Diagnosis of reactive hypoglycemia: pitfalls in the use of the oral glucose tolerance test

The signs and symptoms of reactive hypoglycemia mimic the manifestations of other clinical disorders. The oral glucose tolerance test (OGTT) is a widely accepted diagnostic procedure to evaluate patients suspected of having reactive hypoglycemia. The reproducibility of the OGTT has not been previously assessed in a large group of patients. We evaluated the consistency of glucose nadirs at 50 mg/dl and below during two consecutive OGTTs for diagnostic screening of 59 patients with postprandial symptoms of hypoglycemia. The mean nadirs of the consecutive OGTTs were 56 +/- 12 mg and 57 +/- 13 mg, both significantly below the mean nadir of asymptomatic subjects (P less than .001). The nadir of the first OGTT was at or below 50 mg/dl in a subgroup of 20 patients ("hypoglycemic"). On the repeat OGTT, 13 previously "hypoglycemic" patients had nadirs over 50 mg/dl on the second OGTT. Nine of the 39 remaining patients had nadirs below or equal to 50 mg/dl during their second OGTT. Thus, 37% of all patients had a change in diagnostic classification in the second OGTT based on the glucose nadir level. We conclude that the glucose nadir during OGTT is an inconsistent and unreliable screening criterion for evaluating patients with recurrent postprandial hypoglycemic symptoms in clinical practice.