What can affect the anion gap (AG) in the workup of metabolic acidosis?

Updated: Oct 05, 2018
  • Author: Antonia Quinn, DO; Chief Editor: Romesh Khardori, MD, PhD, FACP  more...
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Answer

The AG can rise because of increases in unmeasured anions or decreases in unmeasured cations (eg, hypokalemia, hypocalcemia, hypomagnesemia). AG can also increase, secondary to an increase in albumin or an increase in negative charges on albumin, which is caused by alkalosis.

AG can be decreased by an increase in unmeasured cations (eg, hyperkalemia, hypercalcemia, hypermagnesemia, lithium intoxication, high immunoglobulin G [IgG] levels), or by a decrease in unmeasured anions (eg, hypoalbuminemia).

Finally, laboratory errors can also affect the AG. Hyperproteinemia, hyperlipidemia, and hyperglycemia resulting in underestimation of serum sodium level can falsely depress AG. In addition, bromide intoxication can be mistaken for Cl-, which can result in an inappropriate depression of the AG.


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