Water deprivation test

Used when the diagnosis of Diabetes Insipidus (DI) is in doubt.

As most cases of DI can be confirmed or excluded on history and baseline investigations, this test is generally not recommended.

This test can be potentially dangerous and is very distressing to the patient.

We suggest patients should be discussed with a paediatric endocrinologist before performing the test.

It may be more appropriate for the test to be carried out in a tertiary centre.

For this reason, a protocol for the water deprivation test is not part of this handbook.

The vast majority of children who appear to be drinking excessive amounts of fluid have “psychogenic polydipsia” (habitual drinking) and are usually able to concentrate their urine appropriately.

Many have become habitual juice drinkers and will reduce their intake if only water is offered.

Assessment of these children should be made after allowing access to water but restricting juice and other flavoured fluids.

(Children with DI will continue to drink large amounts).

• Initially check an early morning urine for osmolality following a period of only drinking water.
• Unusual features more likely to be seen in Diabetes Insipidus are:
  • drinking unusual fluids such as bath water, pets water
  • drinking through the night
  • new onset enuresis.

Urine osmolality is all that is required for initial assessment.

1. A random urine osmolality of more than 800 mosm/l will exclude Diabetes.
2. If the random urine osmolality is less than 300 mosm/L, check an early morning fasting urine osmolality.
3. Child should be allowed water only to drink the day before (no juice etc.).

If DI is still considered, please discuss with your tertiary centre.