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Test ID UOSMU Osmolality, Urine

Reporting Name

Osmolality, U

Useful For

Assessing the concentrating and diluting ability of the kidney


Specimen Required


Supplies: Urine tubes, 10 mL (T068)

Container/Tube: Plastic, 10-mL urine tube

Specimen Volume: 5 mL

Collection Instructions: Collect a random urine specimen.


Specimen Minimum Volume

1 mL

Reference Values

0-11 months: 50-750 mOsm/kg

≥12 months: 150-1,150 mOsm/kg

Day(s) and Time(s) Performed

Monday through Sunday; Continuously

Test Classification

This test has been cleared or approved by the U.S. 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

83935

LOINC Code Information

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

 

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

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 if 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.

Interpretation

With normal fluid intake and normal diet, a patient will produce a 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 mOsm/kg/year.

 

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

 

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

Clinical Reference

Newman D, Price C: Renal function and nitrogen metabolites. In Tietz Textbook of Clinical Chemistry. Fourth edition. Edited by CA Burtis, ER Ashwood. Philadelphia, PA, WB Saunders Company, 2006

Analytic Time

Same day/1 day

Method Name

Freezing Point Depression

Specimen Type

Urine

Specimen Stability Information

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