Osmolar Gap

• Calculation
  1. Osmolar Gap = Serum Osms - Calculated Osmolality
  2. Normal Gap <10 to 15 mOsm/kg water

   

   

• Causes Elevated Osmolal Gap
  1. Calculated Serum Osmolality > Measured Serum Osms
     1. Lab Error
     2. Mathematical error
  2. Measured Serum Osms > Calculated Serum Osmolality
     1. Decreased serum water (Calculated osmolality low)
        1. Hyperproteinemia
        2. Hypertriglyceridemia
     2. Presence of unmeasured Osms (Mneumonic: ME DIE)
        1. General
           1. Unmeasured osmoles are membrane permeant solutes
           2. Known as ineffective osmoles
           3. Do not affect water balance between ICF and ECF
        2. Methanol (decreased blood pH)
        3. Ethylene Glycol (decreased blood pH)
        4. Diuretics (Mannitol)
        5. Isopropyl alcohol (acetone detected)
        6. Ethanol
        7. Sorbitol
        8. Gylcerol
        9. Acetone
        10. Ether trichloroethane
        11. Paraldehyde