mOsmol

mOsmol, short for milliosmole, is a unit used to express osmotic concentration. An osmole represents the amount of a solute that contributes to the osmotic pressure of a solution, and the number of osmoles depends on the degree of particle dissociation in solution. In practice, osmolality is commonly expressed as milliosmoles per kilogram of solvent (mOsm/kg), while osmolarity is expressed as milliosmoles per liter of solution (mOsm/L). Because many physiologically important solutes dissociate, osmoles, not moles, are the relevant measure of osmotic effect.

Measurement and calculation: Osmolality can be measured directly with an osmometer or estimated from the concentrations of major solutes in body fluids. A widely used approximate formula for plasma osmolality is Osm ≈ 2[Na+] + [glucose]/18 + [BUN]/2.8, with units in mOsm/kg. If ethanol or other unmeasured solutes are present, corrections may be added (for example, including ethanol/3.7). The difference between measured osmolality and calculated osmolality is called the osmolar or osmol gap, which can indicate additional solutes.

Physiological context and interpretation: Normal plasma osmolality is about 275–295 mOsm/kg. Deviations reflect hydration status and solute balance: hyperosmolality can occur with dehydration or hyperglycemia, while hypoosmolality may accompany hyponatremia or excessive water intake. Osmolality measurements are used in clinical.settings to assess volume status, electrolyte disorders, and certain poisonings.

History and terminology: The term mOsmol denotes milliosmoles, a non-SI unit commonly used in medicine to describe osmotic concentration. Although often reported as mOsm/kg for osmolality, the exact value depends on the solutes present and the measurement method.