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anion_gap

anion gap

introduction

  • anion gap is a calculated quantity used to assist in the Dx of metabolic acidosis
  • anion gap = ( [Na+]+[K+] ) − ( [Cl−]+[HCO3−] )
  • the average anion gap for healthy adults is 8-12 mEq/L

high anion gap

  • a high anion gap indicates that there is loss of HCO3− without a concurrent increase in Cl−.
  • electroneutrality is maintained by the elevated levels of anions like lactate, beta-hydroxybutyrate and acetoacetate, PO4−, and SO4−. These anions are not part of the anion-gap calculation and therefore a high anion gap results.

normal anion gap with metabolic acidosis

  • the drop in HCO3− is compensated for almost completely by an increase in Cl− and hence is also known as hyperchloremic acidosis.

low anion gap

  • most commonly due to hypoalbuminaemia as reduction in the negatively charged albumin results in an increase in bicarbonate and chloride ions to retain electroneutrality.
    • in hypoalbuminaemia the anion gap is reduced from between 1.5 and 2.5 mmol/L per g/dL decrease in serum albumin
  • may occur in multiple myeloma due to raised plasma IgG
anion_gap.txt · Last modified: 2010/01/18 13:44 (external edit)