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Osmolality, Urine

Urine Osmolality

Test Codes

24-Hour Urine: EPIC: LAB56772, Beaker: OSM24, Random Urine: EPIC: LAB5098, Beaker: OSMOU, Antrim: 15835

Department

Chemistry

Instructions

Note: 24-hour and random urine specimens MUST be collected separately. See below for collection criteria.

• Please refer to the Specimen Collection Manual for instructions on 24-Hour or Random Urine Collection: 
  • Urine 24-Hour Collection - Inpatient  
  • Urine 24-Hour Collection - Outpatient  
  • Urine 24-Hour Collection - Outreach
  • Random Urine Collection 

Specimen Collection Criteria

Collect: 24-hour urine or timed urine specimen with a 24-hour urine container with no preservatives.

Also acceptable: Random urine specimen in a screw-capped container (preferred) or another sterile collection cup. Preservatives are not acceptable for random urine specimens. (Minimum: 20 mL)

• Refer to the table of Urine Preservative Options when multiple tests are requested. 
• Keep 24-hour urine specimen iced or refrigerated during collection. 
• Include start and end dates and times for the collection period on the specimen container.  

Urine Preservative Options
No Preservative	6N Hydrochloric Acid	Boric Acid (10g)	Sodium Carbonate	50% Acetic Acid
Required	Unacceptable	Unacceptable	Unacceptable	Unacceptable

Physician Office/Draw Specimen Preparation

Maintain specimens capped and refrigerated (2-8°C or 36-46°F) prior to transport.

Preparation for Courier Transport

Transport: Random urine, or entire 24-hour urine collection, refrigerated (2-8°C or 36-46°F).

Rejection Criteria

Specimens not collected and processed as indicated.  

In-Lab Processing

• Keep specimen capped to prevent evaporation or loss of volatile substances. 
• Centrifuge random urine specimens. 
• Measure total volume of 24-hour urine specimen. Record total volume and collection start and end dates and times in the LIS system. Aliquot a minimum of 10 mL from the well-mixed 24-hour urine collection. 

Storage

Specimen Stability for Testing:

Room temperature (20-26°C or 68-78.8°F): 4 hours
Refrigerated (2-8°C or 36-46°F): 7 days
Frozen (-20°C/-4°F or below): For longer storage.

Specimen Storage in Department Prior to Disposal:

Refrigerated (2-8°C or 36-46°F): 7 days (Royal Oak and Troy store an aliquot for 30 days.)

Laboratory

Dearborn Chemistry Laboratory
Farmington Hills Chemistry Laboratory
Grosse Pointe Chemistry Laboratory

Royal Oak STAT/Automated Chemistry Laboratory
Troy Chemistry Laboratory

Performed

Random Urine Specimens
Sunday – Saturday, 24 hours a day.
STAT results available within 1 hour of receipt in the Laboratory.
Routine results available within 24 hours.

24-Hour Urine Specimens
Sunday – Saturday.
Results available within 24 hours.

Reference Range

Random Urine: 50-1200 mOsmol/kg.

24-Hour Urine: 300-900 mOsmol/kg.

Test Methodology

Freezing Point Depression.

Clinical Utility

Urine osmolality is used to assess the concentrating ability of the kidney. The result of urine osmolality should be assessed in conjunction with serum/plasma osmolality and clinical information. For instance, if a patient is dehydrated with a high-normal serum osmolality then a urine osmolality of 200 mOsm/kg is inappropriate and abnormal.

CPT Codes

83935

Contacts

Last Updated

11/2/2023