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Osmolality, urine


Osmolality , urine (Urine Osm)

Random: 100–900 mosm/kg H2O [mmol/kg H2O]

Urine container


Physiologic Basis

Test measures renal tubular concentrating ability.

Urine osmolality and specific gravity usually change in parallel with each other. When large molecules such as glucose and protein are present, however, the results diverge. Specific gravity is increased more, due to the weight of the molecules, whereas urine osmolality is increased less, reflecting the number of molecules.


Increased in: Hypovolemia, syndrome of inappropriate ADH secretion (SIADH). Drugs: anesthetic agents (during surgery), carbamazepine, chlorpropamide, cyclophosphamide, metolazone, vincristine.

Decreased in: Diabetes insipidus, primary polydipsia, exercise, starvation. Drugs: acetohexamide, demeclocycline, glyburide, lithium, tolazamide.


In the hypoosmolar state (serum osmolality < 280 mosm/kg), urine osmolality is used to determine whether water excretion is normal or impaired. A urine osmolality value of < 100 mosm/kg indicates complete and appropriate suppression of antidiuretic hormone secretion.

With average fluid intake, normal random urine osmolality is 100–900 mosm/kg H2O.

After 12-hour fluid restriction, normal random urine osmolality is > 850 mosm/kg H2O.

Capatina C et al. Diabetes insipidus after traumatic brain injury. J Clin Med 2015;4:1448.  [PMID: 26239685]

Oh JY et al. Syndrome of inappropriate antidiuretic hormone secretion and cerebral/renal salt wasting syndrome: similarities and differences. Front Pediatr 2015;2:146.  [PMID: 25657991]

Pasquel FJ et al. Hyperosmolar hyperglycemic state: a historic review of the clinical presentation, diagnosis, and treatment. Diabetes Care 2014;37:3124.  [PMID: 25342831]

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McPhee, Stephen J., et al. "Osmolality, Urine." Guide to Diagnostic Tests, 7th ed., McGraw-Hill Education, 2017. Anesthesia Central, anesth.unboundmedicine.com/anesthesia/view/GDT/619241/all/Osmolality__urine.
McPhee SJ, Lu CM, Nicoll D. Osmolality, urine. Guide to Diagnostic Tests. 7th ed. McGraw-Hill Education; 2017. https://anesth.unboundmedicine.com/anesthesia/view/GDT/619241/all/Osmolality__urine. Accessed April 19, 2019.
McPhee, S. J., Lu, C. M., & Nicoll, D. (2017). Osmolality, urine. In Guide to Diagnostic Tests. Available from https://anesth.unboundmedicine.com/anesthesia/view/GDT/619241/all/Osmolality__urine
McPhee SJ, Lu CM, Nicoll D. Osmolality, Urine [Internet]. In: Guide to Diagnostic Tests. McGraw-Hill Education; 2017. [cited 2019 April 19]. Available from: https://anesth.unboundmedicine.com/anesthesia/view/GDT/619241/all/Osmolality__urine.
* Article titles in AMA citation format should be in sentence-case
TY - ELEC T1 - Osmolality, urine ID - 619241 A1 - McPhee,Stephen J, AU - Lu,Chuanyi Mark, AU - Nicoll,Diana, BT - Guide to Diagnostic Tests UR - https://anesth.unboundmedicine.com/anesthesia/view/GDT/619241/all/Osmolality__urine PB - McGraw-Hill Education ET - 7 DB - Anesthesia Central DP - Unbound Medicine ER -