Osmolality urine

Keywords: Urine Osmolality


Random urine specimen, without preservative.


Freezing point depression or vapour pressure depression.

Reference Interval:

Physiological range: 50-1,200 mmol/kg.


Renal disease, SIADH, and polyuric syndromes.


The kidneys can normally concentrate urine to an Osmolality of > 800 mmol/kg within 12 h of fluid restriction (Water deprivation test).

Comparison of serum and urine osmolalities may help to determine the cause of polyuria, to diagnose SIADH and to distinguish 'pre-renal' from 'renal' causes of impaired renal function.

See Osmolality.


Wong LL and Verbalis JG. Endocrinol Metab Clin North Am 2002; 31(1): 121-140.

Rose BD and Post TW. Clinical physiology of acid base and electrolyte disorders. 2001