Value of C3d assay and IgG subclass in the prediction of the flow cytometry cross-match result for renal transplantation

The aim of this study is to compare the association and the predictive capacity of DSA MFI, complement fixing capacity (C3d assay) and IgG subclasses determination in the prediction of FCxM result. Methods: We used cryopreserved (-70C) sera from potential renal transplant recipients, containing DSA against their respective potential donors. All patients showed negative AHG-CDC CxM and either positive or negative FCxM. Class I and Class II HLA-DSA were determined by Luminex SAB. C3d were detected by Luminex (Lifecodes (R) Immucor), DSA IgG 1-4 subclasses were evaluated using monoclonal antibodies specific for IgG subclasses (Luminex). Results: 93 donor/recipient tests were evaluated; 32 (35.9%) patients presented at least one C3d + Ab, of which only 11 (11.8%) were donor specific. At least one IgG subclass was identified in 45 samples (48.3%). Twenty-seven FCxM tests (29%) were positive. On multivariate analysis HLA mismatches, the IgG subclass detection, DSA MFI and class II PRA remain associated to FCxM whereas C3d + Ab was not associated. For the FCxM prediction, the IgG subclass detection in combination with the DSA-MFI > 2800, had the best negative predictive value 93.9 (CI 95%, 84.2-100). Conclusion: Neither the C3d assay nor the IgG subclasses detection alone had an adequate predictive capacity for the FCxM. In the absence of IgG subclass detection and DSA-MFI < 2000, the probability of a negative FCxM was near 94%.