Kidney biopsy frequently detects kidney diseases other than diabetic nephropathy (DN) in individuals with type 2 diabetes mellitus (T2DM) who present with atypical proteinuria. A retrospective analysis published in Diabetes Care evaluated kidney biopsy findings and renal outcomes in patients with these clinical features.

The study reviewed 490 kidney biopsies performed at Shiga University of Medical Science Hospital between 2013 and 2024. From this cohort, 51 Japanese patients with T2DM met at least one criterion for proteinuria considered atypical for DN. Criteria included proteinuria without diabetic retinopathy, presence of hematuria, or persistent proteinuria despite strict glycemic and blood pressure control. The analysis assessed renal histopathology and examined changes in proteinuria levels and the rate of estimated glomerular filtration rate (eGFR) decline before and after biopsy.

Kidney biopsy identified typical DN in 17 patients (33.3%) and non-diabetic kidney disease (non-DN) in 34 patients (66.7%). Diagnoses in the non-DN group included membranous nephropathy, immunoglobulin A (IgA) nephropathy, renal sclerosis, interstitial nephritis, vasculitis, and other kidney diseases. Compared with the DN group, patients with non-DN were older and had a lower prevalence of diabetic retinopathy.

Following kidney biopsy and disease-specific therapy, the non-DN group showed significant improvement in proteinuria levels and in the rate of eGFR decline. The findings indicate that kidney biopsy can identify diverse kidney diseases in patients with T2DM who present with atypical proteinuria and may contribute to improved renal outcomes.