Serum Osmolality

• Normal
  1. Serum Osmolality: 280-300 mOsm/(kg water)

   

   

• Calculated Serum Osmolality
  1. Serum Osms = 2*Na + Glu/18 + BUN/2.8 + Et/4.6 + Man/18
  2. Annotation
     1. Where Na is Serum Sodium
     2. Where Glu is Serum Glucose
     3. Where BUN is Blood Urea Nitrogen
     4. Where Et is blood alcohol level
     5. Where Man is Mannitol

   

   

• Increased
  1. Dehydration
  2. Hypernatremia
  3. Diabetes Insipidus
  4. Uremia
  5. Hyperglycemia
  6. Mannitol
  7. Toxins
     1. Ethylene Glycol
     2. Methanol
     3. Alcohol

   

   

• Decreased
  1. SIADH
  2. Hyponatremia
  3. Overhydration