Criteria

Diagnosis of SIADH[4][5]​​[7]​​

Essential features:

  • Decreased effective serum osmolality (<275 mmol/kg [<275 mOsm/kg] of H₂O)

  • Urinary osmolality >100 mmol/kg H₂O (>100 mOsm/kg of H₂O) during hypotonicity

  • Urinary sodium >30 mmol/L (>30 mEq/L) with normal dietary salt and water intake

  • Clinical euvolaemia

  • No orthostasis, tachycardia, decreased skin turgor, dry mucous membranes

  • No clinical signs of excessive volume, oedema, or ascites

  • Normal thyroid and adrenal function

  • No recent diuretic use.

Supplemental features:

  • Plasma uric acid <0.24 mmol/L (<4 mg/dL)

  • Serum urea <3.6 mmol/L (<10 mg/dL)

  • Fractional sodium excretion >1%, fractional urea excretion >55%

  • Failure to correct serum sodium with normal saline infusion

  • Abnormal result on test of water load (<80% excretion of 20 mL of H₂O/kg body weight over 4 hours), or inadequate urinary dilution (<100 mmol/kg H₂O or <100 mOsm/kg H₂O)

  • Elevated plasma arginine vasopressin (AVP) levels, despite the presence of hypotonicity and clinical euvolaemia.

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