The myth of the low anion gap

JAMA. 1980 May 2;243(17):1737-8.


Sixty-seven thousand seven hundred forty consecutive sets of electrolyte levels measured at the Massachusetts General Hospital were reviewed, and their anion gaps were calculated. A low anion gap (less than 8 mEq/L) was found in 304 patients (0.8%). Repeatedly low anion gaps were found in only 19 patients. Eight patients were hypoalbuminemic, and eight were hyponatremic. For the entire population, there was a positive correlation between sodium concentration and anion gap. The average anion gap was 16.25 mEq/L. The most common cause of a low anion gap was presumptive laboratory error.

MeSH terms

  • Anions*
  • Blood Chemical Analysis
  • Cations
  • Diagnosis, Differential
  • Electrolytes / blood*
  • Humans
  • Hyponatremia / diagnosis*
  • Multiple Myeloma / diagnosis
  • Potassium / blood
  • Serum Albumin / analysis
  • Sodium / blood


  • Anions
  • Cations
  • Electrolytes
  • Serum Albumin
  • Sodium
  • Potassium