Syndrome of inappropriate antidiuretic hormone secretion

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

Clinical Features

Differential Diagnosis (Causes)


Essential Criteria[1]

  • Effective serum osmolality <275 mOsm/kg
  • Urine osmolality >100 mOsm/kg at some level of decreased effective osmolality
  • Clinical euvolaemia
  • 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 hyponatraemia after 0.9% saline infusion
  • Fractional sodium excretion >0.5%
  • Fractional urea excretion >55%
  • Fractional uric acid excretion >12%
  • Correction of hyponatraemia through fluid restriction




  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