THE RENAL MEDULLA IN ACUTE RENAL-ALLOGRAFT REJECTION - COMPARISON WITH RENAL-CORTEX

A retrospective cohort study was undertaken to evaluate the diagnostic value of the renal medulla in acute renal allograft rejection (ARAR). One hundred and ninety-five biopsies from 98 patients were randomly s elected out of 565 transplant biopsies. Biopsies were graded blindly f rom Grade 0 (no rejection) to Grade 3 (severe rejection) using standar d criteria; ARAR was confirmed by a fall in all cases of mean serum cr eatinine concentration from 0.331+/-0.182 to 0.184+/-0.079 mmol/l, wit h antirejection therapy. In the 43 biopsies which contained both corte x and medulla, the ARAR grades and the intensities of mononuclear cell , plasma cell, polymorphonuclear cell and eosinophil infiltrates, and of interstitial oedema and haemorrhage, were similar in cortex and med ulla (Spearman's Rank Correlation r=0.55-0.81, P<0.001). The sensitivi ty, specificity and overall accuracy of medullary changes in predictin g ARAR changes in the cortex were 77%, 100% and 38%, respectively. Acu te vascular rejection changes could not be compared between renal cort ex and renal medulla because of the anatomical differences between cor tex and medulla. Further evaluation of ARAR in the all 195 biopsies, o f 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 biopsie s with plasma cells (10%; P<0.02). It is concluded that: (1) ARAR hist ological changes are similar in cortex and medulla; (2) the predictive value of ARAR medullary changes for cortical rejection changes has lo w sensitivity (77%) and high specificity (100%). It is suggested that a predominantly normal medullary renal biopsy in suspected rejection s hould be repeated to obtain cortical tissue.