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The anion gap is a method of assessing the contribution of unmeasured anions
to acidosis. It is calculated as a difference between the total of sodium and
potassium ion concentration, minus the total of chloride and bicarbonate concentration.
Some people omit the potassium. Thus: - Anion Gap = [K+] + [Na+]
- [Cl-] - [HCO3-] (plasma concentrations)
The normal range for the
anion gap is 6 - 16 mmol/l (1). The anion gap provides a measure of the difference
between unestimated anions - phosphate, acetate and ketones - and cations.
The anion gap is likely to abnormally high in most conditions of acidosis except: -
renal tubular acidosis
- treatment with acetazolamide
- ureteric
implantation into colon
Note that reference ranges may vary between
laboratories. Reference: - Joint
Pathology Services Royal Liverpool & Broadgreen University Hospitals (September
2006)
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