Urinary Anion Gap in Hyperchloremic Metabolic Acidosis

To the Editor: In their article on the use of the urinary anion gap in assessing hyperchloremic metabolic acidosis, Batlle et al. (March 10 issue)¹ invite criticism on several counts. They claim that the more positive urinary anion gap (sodium plus potassium minus chloride) in patients with distal renal tubular acidosis than in acidotic “normal” controls was due to a lower urinary ammonium level. However, their own Table 1 shows that this made a minor contribution to the difference. Patients with distal tubular acidosis had a mean anion gap that was 58 mmol per liter more positive than that of.