Criteria
Diagnosis of SIADH[4][5][7]
Essential features:
Decreased effective serum osmolality (<275 mOsm/kg of H₂O)
Urinary osmolality >100 mOsm/kg of H₂O during hypotonicity
Urinary sodium >30 mEq/L with normal dietary salt and water intake
Clinical euvolemia
No orthostasis, tachycardia, decreased skin turgor, dry mucous membranes
No clinical signs of excessive volume, edema, or ascites
Normal thyroid and adrenal function
No recent diuretic use.
Supplemental features:
Plasma uric acid <4 mg/dL
BUN <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 mOsm/kg H₂O)
Elevated plasma arginine vasopressin (AVP) levels, despite the presence of hypotonicity and clinical euvolemia.
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