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Definition of Plasma osmolarity
Medically reviewed by Min Clinic Staff | Updated: January 2026
Plasma osmolarity: The osmolarity of blood plasma, which is a measure of the hydration status. The plasma osmolarity is sensitive to changes in hydration status during dehydration and rehydration. The normal plasma osmolarity is in the range of 280-300 mOs/kg. This may vary somewhat from laboratory to laboratory.