A water deprivation test checks how the body responds to several hours without water intake. A doctor may request this test to help diagnose conditions such as arginine vasopressin disorder (AVD).

Arginine vasopressin disorder (AVD), formerly known as diabetes insipidus, typically causes a person to pass high volumes of diluted urine. It often occurs due to an individual producing low levels of vasopressin or not responding enough to the hormone.

This hormone is responsible for water balance and controlling urine concentration. Problems with this hormone can lead to excessive urination, dehydration, and electrolyte imbalance.

Diagnosing AVD involves several tests, including blood and urine tests, MRI scans, and tests to measure the body’s response to vasopressin. One of these tests, the water deprivation test, plays a key role in identifying AVD and its possible causes.

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Some doctors refer to a water deprivation test as an indirect water deprivation test or dehydration test. During a water deprivation test, a person must not consume water for a fixed time.

People with AVD will continue to produce a high volume of urine, but it will not contain many concentrates, which are waste products the body usually removes via urine. Those who do not have AVD will produce smaller amounts of urine that are more concentrated.

The water deprivation test can help a doctor identify AVD. It may also determine the type of the condition. The different types of AVD the water deprivation test can help distinguish between include:

  • Arginine vasopressin disorder (AVP-D): The pituitary gland usually releases vasopressin, but in people with AVP-D, it does not produce enough due to injury, cancer, immune overactivity, or other disorders.
  • Arginine vasopressin resistance (AVP-R): This refers to receptors in the kidneys that lose sensitivity to vasopressin.
  • Primary polydipsia: This type occurs due to problems with the hypothalamus, causing a person to experience extreme thirst.

A doctor almost always gives a small dose of artificial vasopressin, known as desmopressin, after the water deprivation test. This can also help them distinguish between the different types of AVD.

A person needs to take several steps 24 hours before the test to prepare for the water deprivation test. These include:

  • stopping medications that affect how much urine a person makes, such as desmopressin, diuretics, carbamazepine, chlorpropamide, glucocorticoids, nonsteroidal anti-inflammatory drugs (NSAIDs), and sodium-glucose cotransporter-2 inhibitors
  • avoiding smoking, if applicable
  • stopping caffeine intake

Bringing another person to the appointment can help in case adverse effects occur. Until the test starts, an individual needs to continue drinking water as they typically do.

The test’s main method involves cutting out water and fluid intake. If excess urine production is mild, the doctor may recommend overnight water deprivation with testing in the morning. However, those with severe excess urine or who pass urine in the night may benefit from a daytime test under physician supervision.

Doctors use body weight and urine output to determine the length of time someone needs to avoid water during the dehydration phase. A person taking a water deprivation test may not consume any fluids or food for the duration.

The individual will pass urine before the test starts, and the doctor will measure weight, blood pressure, and heart rate hourly to monitor well-being. Doctors measure urine output and carry out blood tests every 2 hours.

A “desmopressin phase” follows most water deprivation tests. A doctor injects an artificial form of vasopressin and checks the urine and blood hourly for the next 1 to 2 hours. The individual can eat and drink during this part of the test.

The test should take under 8 hours for people with total AVD, though it may take longer if a doctor suspects other health problems.

When interpreting the results of a water deprivation test, a doctor will look at the osmolarity of urine and blood during the test period. The term osmolarity refers to the concentration of particles in the urine and blood. The healthcare professional will also see how administering desmopressin influenced urine osmolarity.

For example, typical values of the test are as follows:

AVP-DAVP-RPrimary polydipsia
Serum osmolarity (milliosmoles of the solutes per kilogram mOsm/Kg)>300>300<295
Urine osmolarity (mOsm/Kg)<300<300>600
Post desmopressin urine osmolarity (mOsm/Kg)>400 to 600No responseNo or mild response

Read on to learn more about AVD and urine osmolarity.

Water deprivation test involves deliberate dehydration, which can lead to the following side effects:

  • nausea
  • dizziness
  • diarrhea
  • fainting
  • extreme thirst

For safety reasons, the doctor will end the test if any of these adverse effects occur. If these effects occur on a test during which deprivation takes place at home, the medical team will start the test again as an in-hospital procedure. They can more readily monitor adverse effects this way.

The water deprivation test involves someone abstaining from water for a set time to see how it influences their urine. A healthcare professional may request this test to help diagnose AVD and differentiate between types.

A doctor will ask people to stop taking any medication that affects urine output, consuming caffeine, and smoking before the test. People will usually have to avoid drinking water for 8 hours or longer, depending on the type. A doctor takes measurements throughout. Adverse effects may include nausea, dizziness, fainting, and extreme thirst.