What urine osmolality measurement confirms arginine vasopressin (AVP) excess?

Updated: Aug 16, 2019
  • Author: Christie P Thomas, MBBS, FRCP, FASN, FAHA; Chief Editor: Vecihi Batuman, MD, FASN  more...
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Answer

In SIADH, serum osmolality is generally lower than urine osmolality. In the setting of serum hypo-osmolality, AVP secretion is usually suppressed to allow the excess water to be excreted, thus moving the plasma osmolality toward normal. If AVP secretion is shut down completely, urine should have an osmolality of less than 100 mOsm. Therefore, urine osmolality of more than 100 mOsm in the context of plasma hypo-osmolality is sufficient to confirm AVP excess. Inappropriate water retention causes the dilutional hyponatremia.


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