Evaluation of urinary N-acetyl-beta-D-glucosaminidase as a marker of early renal damage in patients with type 2 diabetes mellitus

Objective: To evaluate the clinical usefulness of urinary N-acetyl-beta-D-glucosaminidase (NAG) excretion for the detection of early tubular damage in type 2 diabetes mellitus (T2DM). Subjects and methods: Thirty six patients with T2DM were divided into two groups based on urinary albumin to creatinine ratio (ACR): normoalbuminuria (ACR < 30 mg/g; n = 19) and microalbuminuria (ACR = 30-300 mg/g; n = 17). The following parameters were determined in both groups: urinary NAG and albumin, serum and urine creatinine, fasting plasma glucose and glycated hemoglobin (HbA(1c)). Results: Urinary NAG levels [Units/g creatinine; median (range)] were significantly increased in microalbuminuria group [17.0 (5.9 - 23.3)] compared to normoalbuminuria group [4.4 (1.5 - 9.2)] (P < 0.001). No differences between groups were observed in fasting glucose, HbA(1c), serum creatinine levels and estimated glomerular filtration rates (eGFR). Urinary NAG positively correlated with ACR (r = 0.628; p < 0.0001), while no significant association was observed between NAG and glycemia, HbA(1c), serum creatinine and eGFR. Conclusions: The increase of urinary NAG at the microalbuminuria stage of diabetic nephropathy (DN) suggests that tubular dysfunction is already present in this period. The significant positive association between urinary NAG excretion and ACR indicates the possible clinical application of urinary NAG as a complementary marker for early detection of DN in T2DM.