Clinicopathological Characteristics and Kidney Outcomes in Biopsy-Confirmed Acute Interstitial Nephritis

Acute interstitial nephritis (AIN) is a significant cause of acute kidney injury, with varying etiologies and outcomes. This study aimed to examine the causes, clinical characteristics, management, and kidney outcomes in patients with biopsy-confirmed AIN.

A retrospective review was conducted on 166 patients diagnosed with AIN through kidney biopsy at Mayo Clinic between 2012 and 2023. Demographic, clinical, laboratory, and pathological data were collected. The primary outcome was kidney function recovery within the first 6 months. Statistical analyses included univariable and multivariable logistic regression, Kaplan-Meier survival analysis, and Cox proportional hazards modeling.

Medications were the primary cause of AIN (67%), followed by autoimmune diseases (20%) and infections (6%). Within 6 months, 76% of patients achieved kidney recovery. Multivariable analysis indicated that moderate to severe interstitial fibrosis and tubular atrophy (IFTA) and dialysis requirement were associated with nonrecovery, whereas a prebiopsy diagnosis of AIN was positively associated with kidney recovery. Drug-related AIN had higher recovery rates compared to all other causes (81% vs. 66%, P = 0.04), and moderate to severe IFTA and dialysis need remained significant predictors of decreased recovery. Steroid therapy, used in 81% of patients, did not significantly influence kidney recovery in the overall cohort or in drug-induced AIN.

This study provides insights into the characteristics and outcomes of biopsy-confirmed AIN. IFTA and dialysis requirement were significant factors associated with worse kidney outcomes. These findings may help inform clinical management and prognostication in patients with AIN.