Diagnosing Nephrogenic Diabetes Insipidus
Because
diabetes mellitus is more common and because diabetes mellitus and nephrogenic
diabetes insipidus have similar symptoms, a healthcare provider may suspect that a patient with nephrogenic diabetes insipidus has diabetes mellitus. But testing should make the diagnosis clear.
A nephrogenic diabetes insipidus diagnosis is based on a series of tests, including urinalysis and a fluid deprivation test.
Urinalysis
Urinalysis is the physical and chemical examination of urine. The urine of a person with nephrogenic 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).
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.
Nephrogenic Diabetes Insipidus Treatment
A specialist should determine which form of diabetes insipidus is present before starting any
diabetes insipidus treatment. If a diagnosis of nephrogenic diabetes insipidus is confirmed, the patient may be given a drug called
hydrochlorothiazide (also called
HCTZ) or
indomethacin. HCTZ is sometimes combined with another drug called
amiloride. The combination of HCTZ and amiloride is sold under the brand name
Moduretic®. With this combination of drugs, you should drink fluids only when you are thirsty and not at other times.
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