How Is Diabetes Insipidus Diagnosed?

Diabetes insipidus is diagnosed based on a series of tests, including urinalysis and a fluid deprivation test.
A urinalysis is the physical and chemical examination of urine. The urine of a person with diabetes insipidus will be less concentrated. Therefore, the salt and waste concentrations are low and the amount of water excreted is high. A physician evaluates the concentration of urine by measuring how many particles are in a kilogram of water (osmolality) or by comparing the weight of the urine to an equal volume of distilled water (specific gravity).
A fluid deprivation test helps determine whether diabetes insipidus is caused by:
* Excessive intake of fluid
* A defect in ADH production
* A defect in the kidneys' response to ADH.
This test measures changes in body weight, urine output, and urine composition when fluids are withheld. Sometimes, measuring blood levels of ADH during this test is also necessary.
In some patients with possible diabetes insipidus symptoms, an MRI (magnetic resonance imaging) scan of the brain may be necessary as well.
Because diabetes mellitus and diabetes insipidus have similar symptoms, a healthcare provider may suspect that a patient with diabetes insipidus has diabetes mellitus. But testing should make the diagnosis clear.

August 01, 2006
Written by/reviewed by: Arthur Schoenstadt, MD
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