Hyponatremia: Evolving diagnostics and emerging therapeutics in clinical practice

Table 2 Comparison of syndrome of inappropriate antidiuretic hormone, cerebral salt wasting, and reset osmostat

Feature	SIADH	Cerebral salt wasting	Reset osmostat
Volume status	Euvolemic	Hypovolemic (true salt loss)	Euvolemic
Plasma sodium	Low	Low	Mildly low but stable
Urine sodium	> 30 mmol/L	> 30 mmol/L	Variable
Urine osmolality	> 100 mOsm/kg	> 100 mOsm/kg	Normal dilution capacity maintained
Serum uric acid	Low	Low	Normal or low-normal
Fractional excretion of uric acid	Elevated during hyponatremia (> 12%), normalizes after correction	Remains elevated after correction	Normal (< 11%)
Fractional excretion of sodium	> 0.5%-1% (inappropriately high for euvolemia)	> 1%-2% (due to true renal salt loss)	Normal or slightly increased
Fractional excretion of urea	> 55%-60%	> 60%-70%	Normal (< 35%)
Response to isotonic saline	No improvement or worsens hyponatremia	Improves serum sodium and volume	No major change
ADH secretion pattern	Inappropriate, independent of osmolality	Appropriate (secondary to hypovolemia)	Reset to a lower threshold
Volume markers (BUN, hematocrit)	Normal	Elevated (due to hypovolemia)	Normal
Treatment approach	Fluid restriction, salt tablets, urea, vaptans	Volume and salt repletion ± fludrocortisone	Usually none; avoid overcorrection
Typical setting	Pulmonary disorders, malignancy, CNS disease, drugs	CNS injury, subarachnoid hemorrhage, neurosurgery	Chronic illness, elderly, pregnancy, tuberculosis, carcinoma

ADH: Antidiuretic hormone; BUN: Blood urea nitrogen; CNS: Central nervous system.