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Osmolality measures solute concentration in body fluids. It's critical for diagnosing hyponatremia, hypernatremia, and fluid disorders.
Formule
Calculate: Osm = 2[Na] + (Glu/18) + (BUN/2.8)
- Na
- Na value — Variable used in the calculation
- BUN
- BUN value — Variable used in the calculation
Guide étape par étape
- 1Calculate: Osm = 2[Na] + (Glu/18) + (BUN/2.8)
- 2Normal: 280-310 mOsm/kg
- 3Compare measured to calculated osmolality
Exemples résolus
Entrée
Na 128, glucose 200, BUN 28
Résultat
Osm ≈ 318 (high), measured lower suggests hyponatremia
Pseudohyponatremia likely
Erreurs courantes à éviter
- ✕Neglecting glucose and BUN contributions in hyperglycemia/uremia
- ✕Confusing osmolality with osmolarity (different in concentrated solutions)
Questions fréquentes
What's the osmolal gap?
Difference between measured and calculated osmolality. Large gap suggests unmeasured osmoles (ethanol, methanol, etc.).
How does osmolality relate to sodium?
Sodium is the main determinant of osmolality; hyponatremia usually means hypoosmolality and vice versa.
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