The myth of the low anion gap.
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.
D000838:Anions; D001774:Blood Chemical Analysis; D002412:Cations; D003937:Diagnosis, Differential; D004573:Electrolytes / Q000097:blood*; D006801:Humans; D007010:Hyponatremia / Q000175:diagnosis*; D009101:Multiple Myeloma / Q000175:diagnosis; D011188:Potassium / Q000097:blood; D012709:Serum Albumin / Q000032:analysis; D012964:Sodium / Q000097:blood
D000838:Anions; D002412:Cations; D004573:Electrolytes; D012709:Serum Albumin; D012964:Sodium; D011188:Potassium