Evaluation of the relationship between the severity of interstitial fibrosis in diagnostic renal biopsies and disease progression in primary glomerular diseases.

This single-center retrospective cohort study divided 176 adults with biopsy-proven primary glomerulonephritis (GN) between 2014 and 2021 into 4 groups based on cortical interstitial fibrosis (IF) percentage. The primary outcome was disease progression, defined as a ≥40% decline in estimated glomerular filtration rate (eGFR) and/or the need for dialysis. The secondary outcome was complete remission, defined as proteinuria <300 mg/24 hours. Baseline proteinuria and serum creatinine increased with greater IF severity, while eGFR decreased. Kaplan-Meier analysis showed a higher risk of progression in patients with severe IF. After adjusting for glomerulosclerosis, baseline eGFR, proteinuria, and treatments, IF severity remained an independent predictor of progression (HR 3.15). IF was not independently associated with achieving complete remission. Stratified analyses suggested a stronger association in immunoglobulin-A (IgA) nephropathy, while results for focal segmental glomerulosclerosis (FSGS) and membranous glomerulonephritis (MGN) were inconclusive due to limited statistical power. In summary, the severity of IF on diagnostic biopsy is a strong and independent prognostic factor for disease progression in primary glomerular diseases, supporting its routine standardized assessment to improve risk stratification and personalized patient management.