Serum Osmolality

Plasma Osmolality Osmolarity
Serum (SST) mOsm/kg

About this test

Total solute concentration of serum. Calculated osmolality = 2×Na + Glucose + Urea (mmol/L). An osmolal gap >10 suggests unmeasured osmoles (alcohol, methanol, ethylene glycol).

Reference Ranges

Sex Age Range Notes
All ≥ 18 yrs 275 – 295 Adult; calculated vs measured used for osmolal gap

Clinical Interpretation

Low / Decreased
Low — hyponatraemia, overhydration.
High / Increased
High — dehydration, hypernatraemia, hyperglycaemia, uraemia, alcohol or toxic ingestion.

Related Tests

Specimen
Serum (SST)
Reporting Unit
mOsm/kg

⚠ Clinical Note
Reference ranges are indicative. Always interpret results in the context of the individual patient and local laboratory reference intervals, which may vary.