Your child is having a water deprivation test
The water deprivation test allows doctors to measure how concentrated your child’s urine (wee) becomes when they are not drinking. The test can take up to seven hours to complete. This page explains about the water deprivation test and what to expect when your child comes to Great Ormond Street Hospital (GOSH) to have one.
Your child needs this test to see whether they have a condition called diabetes insipidus. This is not the same as the more common condition – diabetes mellitus. Diabetes insipidus is caused either when the pituitary gland (a small gland at the base of the brain) does not release a hormone called anti diuretic hormone (ADH) or when your child’s kidneys do not react to it to control urine production.
What happens before the test?
Your child will be admitted to the ward on the day before the test is due. This is so that the doctors and nurses can prepare your child for the tests, which starts in the early morning and record your child’s fluid intake and output.
The person bringing your child to the test should have ‘Parental Responsibility’ for them. Parental Responsibility refers to the individual who has legal rights, responsibilities, duties, power and authority to make decisions for a child. If the person bringing your child does not have Parental Responsibility, we may have to cancel the test.
The doctors and nurses will explain about the test in more detail, discuss any worries you may have and ask you to sign a consent form giving permission for your child to have the test. If your child has any medical problems, particularly allergies, please tell the doctors about these. Please also bring in any medicines that your child is taking, show this to the doctor and then hand it to a nurse who will lock it away safely.
Your child will need to have a cannula (thin plastic tube) inserted into a vein so that blood samples can be taken easily. A nurse will apply some local anaesthetic cream first so that their skin in numb. If your child is over five years old, they may like to have a cold numbing spray before the needle instead of the cream.
What does the test involve?
During the day and night before the test, the nurses will measure how much fluid your child drinks and how much they urinate (wee).
From 6am on the day of the test, your child will not be able to drink anything and will only be allowed to eat dry food, such as toast or biscuits.
The nurses will take samples of your child’s blood before, during and after the test from the cannula. Each blood sample is sent to the laboratory with a urine sample collected each hour. During the test your child will need to stay on the ward so the nurses can keep a close eye on them for any side effects. The nurses will also weigh your child every hour and measure their blood pressure.
Are there any risks?
There is a very small risk that your child could become seriously dehydrated, but as they will be closely watched on the ward this is unlikely to happen. The nurses will stop the test if they are at all concerned about your child.
Your child will probably feel tired and miserable during the test because they will not be allowed to drink anything. It is important to continue the test so that we can get accurate results. However tempting it is, giving your child anything to drink will mean the test will need to be stopped and rescheduled for a later date.
While your child is not drinking, it is easy for you to forget to drink too. There is a kitchen on the ward and also the coffee shop and restaurant in the hospital so please try not to forget your own needs.
There is a risk that your child could become dehydrated when you get home, especially if they are refusing food and drink and/or vomiting (being sick).
Signs of dehydration include:
- Dry lips
- Pale skin
- Sunken eyes
- Not passing urine
What happens afterwards?
At the end of the test, some children immediately continue onto another shorter test, also with some drinking restrictions. The doctor will decide if this is necessary and discuss this with you.
How long will it take to get the results?
Your child’s test results will be given to you at your next outpatient appointment at GOSH. However, if there is a need to start on new treatment before the appointment, the hospital will contact your child’s family doctor (GP).