Adipsia Workup

Updated: Dec 30, 2014
  • Author: Vikas R Dharnidharka, MD, MPH; Chief Editor: Craig B Langman, MD  more...
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Workup

Laboratory Studies

The following studies are indicated in patients with adipsia:

  • Serum electrolytes, BUN, and serum creatinine levels

    • Suspicion of adipsia frequently results from serum electrolyte abnormalities.

    • Hypernatremia is a hallmark of clinically significant water deficit that may be due to adipsia.

    • Volume depletion that is associated with adipsia also causes elevations in BUN and creatinine levels and an increase in the BUN/creatinine ratio.

  • Serum osmolality: The water deficit results in a markedly elevated serum osmolality.

  • Urine electrolyte levels and osmolality

    • Simultaneous measurements of urine electrolytes and osmolality are critical in determining the central, rather than renal, nature of the defect in water homeostasis.

    • In adipsia, the fractional excretion of sodium is less than 1%, unless a coexisting defect in aqueous vasopressin (AVP) secretion is present.

    • Urine osmolality is very high, unless a coexisting defect in AVP secretion is present.

    • In diabetes insipidus, the concentration of urine is submaximal, even in the face of high serum osmolality. In salt intoxication, the urine sodium concentrations are very high and fractional excretion of sodium is greater than 1%.

    • Difficulties in diagnosis may arise when adipsia and diabetes insipidus coexist. In these patients, initial test results may be suggestive of diabetes insipidus; however, administration of AVP increases urine osmolality and diminishes the tendency for hypernatremia. The patient's history of absence of thirst points toward the coexistence of adipsia.

  • Blood hormone levels

  • AVP levels: In isolated adipsia, circulating AVP levels must be high, reflecting an appropriate response of the pituitary to hyperosmolality. In patients who have defects in thirst regulation and AVP secretion, serum AVP levels are low or absent.

  • Plasma renin and aldosterone levels: These are elevated secondary to hypovolemia.

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Imaging Studies

See the list below:

  • Brain imaging studies, such as CT scans and MRI studies, are indicated if the underlying cause for adipsia needs to be determined (eg, empty sella syndrome, tumor). They may also help to rule out complications of hypernatremia, such as intracranial hemorrhage.

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Other Tests

See the list below:

  • Therapeutic challenge with intravenous AVP or nasal desmopressin acetate (DDAVP) is often required to confirm or rule out the diagnosis of diabetes insipidus. Perform these tests in consultation with experts in water metabolism.

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