Reduced or absent serum anion gap as a marker of severe lithium carbonate intoxication

Two patients with life-threatening lithium carbonate intoxication (serum levels, greater than 4 mEq/L [greater than 4 mmol/L]) presented with a reduced or absent serum anion gap. In both subjects, hemodialysis simultaneously removed the excess lithium ion and normalized the anion gap. Conversely, the anion gap was normal in subjects with therapeutic serum lithium ion levels. Severe lithium carbonate intoxication should be added to the category of illnesses (multiple myeloma, bromide intoxication) causing a marked reduction in the anion gap. In the comatose patient, a reduced anion gap may serve as an important clinical clue to the presence of this drug intoxication.