Abbrev Code:OSM   
Order Code:LAB107Order Name:Osmolality
Methodology:Micro-osmometry by freezing point depression
CPT Codes: 83930 x1
Turnaround Time:Performed and reported 24 hours/day.

Collection Instructions

Optimal Volume:1 mL
Minimum\Peds Volume:0.5 mL
Container:Green (lithium heparin, gel), St Joseph - Green (lithium heparin, no gel)
Alternate Containers: Green (lithium heparin) on ICE, Green (sodium heparin, no gel), Red (no gel), Red or gold (gel), St. Joseph - Red (no gel)
Causes for Rejection:Frozen samples, samples greater than 48 hours old (refrigerated or room temperature).

Processing and Shipping

Specimen Processing:Separate the serum/plasma from cells ASAP. Centrifuge and aliquot 0.5 mL, 0.2 mL minimum. Store in refrigerator.
Shipping Instructions:Ship at refrigerated temperature.
Stability:Stability: 48 hours at room temperature or refrigerated.
Test Performed at or Referral Lab Chemistry  (CSC Mpls, Range, Southdale, UMMC East Bank, UMMC/UMMCH-West Bank)


Critical Range:Less than 250 mmol/kg and greater than 340 mmol/kg; greater than 385 mmol/kg relates to stupor in hyperglycemia; greater than 400 mmol/kg can relate to seizures; greater than 420 mmol/kg can be lethal.
Reference Range:0 - 5 months: 266-295 mmol/kg; 6 months - 59 years: 275-295 mmol/kg; 60 years and older: 280-301 mmol/kg
Use:Used for the detection of unmeasured substances in plasma or as an assessment of the concentrating ability of the kidney. Serum is also often used to monitor hyperalimentation administration as well as mannitol therapy on neurology patients.

Approximate osmolality can be calculated as follows: 2 x (sodium, mmol/L) + (glucose, mg/dL) / 2.8 + 9.  Osmolar gap = (calculated osmolality) - (measured osmolality).  Normally, the osmolar gap is less than 10 mmol/L. Gaps larger than this suggest unmeasured substances are present in the serum, e.g., ethanol, methanol, isopropanol, mannitol, or ethylene glycol.

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