Insulin stress test (insulin tolerance test)

Your doctor has recommended that you take this test to help with the diagnosis and the management of your condition. Please would you read this carefully and ask us about anything that is not clear or if you would like more information.

This test will tell us if your pituitary gland (at the base of the brain) is producing sufficient growth hormone, and/or properly regulating your production of cortisol (a natural steroid hormone or chemical signal).

In children, growth hormone is important for growth! In young adults, it is important for the maturation of bones and muscles. In older adults, a lack of growth hormone sometimes affects quality of life or mood. NICE (the National Institute of Clinical Excellence) have issued guidelines about GH treatment in all age groups, and specified that it should only be given to patients who meet certain criteria.

Cortisol is produced by the adrenal glands, which are just above the kidneys, in response to instructions from the pituitary gland, which is a small gland beneath the brain. A problem with either of these glands can result in low cortisol levels. Cortisol has many vital roles in maintaining normal healthy functioning, and is a very important part of the response to ‘stress’ of any kind, including other illnesses.

The test will take a full morning. After lunch you will be free to go home. We advise you not to drive until two hours after the test has finished.

The test will be carried out by an endocrine specialist nurse and a doctor.

Please have nothing to eat or drink except water for 10 hours before the test. You should have a discussion with your endocrinologist or endocrine specialist nurse before the test, who will advise you about whether or not to take your regular tablets and medicines on the morning of the test.

You will be given an injection of insulin. This is a natural hormone used to treat patients with diabetes. In this test insulin is used to make your blood sugar levels fall lower than normal for a short time. This is a stress for your body and should stimulate a growth hormone and cortisol response.

We will weigh you so that we can work out the correct dose of insulin for you. You will have (or have had previously) an ECG (heart tracing) to check that this is normal. The doctor or nurse will use a needle to insert a small plastic tube into a vein in your arm. We will use this to take blood samples and to give you the injections. After we have taken the first blood samples, we will give you the injection of insulin. We measure your response to the test through blood samples that we will take over the next two hours.