Focal C4d staining in peritubular capillaries and kidney graft survival: results of a retrospective study

A diffuse positivity (>or=50%) of C4d in kidney graft peritubular capillaries (PTC) significantly correlates with the presence of acute or chronic antibody-mediated rejection. In contrast, significance of a "focal" deposit (10%-50%) is not yet completely defined. The purpose of this study was to assess the impact of focal positive C4d staining on graft survival. We retrospectively reviewed 63 renal biopsies in 54 kidney transplant recipients. They were performed between January 2005 and December 2008 because of graft impairement, namely, a significant increase in serum creatinine and/or urinary protein. C4d positivity was assessed by immunohistochemistry on paraffin-embedded sections, in combination with conventional histopathologic evaluation. Biopsies were classified as negative (<10%) versus with focal (10%-50%) or diffuse deposits (>50%). Cumulative survival was calculated by the Kaplan-Meier method, and Cox regression analysis was used for the multivariate analysis. Focal C4d staining in PTC significantly correlated with worse graft survival (P = .006), similarly to diffuse C4d staining. On multivariate analysis, focal C4d staining prognostically correlated with graft survival, but not recipient or donor age, prior transplantation, number of HLA mismatches or the presence of tubulitis in the sample. Focal C4d staining was associated with worse graft survival.