Visual interstitial fibrosis assessment as continuous variable in protocol renal transplant biopsies

INTRODUCTION: In current renal transplant pathology practice interstitial fibrosis is visually assessed in categories according to the Banff classification. As this has a moderate reproducibility, which is little ameliorated by morphometric analysis, we investigated whether visual renal fibrosis assessment is feasible on a continuous scale, i.e. as percentage affected area of the cortex.METHODS: Protocol renal biopsies taken at transplantation (n=125), three (n=73) and twelve months (n=88) after transplantation were visually scored in categories (Banff), and percentages for interstitial fibrosis (ci). Interobserver variation (ICC and weighted κ) was assessed, and morphometric analysis on Sirus Red stained sections was performed. Correlations between the different methods and their association with donor age and eGFR 1 year and 5 year post transplant were analyzed using Pearson's or Spearman's rho.RESULTS: Interobserver agreement was equivalent for Banffci and %ci (κ0.713 vs. ICC 0.792), and for BanffIF/TA and %IF/TA (κ0.615 vs. ICC 0.743). Both Banffci and %ci were associated with Sirius Red morphometry in three and twelve month. With all three methods, a significant correlation was found between donor age and fibrosis in the implantation biopsy, and between fibrosis in the 12 month biopsy and eGFR at 1 and 5 years (eGFR at 1 year: Sirius Red ρ-0.487, %ci ρ-0.393, Banffci ρ-0.413, all p<0.01, eGFR at 5 years: Sirius Red ρ-0.392, %ci ρ-0.333, Banffci ρ-0.435, all p<0.01.CONCLUSION: Interstitial fibrosis assessment on a continuous scale can be used next to scoring in categories according to the Banff classification in protocol renal transplant biopsies.