Correlation Between C3d Assay and Single Antigen Bead Assay for Detection of Human Leukocyte Antigen Class II Antibodies

ABSTRACT

Background@#Detection of anti-human leukocyte antigen (HLA) antibodies is important during the selection of an appropriate donor prior to organ transplantation and also for monitoring the patients after transplantation. In this study, we compared antibodies detected via C3d assays, which monitors C3d complement-binding activities of HLA antibodies with those detected via single antigen bead (SAB) assays. @*Methods@#A total of 66 serum samples were tested in parallel by SAB assays (Immucor Transplant Diagnostics, USA) and C3d assays (Immucor) for the detection of HLA class II antibodies. The relationship between these two methods was analyzed based on the types, numbers, median fluorescent intensity (MFI) values, and positivity of the antibodies using MATCH IT! Antibody (Immucor) program. @*Results@#The number of antibodies obtained based on SAB and C3d assays was the highest with 24 samples (36.4%) in the 11–20 range and 23 (34.8%) in the 2–5 range detected via each assay. Among the SAB-positive antibodies, only 28 (6.4%) of the 440 antibodies with MFI ≤3,000 were C3d-positive, and 341 (61.3%) of the 556 antibodies with MFI ≥3,001 were C3d-positive. Whereas, among the 442 C3d-positive antibodies, SAB assays were positive except for 32 (7.2%) and 41 (9.3%) antibodies in the sections of MFI ≤500 and 1,001 ≤MFI ≤10,000, respectively. C3d-positive samples had higher maximum MFI values based on SAB assays, compared with C3d-negative samples. @*Conclusions@#MFI values of HLA class II antibodies detected through SAB assays in C3d-positive samples were higher than those in C3d-negative samples.