Association between nonalbumin proteinuria and renal tubular damage of N-acetyl-β-D-glucosaminidase and its clinical relevance in patients with type 2 diabetes without albuminuria

Aim: Although albuminuria and urinary N-acetyl-β-D-glucosaminidase (uNAG) are known as progression markers of diabetic kidney disease, there is limited information regarding the association between urinary nonalbumin proteinuria (NAP) and uNAG and the clinical relevance thereof in patients without albuminuria. Methods: This cross-sectional study included samples from 244 consecutive patients with type 2 diabetes mellitus (T2D) without albuminuria. Proteinuria and albuminuria were defined according to protein-to-creatinine ratio (uPCR) and albumin-to-creatinine ratio (uACR), respectively. NAP was indirectly calculated by the difference between uPCR and uACR. Results: NAP and uNAG excretion were significantly correlated (r = 0.525, P < 0.001). Individuals whose NAP levels were in the highest tertile had a longer duration of diabetes, uncontrolled hyperglycemia, and impaired insulin stimulation (all P < 0.05), although more patients in the highest NAP tertile were prescribed insulin and sulfonylurea. Multiple linear regression analyses revealed associations among uNAG, diabetes duration, and waist circumference. Conclusions: T2D patients without albuminuria excrete proteinuria and that presence of the protein in urine is associated with uNAG. NAP was positively correlated with T2D duration and waist circumference, but negatively correlated with body mass index. Lean, but centrally obese, T2D patients in late diabetes experience more tubular damage, regardless of the presence of albuminuria.