Syndrome of inappropriate antidiuretic hormone secretion

(Redirected from SIADH)


  • Abbreviation: SIADH
  • Inappropriate or continued action of ADH despite normal/increased plasma volume→ impaired water excretion→ hyponatremia and hypo-osmolality

Clinical Features

  • See hyponatremia
  • Symptoms of neoplasm, particularly lung neoplasm

Differential Diagnosis (Causes)


Essential Criteria[1]

  • Effective serum osmolality <275 mOsm/kg
  • Urine specific gravity > 1.015
  • Urine osmolality >100 mOsm/kg at some level of decreased effective osmolality
  • Clinical euvolemia
  • Urine sodium concentration >30 mmol/l with normal dietary salt and water intake
  • Absence of adrenal, thyroid, pituitary or renal insufficiency
  • No recent use of diuretic agents

Supplemental criteria

  • Serum uric acid <0.24 mmol/l (<4mg/dl)
  • Serum urea <3.6 mmol/l (<21.6mg/dl)
  • Failure to correct hyponatremia after 0.9% saline infusion
  • Fractional sodium excretion >0.5%
  • Fractional urea excretion >55%
  • Fractional uric acid excretion >12%
  • Correction of hyponatremia through fluid restriction


  • See hyponatremia
  • Fluid restriction
  • Oral salt tablets (NaCl) for mild-moderate hyponatremia
  • 100 cc bolus of 3% NaCl for severe symptoms, repeat if neurologic symptoms persist or worsen
    • Ideally given through central line
  • DO NOT give normal saline 0.9%
    • In SIADH, sodium handling is intact and renal system will excrete Na
    • Water handling out of balance from excessive ADH
    • All sodium will be excreted, urine osmolality will remain high
    • Half of the bolus of normal saline will be retained, worsening hyponatremia
  • See osmotic demyelination syndrome for excessively rapid overcorrection



  1. Schwartz WB, Bennett W, Curelop S, Bartter FC. A syndrome of renal sodium loss and hyponatremia probably resulting from inappropriate secretion of antidiuretic hormone. American Journal of Medicine 1957 23 529–542
  2. Verbalis JG et al. Diagnosis, evaluation, and treatment of hyponatremia: expert panel recommendations. Am J Med. 2013 Oct;126(10 Suppl 1):S1-42.