II. Calculation

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

III. 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. Isopropanol or Isopropyl Alcohol (acetone detected)
      6. Ethanol
      7. Sorbitol
      8. Glycerol
      9. Acetone
      10. Ether trichloroethane
      11. Paraldehyde

IV. Causes: Elevated Osmolal Gap with Metabolic Acidosis

  1. Precautions
    1. Note that Isopropanol (Isopropyl Alcohol) does not increase Anion Gap, but does increase Osmolal Gap
  2. Eythylene glycol
  3. Methanol
  4. Alcoholic Ketoacidosis
  5. Diabetic Ketoacidosis

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Related Studies

Ontology: Osmolar gap (C0740329)

Concepts Laboratory Procedure (T059)
Italian Gap osmotico
Japanese 浸透圧ギャップ, シントウアツギャップ
Czech Osmolární gap
English Osmolar gap
Hungarian Ozmoláris rés
Portuguese Hiato osmolar
Spanish Desequilibro osmolar
Dutch osmolal gap
French Trou osmolaire
German Osmolaritaetsluecke

Ontology: Osmolal gap result (C1318196)

Concepts Laboratory or Test Result (T034)
English Osmolal gap, osmolal gap, Osmolal gap result