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Test Code Osmo Osmolality Serum

Clinical System Name

Osmolality Serum

Sample Requirements

Specimen:  Serum or Plasma

Container(s):  Gold SST, Red Tube, Dark Green/Sodium Heparin or Lt. Green/Lithium Heparin

Preferred Vol: 1 mL

Minimum Vol:  1 Lt. Green/Lithium Heparin Microtainer or 1 Gold Microtainer


Note:  Sample should be at room temperature before testing. If it is necessary to refreeze a specimen, allow it to return to room temperature before re-testing. The presence of cells accelerates crystallization and should be avoided.


Processing Instructions

Reject due to:  Age of specimen, incorrect collection container

Spin: Y

Aliquot:  Y

Temp: 2-8oC

Storage location:  Core Chemistry Refrigerator


Off-site collection:  Spin sample, remove serum or plasma from cells. Refrigerate sample; stable for approximately 3 days. Freeze for longer storage.



Specimen Type Temperature Time
Serum or Plasma RT

24 H

Serum or Plasma 2-8oC

24 H

Serum or Plasma -20o C or -70oC

30 D



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 Reference (mOsm/kg)
1 M 274 - 305
> 1 M 275 - 300



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

Minimum Volume:  0.5 mL serum or plasma 

CPT Codes


Critical Values

265 mOsm/kg 


≥ 320 mOsm/kg