Urinary N-Acetyl-β-Glucosaminidase Activity in Type I Diabetes Mellitus

A commercial method for N-acetyl-β-glucosaminidase (NAG) is described for use on a discrete analyser. Timed overnight urine was obtained from 20 healthy volunteers and 60 Type I diabetic patients for estimation of NAG (expressed in relation to creatinine) and albumin excretion rate (AER). The upper reference limit for NAG excretion in the control patients was found to be 0·25 U/mmol creatinine but was abnormally raised in 60% of Type I diabetic patients before any increase in AER (greater than 20 μg/min), and in 82% of patients with AER greater than 200 μg/min. A positive correlation was found between NAG excretion and AER in Type I diabetes ( r = 0·61, p < 0·01), but not with glycaemic control as measured by serum fructosamine levels. We conclude that measurement of NAG excretion in diabetes indicates renal tubular dysfunction or damage before any significant change in albumin excretion rate.