Nephrology Book


Osmolar Gap

Aka: Osmolar Gap, Osmolal Gap
  1. See Also
    1. Sodium and Water Homeostasis
    2. Hyponatremia
    3. Hypernatremia
    4. Serum Sodium
    5. Total Body Sodium Deficit
      1. Includes Total Body Water and Free Water Deficit Calculations
    6. Serum Osmolality
    7. Urine Sodium
    8. Fractional Excretion of Sodium (FENa)
  2. Calculation
    1. Osmolar Gap = Serum Osms - Calculated Osmolality
    2. Normal Gap <10 to 15 mOsm/kg water
  3. 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
  4. 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
  5. References
    1. Braun (2015) Am Fam Physician 91(5): 299-307 [PubMed]

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
Derived from the NIH UMLS (Unified Medical Language System)

Osmolal gap result (C1318196)

Concepts Laboratory or Test Result (T034)
English Osmolal gap, osmolal gap, Osmolal gap result
Derived from the NIH UMLS (Unified Medical Language System)

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