Calculators for the evaluation of the anion gap, delta gap, and delta ratio in patients with metabolic acidosis.
Anion Gap Formula / Calculator
[Na] – ([Cl] + [HCO3])
Interpretation of the results of anion gap (albumin or non-albumin corrected)
Anion Gap | Causes |
High Anion Gap due to excess acid (AG >16) | Lactic acidosis |
Ketoacidosis - starvation ketosis, alcohol or diabetic ketoacidosis | |
Uremia | |
Methanol or Ethanol | |
Rhabdomyolysis | |
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 | |
Cholestyramine/Acetazolamide | |
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 ratio | Interpretation |
0 to 0.4 | Hyperchloremic normal/non-anion gap acidosis |
0.4 to 1.0 | High anion gap acidosis and normal anion gap acidosis |
1 to 2 | High anion gap acidosis |
>2 | High 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 Gap | Interpretation |
<18 | Concomitant non-anion gap metabolic acidosis |
18-30 | No additional metabolic perturbations |
>30 | Concomitant metabolic alkalosis |
References
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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