The insulin hypoglycemia test is also known by the synonym insulin tolerance test. The test is used to diagnose suspected disorders in the endocrine system.
What is the insulin hypoglycemia test?
The insulin hypoglycemia test is used to diagnose suspected endocrine system disorders. The insulin hypoglycemia test is a procedure used to test the regulation of the adrenocortical system via hypothalamic-pituitary control. The test belongs to the endocrinological functional tests. Often, disorders in hormone metabolism cannot be detected only by measuring hormone levels in blood or saliva. The insulin hypoglycemia test is the gold standard for checking the corticotropic axis. This is responsible for CRH–ACTH cortisol release. The somatotropic axis (growth hormone release) is also checked with the insulin hypoglycemia test. The test is used to assess pituitary function. The pituitary gland, also called the pituitary gland, plays a central role in regulating the entire hormonal system. It is located in what is known as the sella turcica, a bony depression in the cranial fossa, at about the level of the nose. The pituitary gland is divided into the anterior pituitary, the intermediate pituitary and the posterior pituitary. The anterior pituitary lobe (HVL) plays a crucial role in the insulin hypoglycemia test. It produces the hormones somatotropin, prolactin, follicle-stimulating hormone (FSH), luteinizing hormone (LH), adrenocorticotropic hormone (ACTH), and thyroid-stimulating hormone (TSH), which stimulates the thyroid gland to produce hormones.
Function, effects, and goals
The insulin hypoglycemia test is performed on the supine patient. It is important that the patient be completely fasting. Therefore, the insulin hypoglycemia test is best performed in the morning. Human Altinsulin is administered to the patient via venous access. The dosage is 0.1 IU per kilogram of body weight. In acromegaly or Cushing’s syndrome, a higher dose of 0.15 IU per kilogram of body weight may be required. A blood sample is taken before the injection. In addition, blood is drawn 15, 30, 45, 60, 90, and 120 minutes after the insulin injection. Blood draws for adrenocorticotropic hormone (ACTH) are done with EDTA monovettes or EDTA Vacutainers. Samples must be centrifuged within half an hour of collection. They are sent frozen. Cortisol and growth hormone are determined from serum. For this purpose, the serum is taken with a pipette after coagulation. After completion of the test, the patient must remain in the office for at least two hours. He is not fit to drive after this treatment. During the entire time, the patient is monitored by a physician. The doctor records pulse, blood pressure, dizziness, sweating and other symptoms in a progress log. Blood glucose levels are also documented. In parallel with the blood samples, glucose measurements are taken at five to ten minute intervals using a portable blood glucose meter. Insulin administration causes the patient’s blood glucose to drop sharply, resulting in hypoglycemia. Since cortisol and growth hormone are antagonists of insulin, the lowering of blood glucose and the rise in insulin in the blood normally results in increased secretion of cortisol and somatotropin. In a healthy adult, the growth hormone in the blood should increase by at least 3 µg/l. A growth hormone increase of less than 3 µg/l is considered evidence of a hormone deficiency. Cortisol and ACTH should reach at least one and a half to two times the original level. If the rise is absent when tested, there may be damage to the hypothalamus or pituitary gland. To see if the cause of anterior pituitary insufficiency is in the hypothalamus or pituitary, a releasing hormone test can be done. The CRH test, the GHRH test and the TRH test are suitable for this purpose. The insulin hypoglycemia test is performed when hypothalamic-related anterior pituitary insufficiency or primary anterior pituitary insufficiency (hypopituitarism) is suspected. Such insufficiency can be caused by tumors, surgical procedures on the brain, radiation therapy, injuries to the brain, or autoimmune processes.The insulin hypoglycemia test is also used for differential diagnosis in short stature and when growth hormone deficiency is suspected.
Risks, side effects, and hazards
Mild symptoms of low blood sugar (hypoglycemia) occur during the test. These are quite desirable, since hypoglycemia is, after all, deliberately induced to stimulate hormone production in the pituitary gland. Severe hypoglycemias should actually be avoided, but they can occur. They are manifested by loss of consciousness, seizures and, in the worst case, coma. To minimize the risk of severe hypoglycemia, a physician must be present during the entire test. The physician documents and monitors the glucose levels in the blood closely and, if necessary, intervenes at an early stage to counteract the hypoglycemia. For this purpose, a 20% glucose solution must be available at all times during the test for immediate injection. The insulin hypoglycemia test may not be performed on every patient. It carries some risks. Because of the risk of seizures, a cerebral seizure disorder is a contraindication to the test. Also, the insulin hypoglycemia test must not be used in cerebral circulatory disorders or in patients with coronary artery disease. Glycogen storage disorders are another contraindication. In the case of a glycogen deficiency, the body is unable to mobilize sugar despite elevated hormone levels, so there is a risk of severe hypoglycemia in this case. Newborns, infants and children under four years of age must also not be tested. Children with dystrophy and children with hypoglycemic tendencies can also develop severe hypoglycemia and metabolic acidosis very quickly during testing. In metabolic acidosis, blood pH drops below 7.36 because of increased organic acids in the body due to a metabolic disorder.
