How to Prepare for a Water Deprivation Test

If you are suddenly experiencing excessive urination (polyuria), your doctor may suspect you have an endocrine disorder called diabetes insipidus. Diabetes insipidus occurs when the body is not producing enough anti-diuretic hormone (ADH) and cannot retain water, thus leading to polyuria. The most reliable way to diagnose diabetes insipidus is through a water deprivation test.

What is a water deprivation test?

A water deprivation test is designed to see how concentrated your urine and blood are in the absence of water for several hours and what the cause is. During the exam, a doctor will inject you with ADH and then monitor your blood and urine output every hour. The collected samples are then tested for specific gravity and osmololity (or concentration.) If the urine osmololity increases, this would indicate troubles with water retention in the kidneys. If urine osmololity decreases, the cause of the problem is in the pituitary gland.

What can I expect the day of my water deprivation test?

Your doctor will advise you to not eat, drink, or smoke after midnight on the morning of the exam. Once you arrive for the exam, you will be weighed and have your blood and urine checked for baseline data. You will then receive an injection of ADH (or vasopressin.) Each hour, urine and blood samples will be taken and checked for osmololity. Your weight and postural blood pressure will also be checked hourly. The exam can take up to eight hours to complete.

How do I prepare for my water deprivation test?

Because your body will be at risk for a state of dehydration, make sure you eat well balanced meals and drink plenty of fluids before fasting for the exam. Also, inform your doctor of any and all medications you take on a regular basis. Some drugs may interfere with test results and you may be required to withhold these medication for up to 48 hours before beginning your water deprivation test. Although the test may take up to 8 hours to complete, it may be terminated sooner if early lab results yield a diagnosis or if the patient has lost too much weight (up to 3% of their body weight.) Because of the length of the test, it may be a wise idea to bring a book or MP3 player to pass the time.

Note: this article is for information purposes only. If your doctor has ordered a water deprivation test for you, follow his or her instructions on how to prepare.

Sources:

Merck, Central Diabetes Insipidus (2007). Retrieved on November 30, 2010

LeMone, Priscilla & Burke, Karen (2008). Medical-Surgical Nursing-Critical Thinking In Client Care (4 ^th ed.). Upper Saddle River NJ: Pearson Prentice Hall p. 523