Plasma 1,5-anhydroglucitol concentrations are influenced by variations in the renal threshold for glucose

Aims Measurement of serum 1,5-anhydroglucitol (1,5AG) concentrations has been proposed as an alternative to HbA(1c) as both a marker of diabetic glycaemic control and as a screening rest for diabetes. The sugar competes with glucose for renal tubular reabsorption, so hyperglycaemia leads to reduced serum 1,5AG concentrations through increased urinary loss. This study has sought to establish whether plasma 1,5AG can be influenced by nut only hyperglycaemia, but by variations in renal threshold fur glucose. Methods Thirty-eight pregnant women (median age 30 years, range 20-43) found to be normoglycaemic after a 75-g carbohydrate load had plasma 1,5AG and urine glucose measured. Results Using multivariate analysis, the presence and degree of detectable glycosuria at 2h post glucose load was strongly predictive of a low plasma 1,5AG concentration (P=0.0012) independently of lasting plasma glucose (P=0.96), 2h glucose (P=0.029), subject age (P=0.97) and gestation (P=0.36). Thus, when matched fur plasma glucose areas under the glucose load curve, 16 glycosuric subjects had significantly lower 1,5AG concentrations compared to 16 nonglycosuric ones (median 1,SAG 46 mu mol/l (IQR 30-56) vs. 72 mu mol/l (IQR 55-79, P=0.017). Conclusions People with the same glucose tolerance may demonstrate variable plasma 1,5AG concentrations depending on their renal threshold for glucose. This inherent characteristic is likely to limit the usefulness of the test when monitoring or screening for diabetes.