Astrup P et al. The Acid-Base Metabolism. A New Approach. Lancet 1960; 1:1035-1039

Anderson WG. Gaps in the Data - Anions and Osmoles. Intensive Care World. 1988; 5: 92-93.

Badrick T & Hickman PE. The Anion Gap: A Reappraisal. Am J Clin Path 1992; 98: 249-252.

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) & 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 & 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.

DiNubile MJ. The Increment in the Anion Gap: Overextension of a Concept. The Lancet. 1988; 2: 951-953.

Emmett M & Narins RG. Clinical Use of the Anion Gap. Medicine. 1977; 56: 38-54.

Oh MS & Carroll HJ. The Anion Gap. New Engl J Med 1977; 297: 814-817.

Salem MM & Mujais SK. Gaps in the Anion Gap. Arch Int Med. 1992; 152: 1625-1629.