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Test Code LAB420 Osmolality, Urine

Performing Laboratory

St. Louis Children's Hospital - Chemistry

Specimen Requirements

Patient Preparation: None

Container/Tube  
Preferred/Acceptable: A clean, plastic screw-cap urine collection container with no preservative

Collection Volume: 2.0 mL (minimum 0.3 mL)

Submission Container/Tube: If specimen is coming from outside facility aliquot sample into a plastic vial for transport (labeling with specimen type).
Special Instructions: Keep at ambient temperature and send to lab promptly. 

Sample Rejection

Mislabeled or unlabeled specimens

Logistics

Test Availability: Monday-Sunday
Cut-off time: None; performed as received
Turnaround Time: Same day; 2 hours from receipt in performing lab

Reference Values

Therapeutic Range: No reference values established

Critical Values: None established

Methodology

Freezing Point Depression

Limitations

  • Hemoglobin and other intracellular components will falsely elevate the osmolality.

 

Additional Information

FOR SLCH CORE LABORATORY USE ONLY

Lab Processing Instructions: Specimen does not need to be spun unless it appears bloody, in which case, centrifuge specimen to clear and aliquot supernatant into a plastic tube for testing.
Processed Volume: 2.0 mL (minimum 0.3 mL) urine
Analyte Stability:

Specimen Type Temperature Time  
Urine (no preservative)     Ambient 6 hours  
  Refrigerated     24 hours  
  Frozen  3 months       

 

NOTE: keep sample at ambient temperature prior to testing or if being added onto a refrigerated or frozen specimen make sure it is ambient temperature for testing.

Test Classification and CPT Coding

83935

LOINC

57372-5

Last Reviewed

06/2025