Send to

Choose Destination
Clin J Am Soc Nephrol. 2013 Nov;8(11):2018-24. doi: 10.2215/CJN.04040413. Epub 2013 Jul 5.

The serum anion gap in the evaluation of acid-base disorders: what are its limitations and can its effectiveness be improved?

Author information

Medical and Research Services, Veterans Affairs Greater Los Angeles Healthcare System, Los Angeles, California; , †Membrane Biology Laboratory, University of California, Los Angeles, California, ‡Division of Nephrology, Veterans Affairs Greater Los Angeles Healthcare System, David Geffen School of Medicine, Los Angeles, California.


The serum anion gap has been utilized to identify errors in the measurement of electrolytes, to detect paraproteins, and, most relevant to the nephrologist, to evaluate patients with suspected acid-base disorders. In regard to the latter purpose, traditionally an increased anion gap is identified when it exceeds the upper limit of normal for a particular clinical laboratory measurement. However, because there is a wide range of normal values (often 8-10 mEq/L), an increase in anion concentration can be present in the absence of an increased anion gap. In addition, the type of retained anion can affect the magnitude of the increase in anion gap relative to change in serum [HCO3(-)] being greater with lactic acidosis compared with ketoacidosis. This review examines the methods of calculation of the serum anion gap in textbooks and published literature, the effect of perturbations other than changes in acid-base balance, and its effectiveness in identifying mild and more severe disturbances in acid-base balance. Limitations of the present methods of determining the normal anion gap and change in the anion gap are highlighted. The possibility of identifying the baseline value for individuals to optimize the use of the calculation in the detection of metabolic acidosis is suggested.

[Indexed for MEDLINE]
Free PMC Article

Supplemental Content

Full text links

Icon for HighWire Icon for PubMed Central
Loading ...
Support Center