How does syndrome of inappropriate antidiuretic hormone secretion (SIADH) affect the anion gap?

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

The anion gap is reduced in SIADH secondary to equal dilution of serum Na+ and chloride, with unaffected bicarbonate (HCO3-). The anion gap is further decreased because the volume expansion probably reduces the tubular reabsorption of unmeasured anions, such as sulfate, phosphate, and urate.


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