title: The use of the urinary anion gap in the diagnosis of hyperchloremic metabolic acidosis.
abstract: We evaluated the use of the urinary anion gap (sodium plus potassium minus chloride) in assessing hyperchloremic metabolic acidosis in 38 patients with altered distal urinary acidification and in 8 patients with diarrhea. In seven normal subjects given ammonium chloride for three days, the anion gap was negative (-27 +/- 9.8 mmol per liter) and the urinary pH under 5.3 (4.9 +/- 0.03). In the eight patients with diarrhea the anion gap was also negative (-20 +/- 5.7 mmol per liter), even though the urinary pH was above 5.3 (5.64 +/- 0.14). In contrast, the anion gap was positive in all patients with altered urinary acidification, who were classified as having classic renal tubular acidosis (23 +/- 4.1 mmol per liter, 11 patients), hyperkalemic distal renal tubular acidosis (30 +/- 4.2, 12 patients), or selective aldosterone deficiency (39 +/- 4.2, 15 patients). When the data on all subjects studied were pooled, a negative correlation was found between the urinary ammonium level and the urinary anion gap. We conclude that the use of the urinary anion gap, as a rough index of urinary ammonium, may be helpful in the initial evaluation of hyperchloremic metabolic acidosis. A negative anion gap suggests gastrointestinal loss of bicarbonate, whereas a positive anion gap suggests the presence of altered distal urinary acidification.
authors.affiliation: Department of Medicine (Nephrology Section), Northwestern University Medical School, Chicago, IL 60611.
authors.forename: D C
authors.initials: DC
authors.lastname: Batlle
authors.forename: M
authors.initials: M
authors.lastname: Hizon
authors.forename: E
authors.initials: E
authors.lastname: Cohen
authors.forename: C
authors.initials: C
authors.lastname: Gutterman
authors.forename: R
authors.initials: R
authors.lastname: Gupta
mesh_terms: D000136:Acid-Base Equilibrium; D000138:Acidosis / Q000175:diagnosis / Q000652:urine*; D000141:Acidosis, Renal Tubular / Q000652:urine; D000641:Ammonia / Q000652:urine; D000643:Ammonium Chloride / Q000378:metabolism; D002712:Chlorides / Q000097:blood*; D003967:Diarrhea / Q000652:urine; D006801:Humans; D006863:Hydrogen-Ion Concentration; D006994:Hypoaldosteronism / Q000652:urine; D011188:Potassium / Q000097:blood / Q000652:urine; D012964:Sodium / Q000652:urine
chemical_list: D002712:Chlorides; D000643:Ammonium Chloride; D000641:Ammonia; D012964:Sodium; D011188:Potassium