The renal histopathology of nonproteinuric kidney impairment: a three center experience.

Proteinuria is a biomarker of kidney injury that typically results from glomerular and/or tubulointerstitial disease. Whereas kidney impairment with normal urinary protein excretion is usually less focused and understudied. We conducted a retrospective review of the renal histopathology of the patients with variable degrees of unexplained renal insufficiency but with normal range proteinuria between 2014 and 2024 of  three university teaching hospitals in Shenzhen city of Southern  China. Patients with kidney dysfunction of undetermined or uncertain etiology and with normal urinary protein excretion (defined by a 24hr urinary protein excretion < 150 mg or spot urinary protein to creatinine ratio [PCR] < 150 mg/g) were enrolled and analyzed. In a total of 2405 patients, 53 (2.2%) fulfilled the inclusion criteria  (male/female 40/13, age 47.3 ± 14.3 years) with a mean eGFR of 46.6 ± 16.8 ml/min per 1.73 m. Glomerular disease (GD) was the most frequent pathological finding identified in 23 (43.4%) patients, while 19 (35.8%) cases  showed tubulointerstitial disease (TID) and 11 (20.8%) patients exhibited small vascular disease (SVD). Patients in the TID had the lowest mean eGFR and the highest numerical 24hr urinary protein excretion among the three groups. The incidence of acute kidney injury was significantly higher in TID than in other two groups. The patients in the SVD group had the highest fraction of underlying hypertension. Kidney dysfunction with normal range proteinuria may be related with, in descending order of probablity,  glomerular, tubulointerstitial and small vascular diseases. Renal biopsies were proved useful in informing therapeutic choice, long-term management and in predicting prognosis in this setting.