Final answer:
To rule out an insulinoma, a glucagon tolerance test can be used. The test helps to discern if hypoglycemia is due to excessive insulin production by an insulinoma or the presence of insulin antagonists, which maintains glucose levels despite the administration of glucagon.
Step-by-step explanation:
To rule out an insulinoma in patients who surreptitiously use excess sulfonylureas, a glucagon tolerance test can be administered. If hyperglycemia is observed after the administration of glucagon, it indicates that diabetes is due to defective insulin receptors. On the other hand, in the presence of excessive insulin antagonists like glucagons, growth hormone, epinephrine, glucocorticoids, or testosterone, there may be no significant change in blood glucose levels. This is because these insulin antagonists prevent the action of insulin, hence maintaining the levels of glucose despite the administration of glucagon.
Insulinomas, which are tumors of the β-cells of the pancreas, lead to an overproduction of insulin and thus cause hypoglycemia. Signs of hypoglycemia include sweating, tremors, fainting attacks, and can be relieved by injecting glucose or by oral intake of sugar. Therefore, if a glucagon tolerance test does not significantly increase blood glucose levels, it may suggest that the patient's signs of hypoglycemia are due to an insulinoma rather than an excess of insulin antagonists.