Insulin Tolerance Test (ITT) - Information for parents and carers

Background

In children and adults, growth hormone levels vary greatly throughout the day and night, during exercise, stress, sleep and other hormonal changes. Most of the time during the day, levels of growth hormone in the blood are very low and difficult to measure. This means it is necessary to stimulate the release of growth hormone, to accurately assess how much your child is able to produce.

Preparation for the test

If your child is on any hormone replacement medicines, for example, hydrocortisone or levothyroxine, these should be omitted on the day of the test but you should bring them with you so that they can be given at the end. If your child is already receiving growth hormone therapy, this must be stopped four weeks prior to the test.

Your child should not eat anything from midnight (unless specified otherwise) before the test, but they can drink water if thirsty.

On the day of the test

On arrival, the doctor will discuss the test with you and give you the opportunity to ask questions. You will need to sign a consent form on behalf of your child if they are under 16 years of age. At the start of the procedure, we will insert an intra-venous cannula (small plastic tube) into the crook of your child’s arm, or the back of their hand. The topical anaesthetic cream you have been given will help to numb the area. Your child will then be given a very small dose of insulin. This indirectly stimulates their body to release growth hormone. The amount of growth hormone your child produces will be measured by taking regular small blood samples via the cannula throughout the test which will last approximately two hours. Your child will not be able to eat during the test, but can drink water if they feel thirsty. As soon as the test is finished, they can eat and drink again normally. At the end of the test, the cannula will be removed. Your child will then be discharged home, usually later the same day.

Effects of insulin

The most common effect of an ITT test is having low levels of sugar in the blood. This can cause drowsiness, hunger, shaking and sweatiness. Very rarely, a child may lose consciousness or have fits. The effects are quickly reversed by giving a sweet sugary drink and/ or intravenous dextrose. Your child will be closely monitored throughout the test by an experienced doctor and nurse and only be allowed home when their blood sugar levels are back to normal.

Follow-up

At your follow-up appointment you will have the opportunity to discuss the blood results with the doctor and whether any further treatment or tests are necessary.

Contacts

Please do ask the doctors any questions you may have or contact the Specialist Endocrine Nurses on 01223 217496.