Elevated Hypoglycemic Index and Late Hyperinsulinism in Symptomatic Postprandial Hypoglycemia*

Abstract

We monitored the blood glucose continuously (CGM) during an oral glucose tolerance test in 28 subjects referred for symptoms compatible with postprandial hypoglycemia. In addition, intermittent blood samples were collected every 30 min for glucose and insulin determinations. The patients were classified into 3 groups based on their glucose tolerance and the manifestation during the oral glucose tolerance test of symptoms associated with a glucose nadir of less than 60 mg/dl (CGM). Group 1 (n=16) consisted of asymptomatic subjects with normal glucose tolerance. Patients in groups 2 (n=4) and 3 (n=8) had symptomatic hypoglycemia and exhibited impaired and normal glucose tolerance, respectively. We assessed the use of the glucose nadir as the only diagnostic criterion for symptomatic postprandial hypoglycemia. A value below 50 mg/dl would have resulted in no false positives; however, the diagnosis would have been missed in two out of three of the symptomatic patients. Although a glucose nadir above 60 mg/dl (CGM) or 65 mg/dl (intermittent samples) can exclude the diagnosis, 44% of the asymptomatic patients had glucose nadirs between 50-60 mg/dl (CGM) or 50–65 mg/dl (intermittent). The hypoglycemic index (defined as the fall in blood glucose during a 90-min period before reaching the nadir, divided by the value of the glucose nadir) provided a better diagnostic criterion for symptomatic hypoglycemia than did the glucose nadir alone. All symptomatic and none of the asymptomatic patients had an elevated hypoglycemic index. High insulin levels 90 min before the lowest blood glucose levels were common in both symptomatic groups and correlated significantly with the hypoglycemic index. We conclude that postprandial hypoglycemia can be diagnosed accurately with the combined use of the glucose nadir and the hypoglycemic index. The latter can effectively diagnose patients with glucose nadirs in the equivocal range of 50–65 mg/dl (intermittent). An elevated hypoglycemic index is associated with symptoms and reflects late hyperinsulinism.