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Test ID UOSMM Osmolality, Urine

Specimen Required

Only orderable as a reflex. For more information see UAR / Urinalysis with Microscopic.


Container/Tube: Plastic urine container

Specimen Volume: 20 mL

Collection Instructions:

1. Collect a random urine specimen.

2. No preservative.

Useful For

Assessing the concentrating and diluting ability of the kidney as part of the urinalysis panel

Method Name

Only orderable as a reflex. For more information see UAR / Urinalysis with Microscopic.


Freezing Point Depression

Reporting Name

Osmolality, U

Specimen Type


Specimen Minimum Volume

1 mL

Specimen Stability Information

Specimen Type Temperature Time Special Container
Urine Refrigerated (preferred) 7 days
  Frozen  7 days

Clinical Information

Osmolality is an index of the solute concentration. Urine osmolality is a measure of the concentration of osmotically active particles, principally sodium, chloride, potassium, and urea; glucose can contribute significantly to the osmolality when present in substantial amounts in urine. Urinary osmolality corresponds to urine specific gravity in nondisease states.


The ability of the kidney to maintain both tonicity and water balance of the extracellular fluid can be evaluated by measuring the osmolality of the urine either routinely or under artificial conditions. More information concerning the state of renal water handling, or abnormalities of urine dilution or concentration, can be obtained if urinary osmolality is compared to serum osmolality, and urine electrolyte studies are performed. Normally, the ratio of urine osmolality to serum osmolality is 1.0 to 3.0, reflecting a wide range of urine osmolality.

Reference Values

Only orderable as a reflex. For more information see: UAR/ Urinalysis with Microscopic.


0-11 months: 50-750 mOsm/kg

≥12 months: 150-1,150 mOsm/kg


With normal fluid intake and normal diet, a patient will produce urine of about 500 to 850 mOsmol/kg water. Above age of 20 years, there is an age dependent decline in the upper reference range of approximately 5 mOsmol/kg/year.


The normal kidney can concentrate urine to 800 to 1,400 mOsmol/kg and with excess fluid intake, a minimal osmolality of 40 to 80 mOsmol/kg can be reached.


With dehydration, the urine osmolality should be 3 to 4 times the plasma osmolality.

Clinical Reference

1. Newman D, Price C: Renal function and nitrogen metabolites. In: Burtis CA, Ashwood ER, eds. Tietz Textbook of Clinical Chemistry. 4th ed. WB Saunders Company; 2006

2. Delaney MP, Lamb EJ: Kidney disease. In: Rifai N, Horvath AR, Wittwer CT, eds. Tietz Textbook of Clinical Chemistry and Molecular Diagnostics. 6th ed. Elsevier 2018:1306

Test Classification

This test has been cleared, approved, or is exempt by the US Food and Drug Administration and is used per manufacturer's instructions. Performance characteristics were verified by Mayo Clinic in a manner consistent with CLIA requirements.

CPT Code Information


LOINC Code Information

Test ID Test Order Name Order LOINC Value
UOSMM Osmolality, U 2695-5


Result ID Test Result Name Result LOINC Value
UOSMM Osmolality, U 2695-5

Day(s) Performed

Monday through Sunday

Report Available

1 day/Same day