Osmolality - urine

Last updated: Monday, 22, March, 2004

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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 hours 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 - serum.


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