Histopathological Findings in Protocol Biopsies of Transplanted Kidneys

Overview

Fourty eight patients with cadaveric kidney allografts treated by cyclosporin A (CSA) or tacrolimus(FK506) underwent protocol graft biopsies at 1, 3 and 12 months after transplantation, and110 biopsy specimens were obtained. Histologic diagnosis was made according to the Banff scheme.The main cause of the graft instability at 1 and 3 months was acute clinical rejection, thesebiopsies showed all known histological patterns of tubulointersticial and vascular rejection. Acutetubular nephropathy was found in 13% and borderline changes or nephrotoxicity in 8.7% ofinstable grafts. Specifically, we focused on the occurence of subclinical rejection and toxic reactionsin stable renal allografts. Of these, 36.1% showed histological patterns of acute tubulointersticialand vascular rejection. The Banff score of subclinical rejection was significantly lower thanin clinically apparent rejection. CSA and tacrolimus nephrotoxicity were seen in 14.2%, 19.5% and27.2% of specimens at 1, 3 and 12 months, respectively. In over one half of the identified cases ofnephrotoxicity neither increased level of immunosuppresion nor features of allograft dysfunctionwere found. At 12 months, 45.5% of specimens showed mild chronic transplant nephropathy and18.1% moderate chronic transplant nephropathy. Normal morphology was found in 36.4% of biopsies.We found a high prevalence of subclinical rejection and nephrotoxicity in the studied cohort.We conclude that protocol biopsy is a reliable method in the diagnosis of clinically silent, aswell as clinically apparent, disorders of the transplanted kidney.

Key words:
renal transplantation - protocol biopsy - subclinical rejection - nephrotoxicity