Central Diabetes Insipidus
Because diabetes mellitus is more common, and because diabetes mellitus and central diabetes insipidus have similar symptoms, a healthcare provider may suspect that a patient with central diabetes insipidus has diabetes mellitus; however, testing should make the diagnosis clear.
A central diabetes insipidus diagnosis is based on a series of tests, including a fluid deprivation test and urinalysis.
Fluid Deprivation Test
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 central diabetes insipidus symptoms, an MRI (magnetic resonance imaging) scan of the brain may be necessary as well.
Urinalysis is the physical and chemical examination of urine. The urine of a person with central 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 specialist should determine which form of diabetes insipidus is present before starting any diabetes insipidus treatment. If central diabetes insipidus is diagnosed, the patient will be treated with a synthetic hormone called desmopressin. Desmopressin can be taken through an injection, a nasal spray, or a pill.
While taking desmopressin for central diabetes insipidus, you should drink water or other fluids only when you are thirsty and not at other times. This is because the drug prevents water excretion and water can build up now that your kidneys are making less urine and are less responsive to changes in body fluids.