Urine osmolality

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Urine osmolality
Medical diagnostics

Urine osmolality is a measure of urine concentration,[1] in which large values indicate concentrated urine and small values indicate diluted urine. Consumption of water (including water contained in food) affects the osmolality of urine.[2]

In healthy humans with restricted fluid intake, urine osmolality should be greater than 800 mOsm/kg, while a 24-hour urine osmolality should average between 500 and 800 mOsm/kg.

Urine osmolality in humans can range from approximately 50 to 1200 mOsm/kg, depending on whether the person has recently drank a large quantity of water (the lower number) or has gone without water for a long time (the higher number).[2] Plasma osmolality with typical fluid intake often averages approximately 290 mOsm/kg H2O in humans.[2]

In other animals[edit]

Some mammals are capable of higher osmolality than humans. This includes rats (approximately 3,000 mOsm/kg H2O), hamsters and mice (approximately 4,000 mOsm/kg H2O), and chinchillas (approximately 7,600 mOsm/kg H2O)

See also[edit]


  1. ^ "MedlinePlus Medical Encyclopedia: Osmolality - urine". Retrieved 2009-03-29. 
  2. ^ a b c Sands, Jeff M.; Layton, Harold E. (2014-01-01). "Advances in Understanding the Urine-Concentrating Mechanism". Annual Review of Physiology. 76 (1): 387–409. doi:10.1146/annurev-physiol-021113-170350. PMID 24245944.   – via Annual Reviews (subscription required)