Histopathological and Immunohistochemical Study of Acute Tubular Injury in Native Kidney Biopsy

Acute tubular injury (ATI) is a common diagnosis on renal biopsy. There are no accepted parameters to assess the severity of injury or predict recovery. An objective histologic grading system would be of immense value in clinical practice. The macrophage response to injury involves the MI phenotype which is proinflammatory and M2 which is prorepair. The study of these macrophages could aid in studying the severity and the recovery.

A total of 58 native kidney biopsies with features of ATI and a minimum follow-up of 12 weeks were graded into mild, moderate and severe, using scores for simplification, sloughing, and mitosis. These scores and the density of macrophages stained with CD68, CD163, and HLA-DR were correlated with serum creatinine at presentation and with recovery. The effect of chronicity index as measured by glomerulosclerosis, tubular atrophy, and interstitial fibrosis and of co-morbidities of age, hypertension, and diabetes on the recovery pattern was also studied.

All three histologic scores and the grades of ATI showed positive correlation with the serum creatinine level. The densities of CD 68 + and CD163 + macrophages also showed a significant correlation with serum creatinine level. However, none of these these histological features nor the macrophage densities predicted clinical recovery. Age >60 years, hypertension, diabetes, and chronicity score on biopsy were indicators of partial and delayed recovery.

The histopathological semiquantitative scoring system can be used routinely to grade ATI. However none of the studied parameters predicted recovery.