Children and Young People’s Endocrine Team
Your child has been asked to come for a ‘pituitary function test’
This is part of the investigations into your child’s poor growth pattern.
The purpose of the test is to assess the function of a small but important gland found deep inside the brain called the ‘pituitary gland’. It produces special ‘messenger’ hormones which ‘tell’ other glands in the body to make specific hormones which, in turn, influence the way the body works, grows and develops.
One of the hormones it produces is growth hormone.
The test will measure the amount of growth hormone your child is producing along with some of the other pituitary hormones associated with growth and development.
Paediatric decisions unit (PDU)
You have been asked to come to the PDU. This is situated in the maternity entrance to the hospital, upstairs and along the corridor next to ward 21.
Please note that there is a parking charge, and parking can occasionally be a problem, so please allow sufficient time before your appointment to find a parking space.
Do not let your child eat or drink anything except plain water from 12 midnight on the evening prior to the test.
When you arrive
Your child will be weighed and measured and we will check your details. The nurse performing the procedure will go over it again with you and will try to answer any questions that you may have at this point.
We will ask you to sign a consent form for the procedure so please ensure that your child is accompanied by their legal guardian.
The test involves inserting a cannula into one of your child’s veins.
This is a very small plastic tube with a needle through the inside, the needle pierces the vein and is then removed leaving the hollow plastic tube in the vein – usually on the back of the hand or inside the elbow.
Before the cannula is inserted, we usually apply some local anaesthetic cream to the area over the vein; this takes 45 to 60 minutes to work. You might have been given some of this cream at your clinic appointment prior to the test being arranged for you to apply before you come in on the day of the test.
Alternatively your child may prefer cryogesic spray which freezes the area and works immediately on application. We will ask which they prefer when you arrive.
Once the cannula is in, a sample of blood will be taken from it to measure baseline levels of growth hormone and other hormones associated with growth and development. Any other blood tests the doctor has requested will be taken at this point.
After half an hour an injection of a messenger hormone called glucagon will be prescribed and given into the mid-thigh muscle which will stimulate production of growth hormone. It needs to be slower acting which is why it is given into the muscle rather than the vein.
If the doctor has requested, we may also prescribe measured doses of other releasing hormones to be given through the cannula at this point. These will tell the pituitary gland to produce other messenger hormones so that we can measure what the pituitary gland is making.
We will continue to take blood samples from the cannula every 30 minutes for the next three to four hours in order to assess the amounts of growth hormone your child has produced in response to the stimulation to the Pituitary Gland.
Why does the test take up to four and a half hours?
Growth hormone is not produced in constant amounts. It is made in pulses throughout the day and more so at night time.
As well as growth of the bones and general repair of the body’s cells, one of the other major things that growth hormone does is to help convert sugar stored in the liver into energy.
With adequate stimulation and the right body conditions, for example; a state of starvation, the body should be able to produce a good peak amount of growth hormone in order to try and regulate the blood sugar. We will be able to measure the maximum amount of hormone it can produce over a period of time.
Your child will only be allowed plain water to drink for the duration of the test.
The test will make your child become hypoglycaemic (low blood glucose level), but the nurse will observe them closely and will measure their blood glucose on a blood glucose meter every time a blood sample is obtained.
If the level of blood sugar drops too low (for example; below 2.5mmol/l), your child will be given a sugary drink. We will continue with the test and retest the glucose level after 15min.
If the glucose levels have not responded to this, then we will give him or her some glucose through the cannula straight into the vein. At this point we may also need to give some hydrocortisone, a steroid hormone which will help to regulate the blood glucose level. We would stop the test if this happens.
After the test
Once the test is completed – usually at around 14:00 hours (depending on when it was started) your child will be allowed something to eat and drink.
We can order some lunch for your child from the ward kitchen. The hostess will inform you of the menu so that your child can choose what they would like to eat once the last blood sample has been obtained. Their meal will be brought to them.
We can provide toast or cereal if they prefer.
You are welcome to bring your child’s favourite food in with you – which is especially useful if he or she is a picky eater because they must have eaten a substantial meal before you are allowed home.
Once they have eaten, we will check your child’s blood glucose level to ensure it within normal range before removing the cannula. You will be allowed home after a short period of observation.
We may send your child for an x-ray of their left hand before you go home. This is to check that the bones are growing at the correct rate for their age (sometimes the bones can grow at a slower rate, which can be a feature of short stature). The x-ray will be assessed by a specialist and we will not get the results immediately, so there is no need for you to return to the ward once it has been done
When you get home
There is a risk that the blood glucose level can drop suddenly in the few hours following the test, once you get home. This is called rebound hypoglycaemia.
We recommend that you give your child small frequent amounts of sugary or starchy food and drink to help prevent this from occurring.
Examples of signs to watch out for are:
Drowsiness and difficult to rouse
Sweaty and clammy skin
Irritability and tearful or may appear confused
Drowsiness and difficult to rouse
Nausea or vomiting
Feeling very hungry
If you are worried that your child has any of these symptoms please given them sugary food or drink, for example coke, lemonade or fresh fruit juice, Haribo sweets (or something similar) followed by something starchy to eat for example; a digestive biscuit, crisps, piece of toast or cereal.
If there is no improvement after 10-15 minutes repeat the sugary and starchy food or drink.
If you are concerned that your child’s condition is not improving please contact the paediatric decisons unit (PDU) on 01642 854896.
The results will be sent to the Consultant in charge of your child’s care. They normally take up to two weeks to come back.
Once we have the results, you will be given the opportunity to discuss them with the consultant at your next clinic appointment. If you wish to know the results before you see the consultant, please contact their secretary – but please be assured that if they are abnormal we would contact you.
South Tees Hospitals NHS Foundation Trust would like your feedback. If you wish to share your experience about your care and treatment or on behalf of a patient, please contact The Patient Experience Department who will advise you on how best to do this.
This service is based at The James Cook University Hospital but also covers the Friarage Hospital in Northallerton, our community hospitals and community health services.