Why is it done?
The Insulin Tolerance Test is done to evaluate patients who are suspected of having adrenal or growth hormone (GH) deficiencies. Adrenal insufficiency is a disorder in which the adrenal glands don't produce enough hormone called cortisol, which has an important function in the regulation of blood glucose, blood pressure, and overall wellbeing. A decrease in adrenal function may be related to a problem with the adrenal glands or a disorder affecting the pituitary gland, which is a small pea size gland below the brain. Growth hormone deficiency is usually caused by a disease affecting the pituitary gland. Patients with GH deficiency may have increased body fat, decreased muscle mass, low bone density, and reduced quality of life.
Precaution:
The test is not done in those above 65 years old, or those with heart diseases, seizures, or stroke.
Preparation:
The endocrine nurse will review all your medicines, vitamins, and supplements with you. Some drugs can affect the test and need to be stopped prior to the test. Patients who have been on GH therapy, need to be off GH for at least 30 days before the test. Patients taking hydrocortisone or prednisone for adrenal insufficiency need to hold their medications for 24 hours before the test (last dose in the morning the day before the test). The test needs to be done fasting in the morning. You should not take any food or drinks except water after midnight.
How long is the test?
The test takes about 3 hours. This includes registration, placing an IV, testing, and discharge.
Procedure:
The test is done lying down in a recliner. An endocrine nurse remains with you during the testing. After lying flat an IV is placed in a vein in your arm or hand. After the IV is placed, the needle is removed, and a small, flexible catheter remains. An IV is used, so you don’t have to get multiple needle sticks.
After the initial blood draw, the endocrine nurse will give you an injection of insulin through your IV to lower your blood glucose level. Following the injection of insulin, blood samples will be drawn at 15, 30, 45 and 60 minutes.
In about 10-20% of patients, a second dose of insulin may be necessary. At the end of the procedure, the nurse will give you a light snack with juice, making sure your blood glucose level is back to normal. During the test, patients experience symptoms of hypoglycemia (low blood glucose level). In healthy subjects, hypoglycemia results in an elevation of cortisol and GH levels. Patients with adrenal insufficiency and GH deficiency cannot raise their cortisol and GH levels, respectively.
Possible side-effects:
When your blood glucose drops, you will have one or more symptoms of hypoglycemia including sweating, rapid heart rate, headache, shakiness, and lightheadedness. The endocrine nurse will closely monitor you during the test. An intravenous injection of glucose will be given to you to rapidly increase your blood glucose level in the event of any severe symptoms.
Other side-effects are related to the IV and include:
- Bleeding from IV insertion site
- Bruising
- Infection- rare as the sterile technique is used
- Hematoma-blood under the skin
- Multiple punctures to locate veins
Results:
Results are available in a week. Please contact your doctor if you are not called about the result.