Mini-fasting tests diagnosing endogenous hyperinsulinism: a follow-up of 26 cases.

CONTEXT: The supervised 72-h fast remains the gold standard test for the diagnosis of endogenous hyperinsulinism and has recently been suggested to be shortened or even avoided. OBJECTIVE: This study aimed to evaluate whether measurement of blood glucose, insulin and C-peptide levels after a 12 h overnight fast (mini-fasting test), in at least 3 consecutive days, could allow making or ruling out diagnosis of endogenous hyperinsulinism, according to the Endocrine Society's recent guidelines. PATIENTS AND METHODS: We performed 12 h mini-fasting test in at least 3 consecutive days, dosing blood glucose, insulin and C-peptide levels in 26 inpatient patients with pathologically proven endogenous hyperinsulinism. RESULTS: In our series, 100% of patients showed insulin levels of at least 3 µU/ml and C-peptide levels of at least 0.6 ng/ml concomitant with symptomatic hypoglycemia (≤ 55 mg/dl). CONCLUSION: It leads to the conclusion that mini-fasting test might avoid, in most cases, prolonged fasting test for the diagnosis of hypoglycemia due to endogenous hyperinsulinism.

Glucagon test in insulinoma: Is it useful?

Diagnosis of endogenous hyperinsulinism caused by insulinoma is based on confirmation of hypoglycemia during the symptoms associated to elevated insulin levels. Patients with insulinoma may demonstrate an excessive insulin response and subsequent hypoglycemia after 1 mg of glucagon iv injection. Glucagon test was performed in 11 patients with insulinoma before therapy and in 4 after therapy. Our study suggests that the presence of plasma glucose levels less than 55 mg/dl and below baseline at time 120 min of glucagon test strongly reinforce the diagnosis of insulinoma.