Osmolality Calculation

Sunquest Code:N/A  
Test Includes:For information only; this value is not reported by laboratory.

Collection Instructions

Specimen:Calculated from determination of sodium, glucose, and urea nitrogen.
Container:Green (sodium heparin, no gel)

Processing and Shipping

Test Performed at or Referral Lab Chemistry  (UMMC-East Bank)


Reference Range:Approximate osmolality can be calculated as follows: 2 x (sodium, mmol/L) + (glucose, mg/dL)/18 + (urea nitrogen, 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.
Use:Compare calculated osmolality to measured osmolality

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