Evidence for Elevated Glucose Threshold in Patients With Impaired Glucose Tolerance and Symptoms of Hypoglycemia During OGTT

We evaluated the relationship between hypoglycemic symptoms, glucose nadir levels, and hormone changes in patients with impaired glucose tolerance (IGT) after an oral glucose tolerance test (OGTT). The peak counterregulatory hormone response was determined at the glucose nadir identified by continuous glucose monitoring. Eight patients with IGT who had symptoms and signs typical of hypoglycemia at the glucose nadir were compared with completely asymptomatic subjects (5 IGT patients and 13 patients who had normal glucose tolerance [NGT]). The mean glucose nadir of symptomatic IGT patients was 3.50 ± 0.46 mM, which was not statistically different from the mean of asymptomatic NGT patients (4.10 ± 0.56 mM) but was significantly lower than that for asymptomatic IGT patients (5.10 ± 0.81 mM, P < 0.001). Seven of 8 symptomatic IGT patients had glucose levels that never fell below the range of glucose nadirs for asymptomatic NGT patients. However, the symptomatic IGT group had significantly higher levels of growth hormone, cortisol, epinephrine, and norepinephrine than the asymptomatic groups in response to the nadir. We conclude that patients with IGT are capable of experiencing signs and symptoms of hypoglycemia at physiological glucose levels during OGTT with reflex stimulation of counterregulatory hormone release. This may indicate that symptomatic IGT patients have a higher glucose threshold for eliciting characteristic hypoglycemic symptom episodes than individuals with NGT.