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Anion Gap

The serum anion gap is the difference between the concentrations of the major cation, sodium and the major anions(Cl + HCO3). An electrolyte abnormality is often the first laboratory sign of an acid-base disorder. The anion gap measurement is likely to be most useful in emergency department in cases with ketoacidosis, lactic acidosis or renal failure.

 Serum Sodium (mmol/l)
 Serum Potassium(mmol/l)
 Serum Bicarbonate (mmol/l)
 Serum Chloride (mmol/l)
Anion Gap (mmol/l)


  • Normal Values:
    5-14 mmol/L (Only values < 2 and > 17 mmol/L are likely to be clinically significant).

    Acidosis can occur even when the anion gap is normal, as in the following cases:
    • gastrointestinal HCO3 loss; diarrhoea, fistulas etc.
    • increased Chloride; uterosigmoidostomy etc.
    • renal tubular acidosis
    • drugs, eg acetozolamide
    • administration of ammonium chloride
  • Increased anion gap could indicate:
    • renal failure:
      • increase in phosphate, sulphate
      • diabetic ketoacidosis,starvation ketoacidosis
      • lactic acidosis
    • poisonings:
      • methanol - formic acid metabolite
      • ethylene glycol - oxalic/glycolic acids
      • aspirin - salicylic acid

    In practice, an increased anion gap is usually due to an accumulation of unmeasured anions.
  • Decreased anion gap could indicate:
    • hypoalbuminemia.
    • marked increase in the cations.


The calculators provided in this section are for information purposes only. They are not meant to be a substitute for professional advise and are not to be used for medical diagnosis. The calculators provide only approximate values of the indices indicated and therefore should not be used for clinical or diagnostic purposes. www.webhealthcentre.com makes no claims whatsoever, expressed or implied, about the authenticity, accuracy, reliability, completeness or timeliness of the material, software, text, graphics and links given in this section. In no event shall www.webhealthcentre.com, its suppliers, affiliates or any third parties be liable in any manner whatsoever for any damages arising upon use of any information given in this section in any manner whatsoever.

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