What tests and exams led to a diagnosis of diabetes insipidus?
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How is diabetes insipidus diagnosed?
Because diabetes mellitus is more common and because diabetes mellitus and
diabetes insipidus have similar symptoms, a health care provider may suspect that a patient with
diabetes insipidus has diabetes mellitus. But testing should make the diagnosis clear.
A doctor must determine which type of diabetes insipidus is involved before proper treatment can begin. Diagnosis is based on a series of tests, including urinalysis and a fluid deprivation test.
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 or by comparing the weight of the urine with an equal volume of distilled water.
A fluid deprivation test helps determine whether diabetes insipidus is caused by one of the following:
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, a magnetic resonance imaging (MRI) of the brain may be necessary as well.