Fluid BalanceUpdated 2025-12-24Medically Reviewed
Serum Osmolality
Everything you need to know about Serum Osmolality levels, including what normal ranges look like and what abnormal results might indicate.
Standard Reference Range
Unit: mOsm/kgMale Reference Range
275–295 mOsm/kg
Female Reference Range
275–295 mOsm/kg
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Reference ranges may vary slightly between laboratories. Always consult your doctor for interpretation.
What is Serum Osmolality?
Serum osmolality measures the concentration of dissolved particles (electrolytes, glucose, urea) in blood and reflects hydration status.
Key Takeaway
The “osm gap” (measured minus calculated) helps detect toxic alcohols or unmeasured solutes.
Why is this test performed?
- Evaluate unexplained confusion, seizures, or coma
- Diagnose hyponatremia causes (SIADH, dehydration)
- Screen for toxic alcohol ingestion
Interpreting Your Results
- Low (＜275): Overhydration, SIADH
- High (＞295): Dehydration, high glucose, urea, or alcohol/ethylene glycol
Related Tests
- Sodium/Glucose/BUN: Inputs for calculated osmolality
- Bicarbonate: Assesses accompanying acid-base changes
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