How is urinary sodium concentration used in the diagnosis of hyponatremia?

Updated: Jun 17, 2019
  • Author: Eric E Simon, MD; Chief Editor: Vecihi Batuman, MD, FASN  more...
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Answer

 

Urinary sodium concentration helps differentiate between hyponatremia secondary to hypovolemia and syndrome of inappropriate antidiuretic hormone secretion (SIADH). With SIADH (and salt-wasting syndrome), the urine sodium is greater than 20-40 mEq/L. With hypovolemia, the urine sodium typically measures less than 25 mEq/L. However, if sodium intake in a patient with SIADH (or salt-wasting) happens to be low, then urine sodium may fall below 25 mEq/L.

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