II. Calculation
- Osmolar Gap = Serum Osms - Calculated Osmolality
- Normal Gap <10 to 15 mOsm/kg water
III. Causes: Elevated Osmolal Gap
-
Calculated Serum Osmolality > Measured Serum Osms
- Lab Error
- Mathematical error
- Measured Serum Osms > Calculated Serum Osmolality
- Decreased serum water (Calculated osmolality low)
- Hyperproteinemia
- Hypertriglyceridemia
- Presence of unmeasured Osms (Mnemonic: ME DIE)
- General
- Unmeasured osmoles are membrane permeant solutes
- Known as ineffective osmoles
- Do not affect water balance between ICF and ECF
- Methanol (decreased Blood pH)
- Ethylene Glycol (decreased Blood pH)
- Diuretics (Mannitol)
- Isopropanol or Isopropyl Alcohol (acetone detected)
- Ethanol
- Sorbitol
- Glycerol
- Acetone
- Ether trichloroethane
- Paraldehyde
- General
- Decreased serum water (Calculated osmolality low)
IV. Causes: Elevated Osmolal Gap with Metabolic Acidosis
- Precautions
- Note that Isopropanol (Isopropyl Alcohol) does not increase Anion Gap, but does increase Osmolal Gap
- Eythylene glycol
- Methanol
- Alcoholic Ketoacidosis
- Diabetic Ketoacidosis