Urine sodium and osmolality levels in pediatric disorders associated with hyponatremia classified by total body water

Total body water	Effective circulating volume	Urinary sodium concentration		Urine osmolality
Total body water	Effective circulating volume	<25 mEq/L	>40 mEq/L	<100 mOsm/kg	>100 mOsm/kg
Decreased (hypovolemia)	Decreased	Gastroenteritis Cystic fibrosis Diuretics – Late effect Burns Bleeding	Adrenal insufficiency Diuretics – Early effect Salt wasting SIADH		Gastroenteritis Cystic fibrosis Diuretics (early and late) Burns Bleeding Adrenal insufficiency Salt wasting SIADH Kidney function impairment (low GFR)
Normal (euvolemia) or increased (hypervolemia)	Decreased	Cardiac failure Nephrotic syndrome Cirrhosis			Cardiac failure Nephrotic syndrome Cirrhosis
Normal (euvolemia) or increased (hypervolemia)	Normal or increased		SIADH	Reset osmostat^* Water intoxication (primary polydipsia)	SIADH Kidney failure

ADH: antidiuretic hormone; GFR: glomerular filtration rate; SIADH: syndrome of inappropriate antidiuretic hormone.

* Patients with reset osmostat have a lower-than-normal threshold for ADH release. As a result, they are able to generate a dilute urine (urine osmolality below 100 mosmol/kg) when serum osmolality is below their lower-than-normal reset threshold for ADH in response to a water load.

Adapted from: Ashoor IF, Somers MJG. Physiology of the Developing Kidney: Fluid and Electrolyte Homeostasis and Therapy of Basic Disorders (Na/H2O/K/Acid Base). In: Pediatric Nephrology, 7th ed, Avner ED, Harmon WH, Niaudet P, et al. (Eds), Springer-Verlag, Berlin 2016.

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Urine sodium and osmolality levels in pediatric disorders associated with hyponatremia classified by total body water