Essential features |
Decreased effective osmolality (<275 mOsm/kg of water) |
Urinary osmolality > 100 mOsm/kg of water during hypotonicity |
Clinical euvolemia |
No clinical signs of volume depletion of extracellular fluid |
No orthostasis, tachycardia, decreased skin turgor, or dry mucous membranes |
No clinical signs of excessive volume of extracellular fluid |
No edema or ascites |
Urinary sodium > 40 mmol/liter with normal dietary salt intake |
Normal thyroid and adrenal function |
No recent use of diuretic agents |
Supplemental features |
Plasma uric acid < 4 mg/dl |
Blood urea nitrogen < 10 mg/dl |
Fractional sodium excretion > 1%; fractional urea excretion > 55% |
Failure to correct hyponatremia after 0.9% saline infusion |
Correction of hyponatremia through fluid restriction |
Abnormal result on test of water load (<80% excretion of 20 ml of water per kilogram of body weight over a period of 4 hours), or inadequate urinary dilution (<100 mOsm/kg of water) |
Elevated plasma AVP levels, despite the presence of hypotonicity and clinical euvolemia |