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Test Code OSMO U Urine Osmolality

Clinical System Name

Urine Osmolality



Osmolality Urine


Urine osmolality, a measure of urine concentration, is used to help evaluate the body’s water balance. It is typically monitored to evaluate renal function, sodium balance, polyuria and oliguria.

Sample Requirements

Specimen:  Random urine

Container(s):  Sterile Screw-Capped Container

Preferred Vol: 0.5 mL

Minimum Vol: 0.1 mL


Note:  Sample MUST be at room temperature before centrifuging. Centrifuge urine to remove particulate matter which could accelerate crystallization. Deliver sample to Core Chemistry.

Processing Instructions

Reject due to: Non-sterile container, insufficient  quantity, incorrect storage temperature, age of specimen

Spin: Y

Aliquot: Y

Temp:  2o-4oC

Storage location: Core Chemistry Refrigerator


Off-site collection: Refrigerate sample (2o-4oC); stable for 24 hours.


Specimen Type Temperature Time
Urine RT 4 H
Urine 2o-4oC 24 H
Urine -20o or - 70oC 30 days



STAT Performed TAT
Y 24/7 1 H


Performing Laboratory

Seattle Children's Laboratory    


Department:  Core Chemistry

Phone Number:  206-987-2617



Reference Range


Age mOsm/kg
< 1 year 50 - 600
1 year - Adult 50 - 1400


The urine osmolality output varies greatly with diet.  Normal urine osmolality can be as much as 1400mOsm with maximal ADH stimulation, and as little as 50 with maximal ADH suppression. Thus, urine osmolarity should be interpreted in light of what is known about the patient's hydration status and plasma osmolarity.



Method:  Freezing Point Depression by Fiske Micro-Osmometer Model 210

Analytical Volume:  0.06 mL

CPT Codes