Anion Gap

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Latest Edit: Iva Lloyd, ND 2021-08-24 (EDT)

See Also Lab Tests

This value is a measurement of the difference between the sum of the serum cations (sodium and potassium) and the sum of the serum anions (CO2/bicarbonate and chloride).[1],[2]


  • The concentrations of other extracellular anions such as phosphates, sulfates, ketones, proteins, and lactic acid are all reflected in the difference measured. Acidosis is associated with an increase in these unmeasured anions.

Patient Preparation

  • Foods or fluids are not restricted.
  • Factors which can cause increased levels
  • Hemolyzed blood (anything that falsely decreases chloride or CO2, or falsely increases sodium or potassium), excessive intake of licorice (herbal)
  • Drugs: carbonic anhydrase inhibitors (e.g., acetazolamide), salicylate, spironolactone, triamterene, and methanol
  • Factors which can cause decreased levels
  • Anything that falsely increases chloride or CO2 or falsely decreases sodium or potassium, readings in infants, high triglycerides or low protein levels
  • Drugs: carbenicillin, penicillin phosphate, diuretics, antacids, licorice, and carbenoxolone

Clinical Implications

Ranges: The following are the reference ranges for this lab. However, lab ranges can vary by laboratory and country. [2]

Standard U.S. Units Standard International Units
Conventional Laboratory Range 6-16 mEq/L 6-16 mmol/L
Optimal Range 7-12 mEq/L 7-12 mmol/L
Alarm Ranges < 4 or > 25 mEq/L < 4 or > 25 mmol/L

High levels indicate

Low levels indicate

Associated Tests


  1. Pagana Kathleen D, Pagana Timothy J, (1998) Mosby's Manual of Diagnostic and Laboratory Tests, Mosby, Inc
  2. 2.0 2.1 Weatherby Dicken, Ferguson Scott (2002) Blood Chemistry and CBC Analysis: Clinical Laboratory Testing from a Functional Perspective, Bear Mountain