Analysis of Renal Transplant Protocol Biopsies in ABO‐Incompatible Kidney Transplantation

Numerous studies have shown that protocol biopsies have predictive power. We retrospectively examined the histologic findings and C4d staining in 89 protocol biopsies from 48 ABO‐incompatible (ABO‐I) transplant recipients, and compared the results with those of 250 controls from 133 ABO‐compatible (ABO‐C) transplant recipients given equivalent maintenance immunosuppression. Others have shown that subclinical rejection (borderline and grade I) in ABO‐C grafts decreased gradually after transplantation. In our study, however, subclinical rejection in the ABO‐I grafts was detected in 10%, 14% and 28% at 1, 3 and 6–12 months, respectively. At 6–12 months, mild tubular atrophy was more common in the ABO‐C grafts whereas the incidence of transplant glomerulopathy did not differ between the two groups (ABO‐C: 7%; ABO‐I: 15%; p = 0.57). In the ABO‐I transplants, risk factors for transplant glomerulopathy in univariate analysis were positive panel reactivity (relative risk, 45.0; p < 0.01) and a prior history of antibody‐mediated rejection (relative risk, 17.9; p = 0.01). Furthermore, C4d deposition in the peritubular capillaries was detected in 94%, with diffuse staining in 66%. This deposition, however, was not linked to antibody‐mediated rejection. We conclude that, in the ABO‐I kidney transplantation setting, detection of C4d alone in protocol biopsies might not have any diagnostic or therapeutic relevance. This study of protocol biopsies in ABO‐incompatible transplant recipients, compared to those of ABO‐compatible transplant recipients, showed an increased incidence of subclinical rejection at 6 to 12 months after transplantation and revealed that C4d deposition in the peritubular capillaries was more common.