Evolution of glomerular filtration rate in proteinuric NIDDM patients

OBJECTIVE: To evaluate, by means of a precise method, the rate of decline of glomerular filtration rate in proteinuric non-insulin-dependent diabetic (NIDDM) patients. RESEARCH DESIGN AND METHODS: The study was comprised of seven NIDDM patients who visited an outpatient clinic and had a 24-h urinary protein excretion rate greater than or equal to 500 mg in the absence of heart failure, urinary tract infection, or other nephropathies. RESULTS: Glomerular filtration rate (51Cr-labeled EDTA, single-injection protocol) and 24-h proteinuria (turbidimetric method) were assessed at periodic intervals (2-6 mo). Correlation of the measurements with time (Pearson's r, with Student's t test used to assess the significance, alpha = 0.05) was used to evaluate the trend of evolution of glomerular filtration rate. Renal biopsies were performed in four patients. In three of four patients, renal histopathology was consistent with the diagnosis of diabetic nephropathy (in the 4th patient measurements were not satisfactory). Neither glomerular filtration rate nor proteinuria correlated significantly with time, except in one patient who had multiple myeloma. CONCLUSIONS: The decline of glomerular filtration rate in proteinuric NIDDM patients is different from that observed in insulin-dependent diabetic patients, which is probably much slower.