How does syndrome of inappropriate antidiuretic hormone secretion (SIADH) affect urine osmolality?

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

Patients with hyponatremia should turn off ADH and have a urine that is maximally dilute (ie, 50-100 mOsm/kg); however, in patients with SIADH, the urinary osmolality is usually submaximally dilute (ie, >100 mOsm/kg). One of the more common errors in recognizing SIADH is the failure to realize that the urine’s osmolality must be only inappropriately elevated and not necessarily greater than the corresponding serum osmolality.


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