Urinary Enzyme Levels Correlate with Prediabetic Plasma Glucose

Urinary N-acetyl-β-D-glucosaminidase (NAG) excretion is increased in patients with impaired glucose tolerance (IGT).

During the oral glucose tolerance test (OGTT) the plasma glucose, urine glucose, and insulin levels correlate strongly with urinary N-acetyl-β-d-glucosaminidase (NAG) levels in prediabetic subjects.

Scientists at the Nippon Medical School (Tokyo, Japan) performed OGTTs on 33 men and 47 women, aged 18 to79 years, who were not yet diagnosed with diabetes mellitus (DM), and in whom HbA1c levels were equal to or greater than 6.8%. The study was carried out from December 2005 through August 2010.

Urinary NAG levels were measured spectrophotometrically with sodio- metacresolsulfonphthaleinyl- N-acetyl-β-D-glucosaminide as a substrate (NAG assay kit, Shionogi & Co., Osaka, Japan). Urinary glucose levels and serum creatinine (Cr) levels were measured with enzymatic assays. The serum levels of cystatin C were measured with the N Latex Cystatin C kit (Siemens Healthcare Diagnostics, Inc., Marburg, Germany) and the fully automated particle-enhanced nephelometric immunoassay.

Forty-two subjects had normal glucose tolerance (NGT), 31 had impaired glucose tolerance (IGT), and seven had DM. NAG levels were significantly higher in subjects with DM and in subjects with IGT than in subjects with NGT. Urinary NAG in the DM group was 8.53 ± 4.96 U/g UCr, which was elevated compared to the NGT group, which ranged from 5.40 ± 3.82 U/g UCr. The IGT group's range was 6.60 ± 2.88 U/g UCr, which was also significantly higher than the nondiabetic group. The NAG level was positively correlated with plasma glucose levels at 120 minutes of the OGTT and was associated with the glycemic status of prediabetic patients.

The authors concluded that that the urinary excretion of NAG with other urinary enzymes in the prediabetic state is an appropriate biomarker for screening for prediabetic renal dysfunction. Their results suggest that postprandial hyperglycemia is an independent factor that causes renal tubular damage in prediabetes patients. The study was published on November 9, 2012, in the Journal of Clinical Laboratory Analysis.

Related Links:
Nippon Medical School
Shionogi & Co.
Siemens Healthcare Diagnostics