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Serum anion gap in conditions other than 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 primarily used in the differential diagnosis of metabolic acidosis [1-4]. (See "Approach to the adult with metabolic acidosis", section on 'Physiologic interpretation of the serum anion gap'.)

However, the serum AG can also become abnormal in other conditions, a finding that may be of diagnostic importance [1-5].


The serum anion gap (AG) is calculated from the following formula:

 Serum AG  =  Measured cations - measured anions

Since Na is the primary measured cation and Cl and HCO3 are the primary measured anions (calculator 1):

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Literature review current through: Nov 2017. | This topic last updated: Jun 03, 2016.
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