OzEMedicine - Wiki for Australian Emergency Medicine Doctors

see also:

• arterial and venous blood gases (ABGs/VBGs)
• metabolic acidosis

• 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

• 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.

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

• 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