3d assay with MFI >1000, whereas 59.4% of the antibodies with MFI >10,000 on SAB were identified by C3d assay with MFI >1000.