The myth of the low anion gap
R. J. Goldstein, N. S. Lichtenstein and D. Souder
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.
