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Osmolality measures solute concentration in body fluids. It's critical for diagnosing hyponatremia, hypernatremia, and fluid disorders.
Formel
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
Trinn-for-trinn guide
- 1Calculate: Osm = 2[Na] + (Glu/18) + (BUN/2.8)
- 2Normal: 280-310 mOsm/kg
- 3Compare measured to calculated osmolality
Løste eksempler
Inndata
Na 128, glucose 200, BUN 28
Resultat
Osm ≈ 318 (high), measured lower suggests hyponatremia
Pseudohyponatremia likely
Vanlige feil å unngå
- ✕Neglecting glucose and BUN contributions in hyperglycemia/uremia
- ✕Confusing osmolality with osmolarity (different in concentrated solutions)
Ofte stilte spørsmål
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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