A syndrome with excessively high INSULIN levels in the BLOOD. It may cause HYPOGLYCEMIA. Etiology of hyperinsulinism varies, including hypersecretion of a beta cell tumor (INSULINOMA); autoantibodies against insulin (INSULIN ANTIBODIES); defective insulin receptor (INSULIN RESISTANCE); or overuse of exogenous insulin or HYPOGLYCEMIC AGENTS. | A GLUCOSE-induced HYPERINSULINEMIA, a marker of insulin-resistant state. It is a mechanism to compensate for reduced sensitivity to insulin. [MeSH]