Efficacy of insulin and C-peptide suppression test using a rapid-acting insulin analog to induce hypoglycemia in the diagnosis of insulinoma: A comparison to the supervised prolonged fast test

The efficacy of insulin and C-peptide suppression (ICPS) test using a rapid-acting insulin analog to induce hypoglycemia in the diagnosis of insulinoma has never been studied. To compare the efficacy of using plasma C-peptide (PCP) and plasma insulin (PI) responses to the ICPS test using insulin aspart and the supervised prolonged fast (SPF) test in the diagnosis of insulinoma. The ICPS test was performed in 15 patients with insulinoma (IN) and 6 patients with non-insulinoma causes of hypoglycemia (non-IN) by intravenous infusion of insulin aspart to induce hypoglycemia. Plasma glucose (PG), C-peptide (PCP), and insulin (PI) levels were measured before and at the end of the test (end-ICPS) when the patients had hypoglycemia, defined by the presence of either PG ≤50 mg/dL with hypoglycemic symptoms or PG ≤40 mg/dL regardless of hypoglycemic symptoms. PCP and PI were measured by an immunoassay system that does not cross-react to insulin aspart (Cobas Modular Analytics e801). The SPF test was also performed in IN. IN had a higher median end-ICPS PI (34.77 versus 0.58 μIU/mL, p