MILLER WATER DEPRIVATION TEST

Your endocrinologist has requested a special investigation to determine whether you are able to produce concentrated urine when deprived of fluid. People with symptoms of thirst and an increase in urine production may have a condition where the main hormone which limits urine output is deficient or not working. This hormone is known by 2 names: arginine vasopressin (AVP) or antidiuretic hormone (ADH). A condition called diabetes insipidus may result from absent levels of AVP or a problem whereby the kidney does not respond to normal or high levels of AVP.

Procedure

The aim is to stop you from drinking any fluid for a period of time to see if the urine concentrates. The length of time without fluid depends on how severe the excessive urine output is and will be decided on based on urine concentration and amount of weight loss. At 6.00am on the morning of the test you will be weighed and pass urine. A blood test will be done at 8.00am. Every hour you will be asked to pass urine to check its concentration, and will be weighed. This will continue until the urine concentration is the same over 2 hours or you lose greater than 3% of your body weight. At that point another blood test will be drawn and a nasal spray of synthetic DDAVP (a longer acting version of AVP) given into each nostril. People with a deficiency of AVP will then concentrate their urine, while those with the kidney problem will not. A further blood and urine sample is taken 1 hour after the nasal spray. At this point you will be allowed to drink again.

Risks

This test is very safe and you will be closely monitored to ensure you do not become too dehydrated. You may become profoundly thirsty. Generally, people with a more severe problem do not need a long period of water deprivation to produce a clear cut result. Milder conditions may require a number of hours.