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The Δanion gap/ΔHCO3 ratio in patients with a high anion gap metabolic acidosis

Michael Emmett, MD
Section Editor
Richard H Sterns, MD
Deputy Editor
John P Forman, MD, MSc


Determination of the serum anion gap (AG) is an important step in approaching the differential diagnosis of metabolic acidosis [1-5]. (See "Approach to the adult with metabolic acidosis", section on 'Physiologic interpretation of the serum anion gap'.)

The serum AG is calculated from the following formula, which represents the difference between the primary measured cation (Na) and the primary measured anions (Cl and HCO3):

   Serum AG  =  Na  -  (Cl  +  HCO3)

Some clinicians also include the serum potassium in the formula; when this is done, the normal range increases by about 4 meq/L:

   Serum AG  =  (Na  +  K)  -  (Cl  +  HCO3)


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Literature review current through: Sep 2016. | This topic last updated: Jun 17, 2014.
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