You are booked to come in for a : WATER DEPRIVATION TEST
What is a water deprivation test?
Your kidneys are responsible for getting rid of body waste products dissolved in water. The amount of water lost from the kidneys (and the concentration of the urine) depend on a hormone called anti-diuretic hormone or ADH for short. A hormone is a chemical which is made in one part of the body but passes into the bloodstream and has effects on other parts of the body. ADH is made in the pituitary gland (a small gland that lies just under the brain). ADH passes into the bloodstream, is carried to the kidneys, and controls the amount of water lost in urine or reabsorbed. If the pituitary gland is not producing enough ADH, or if the kidneys lose their sensitivity to ADH, you can lose excess water from the kidneys. This makes the urine very dilute and you tend to need to pass a lot of urine. This can then result in excessive thirst. A water deprivation test looks to see if the pituitary is producing enough ADH and if your kidneys can respond to ADH.
How should I prepare for the test?
You need to stop any tobacco or alcohol for 24 hours before the test. If you are taking diuretics (water tablets) or DDAVP these must be stopped 24 hours before the test. If you are using the oral contraceptive pill or HRT, thyroxine or hydrocortisone you can continue these as normal. You do not need to fast before the test. You should drink normally and eat a light breakfast on the morning of the test.
What will happen during the test?
You should come to the ward on the date of the test, by 8:00am. You will have a bed to lie down in throughout the test. You will be weighed and a cannula (a small needle with a tube attached for taking blood samples) will be placed in a vein in your arm. The first part of the test lasts for 8 hours and investigates whether you are producing enough ADH. During that time, you will not be permitted to drink although you may be allowed some dry food provided on the ward. You will need to provide several urine specimens as directed by the nursing staff and a series of blood tests will be taken through the cannula in your arm. The second part of the test lasts for 4 hours during which you will be able to eat and drink freely. This part tests if your kidneys can respond to ADH. You will be given an injection of a form of ADH into the muscle of your arm or thigh and will be asked to provide some further urine and blood tests as directed by the nursing staff. At the end of the second part of the test you will be free to go home.
What happens after the test?
When the results of the tests are available they will be reviewed by the endocrinology team. You will be notified by letter and your GP will also be informed of the results. If there are any changes to be made to your treatment or further tests that need to be organized, these will be outlined in the letter or someone from the department may contact you by telephone.
What if I have any questions?
You will see a doctor on the day of your test who should be able to answer your queries. If you have any questions before or after your test please leave a message and contact number with the endocrine department at the Hospital where your test is booked. Someone will call you back to discuss things.