The renal medulla in acute renal allograft rejection: comparison with renal cortex

A retrospective cohort study was undertaken to evaluate thediagnostic value of the renal medulla in acute renal allograftrejection (ARAR). One hundred and ninety-five biopsies from98 patients were randomly selected out of 565 transplant biopsies.Biopsies were graded blindly from Grade 0 (no rejection) toGrade 3 (severe rejection) using standard criteria; ARAR wasconfirmed by a fall in all cases of mean serum creatinine concentrationfrom 0.331 ± 0.182 to 0.184 ± 0.079 mmol/l, withanti-rejection therapy. In the 43 biopsies which contained bothcortex and medulla, the ARAR grades and the intensities of mononuclearcell, plasma cell, polymorphonuclear cell and eosinophil infiltrates,and of interstitial oedema and haemorrhage, were similar incortex and medulla (Spearman's Rank Correlation r=0.55–0.81,P < 0.001 ). The sensitivity, specificity and overall accuracyof medullary changes in predicting ARAR changes in the cortexwere 77%, 100% and 38%, respectively. Acute vascular rejectionchanges could not be compared between renal cortex and renalmedulla because of the anatomical differences between cortexand medulla. Further evaluation of ARAR in the all 195 biopsies,of which 188 had cortical tissue and 50 had medullary tissue,showed no significant differences in histological features (P> 0.05), except for more cortical biopsies with plasma cells(29%) than medullary biopsies with plasma cells (10%; P <0.02). It is concluded that: (1) ARAR histological changes aresimilar in cortex and medulla; (2) the predictive value of ARARmedullary changes for cortical rejection changes has low sensitivity(77%) and high specificity (100%). It is suggested that a predominantlynormal medullary renal biopsy in suspected rejection shouldbe repeated to obtain cortical tissue.