Objective: The structural basis of normoalbuminuric renal insufficiency in patients with type 2 diabetes remains to be elucidated. We compared renal biopsy findings in patients with type 2 diabetes and estimated glomerular filtration rate (eGFR) and measured GFR of <60 mL/min/1.73 m2, associated with either normo-, micro-, or macroalbuminuria.
Research Design and Methods: In patients with normo- (n = 8) or microalbuminuria (n = 6), renal biopsies were performed according to a research protocol. In patients with macroalbuminuria (n = 17), biopsies were performed according to clinical indication. Findings were categorized according to the Fioretto classification: category 1 (C1), normal/near normal; category 2 (C2), typical diabetic nephropathy (DN) with predominantly glomerular changes; and category 3 (C3), atypical with disproportionately severe interstitial/tubular/vascular damage and with no/mild diabetic glomerular changes.
Results: In our study population (mean eGFR 35 mL/min/1.73 m2), typical glomerular changes (C2) of DN were observed in 22 of 23 subjects with micro- or macroalbuminuria compared with 3 of 8 subjects with normoalbuminuria (P = 0.002). By contrast, predominantly interstitial or vascular changes (C3) were seen in only 1 of 23 subjects with micro- or macroalbuminuria compared with 3 of 8 normoalbuminuric subjects (P = 0.08). Mesangial area increased progressively from normal controls to patients with type 2 diabetes and normo-, micro-, and macroalbuminuria. Varying degrees of arteriosclerosis, although not necessarily the predominant pattern, were seen in seven of eight subjects with normoalbuminuria.
Conclusions: Typical renal structural changes of DN were observed in patients with type 2 diabetes and elevated albuminuria. By contrast, in normoalbuminuric renal insufficiency, these changes were seen less frequently, likely reflecting greater contributions from aging, hypertension, and arteriosclerosis.