Low anion gap.
BACKGROUND
The purpose of this review is to provide a differential diagnosis for a low anion gap.


METHODS
We describe the anatomy of the anion gap. Also, we follow-up with a review of the English-language literature describing the causes of a low anion gap. During the past 15 years, the introduction and widespread clinical use of ion-selective electrode methodology for measuring serum electrolyte values has caused a major fall in the normal range of the anion gap from 12 mEq/L +/- 4 mEq/L to 6 mEq/L +/- 3 mEq/L; therefore, a new definition for a low anion gap is in order.


RESULTS
Based on current clinical data, an anion gap value of < 3 mEq/L should be considered low. A low anion gap is a useful diagnostic tool, but its clinical significance is often unrecognized. Also, it may be a handy clinical clue for the diagnosis of life-threatening intoxications or occult neoplasms, such as multiple myeloma. The baseline low anion gap may mask the identification of a high gap metabolic acidosis in certain patients.


CONCLUSIONS
Interpretation of a low anion gap can provide valuable clinical information.
Medical Service, Veterans Affairs Medical Center, Emory University School of Medicine, Atlanta, GA 30033, USA.
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RL
Jurado
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del Rio
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Nassar
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Navarette
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Pimentel
D000136:Acid-Base Equilibrium; D000137:Acid-Base Imbalance / Q000097:blood* / Q000175:diagnosis* / Q000209:etiology; D015982:Bias; D003937:Diagnosis, Differential; D004573:Electrolytes / Q000097:blood; D006801:Humans; D017736:Ion-Selective Electrodes; D012016:Reference Values; D015203:Reproducibility of Results
D004573:Electrolytes