Serum Osmolality
Info
Na
unit mg/dL mmol/L
BUN
unit mg/dL mmol/L
Glucose
unit mg/dL mmol/L
R e s u l t s
mOsm/kg serum H20
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Serum Osmolality

Serum osmolality is used to categorize hyponatremias and calculate osmolal gap.

Formula used:

  • Serum Osmolality (Calculated) in mOsm/kg serum H20 = (2 * Na) + (BUN/2.8) + (Glu/18)
  • Na in mEq/L; BUN &Glu in mg/dL.
  • Normal = 285-295 mOsm/kg H20

The formula accounts for the most prevalent normally present osmotically active solutes.

Reference:

Work-Up of the Patient with an Acid-Base Disorder. In: Bryson PD. Comprehensive Review in Toxicology for Emergency Clinicians. 3rd ed. Washington, DC: Taylor & Francis; 1996:409-414.