LOW ANION GAP

Background. The purpose of this review is to provide a differential di agnosis for a low anion gap. Methods. We describe the anatomy of the a nion gap, Also, we follow-up with a review of the English-language lit erature describing the causes of a low anion gap. During the past 15 y ears, the introduction and widespread clinical use of ion-selective el ectrode 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 an ion 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 unrecog nized. Also, it may be a handy clinical clue for the diagnosis of life -threatening intoxications or occult neoplasms, such as multiple myelo ma. The baseline low anion gap may mask the identification of a high g ap metabolic acidosis in certain patients. Conclusions. Interpretation of a low anion gap can provide valuable clinical information.