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Osmolar GapAka: Osmolal Gap

See also
1. Serum Osmolality
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 (Mnemonic: 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. Glycerol
    9. Acetone
    10. Ether trichloroethane
    11. Paraldehyde

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This page was written by Scott Moses, MD. This page was last revised before 5/10/08, prior to consistent tracking of revision date. This page was last published on 6/1/2008. Please send comments and questions to the editor. Contact information may be found on the page About the Family Practice Notebook. These pages are best viewed with Microsoft Internet Explorer 6.0.