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March 21, 1977

Small Anion Gaps

JAMA. 1977;237(12):1200. doi:10.1001/jama.1977.03270390016007

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To the Editor.—  We certainly enjoyed being dealt a hand in the game of the gaps (236:1594, 1976) and will only comment on the paragraph discussing small anion gaps.In addition to multiple myeloma with paraproteinemia as a cause of a low gap, three other possibilities exist: (1) A small gap is most commonly a clue to the clinician that laboratory error exists and that a second blood electrolyte study is warranted. (2) In the situation where marked hypernatremia is present, the automated system of chemical analysis has accuracy difficulty and generally undervalues the serum sodium level, thereby artifactually subtracting cations from the gap equation. (3) Finally, a small anion gap may be the only tip towards making a diagnosis in the mentally deranged patient; bromide is measured as chloride by the automated system of chemical analysis and adds measured anions, thus decreasing the gap.