Histological Features of Kidney Allograft Biopsies According to Metabolic Acidosis Status: A Biopsy-Based Single-Center Observational Study

Metabolic acidosis is common after kidney transplantation and has been linked to adverse renal outcomes. However, its relationship with histological injury in kidney allografts remains poorly characterized. We aimed to explore the association between metabolic acidosis and histopathological features in kidney allograft biopsies. This single-center, cross-sectional observational study included 63 adult kidney transplant recipients who underwent clinically indicated allograft biopsies. Metabolic acidosis was defined as a serum bicarbonate level < 22 mmol/L at the time of biopsy. Histological lesions were assessed according to the Banff classification. Lesion severity was evaluated using descriptive statistics, nonparametric comparisons, ordinal logistic regression, and multivariable logistic regression models adjusted for renal function, proteinuria, and time from transplantation. Sensitivity analyses additionally adjusted for hemoglobin and donor-related variables. Patients with metabolic acidosis exhibited numerically higher severity scores for both acute inflammatory lesions and chronic histological changes, including total inflammation and interstitial fibrosis/tubular atrophy (IFTA). Across ordinal analyses and multivariable regression models, consistent directional trends toward a greater histological injury burden were observed among acidotic patients; however, none of these associations reached statistical significance, and confidence intervals were wide. Sensitivity analyses yielded directionally consistent effect estimates. In this biopsy-based analysis, metabolic acidosis showed consistent directional trends toward a higher burden of inflammatory and chronic histological lesions, although these findings did not reach statistical significance.