The effects of hyperglycaemia on isotopic measurement of glucose utilisation using [23H], [33H] and [614C] glucose in patients with Type 1 (insulin-dependent) diabetes mellitus

To determine whether hyperglycaemia alters the accuracy with which [23H] and [33H]glucose reflect glucose turnover measured with [614C]glucose in patients with Type 1 (insulin-dependent) diabetes mellitus, glucose utilisation rates were measured during a simultaneous infusion of [23H], [33H] and [614C]glucose after maintenance of normoglycaemia overnight and when glucose concentrations were clamped at 5.3, 7.5 and 9.7 mmol/l while insulin and glucagon concentrations were held constant. Glucose utilisation rates determined with all three isotopes were comparable in the diabetic patients at all glucose concentrations studied. On the other hand, glucose utilisation rates in nondiabetic subjects determined with [614C]glucose were greater (p<0.01) than those determined with [33H]glucose and lower (p<0.04) than those determined with [23H]glucose during the 5.3, 7.5 and 9.7 mmol/l clamps. Nevertheless, glucose utilisation rates in the diabetic patients were lower (p<0.05) than those in the nondiabetic subjects for each glucose isotope. We conclude that hyperglycaemia does not alter the pattern of metabolism of [23H] or [33H]glucose in patients with Type 1 (insulin-dependent) diabetes mellitus.