Anion Gap Formula and Calculator

Calculators for the evaluation of the anion gap, delta gap, and delta ratio in patients with metabolic acidosis.

AGP formula

Required biochemical parameters

Enter serum sodium, chloride, bicarbonate and albumin

Generated Results

The results of Anion Gap, Albumin Corrected Anion Gap, Delta Gap and Delta Ratios will be generated below

Anion Gap Formula / Calculator

[Na] – ([Cl] + [HCO3])

Delta gap = Anion Gap – Baseline gap. Note that baseline gap = 12
Delta ratio = Delta gap / (24 – [HCO3])

Interpretation of the results of anion gap (albumin or non-albumin corrected)

Anion GapCauses
High Anion Gap due to excess acid (AG >16)Lactic acidosis
Ketoacidosis - starvation ketosis, alcohol or diabetic ketoacidosis
Methanol or Ethanol
Salicylate toxicity
Isoniazid/Paraldehyde/Iron toxicity
Normal Anion Gap due to renal or extra-renal (gastrointestinal) losses of bicarbonate (AG 8-16)GI losses (enterocutaneous fistula, diarrhea, colostomy, ileostomy)
Isotonic saline infusion
Renal tubular acidosis (type I or IV)
Uteropelvic shunt
Addison's disease
Low anion gap (<8)Albumin (decreased unmeasured anions)
Calcium, magnesium, lithium (increased unmeasured cations)
Laboratory error

Interpretation of the results of delta ratio 

Delta ratioInterpretation
0 to 0.4Hyperchloremic normal/non-anion gap acidosis
0.4 to 1.0High anion gap acidosis and normal anion gap acidosis
1 to 2High anion gap acidosis
>2High anion gap acidosis with co-existing metabolic alkalosis or fully compensated respiratory acidosis

Interpretation of the results of delta gap (albumin or non-albumin corrected)

Delta GapInterpretation
<18Concomitant non-anion gap metabolic acidosis
18-30No additional metabolic perturbations
>30Concomitant metabolic alkalosis


Oh MS, Carroll HJ. The anion gap. N Engl J Med. 1977 Oct 13;297(15):814-7. doi: 10.1056/NEJM197710132971507. PMID: 895822.

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The MyEndoconsult Team. A group of physicians dedicated to endocrinology and internal medicine education.

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