Anion Gap (serum) is expressed in mEq/L (mmol/L) and is the indirect measurement of serum anions (proteins, phosphate, sulphate and organic anions) not measured by routine lab tests.
This formula includes only Na+, Cl- and HCO3, other formulas include the K+ as well, see
* Increased AG acidosis: Renal insufficiency, ketoacidosis (diabetic or ETOH), lactic acidosis and drug intoxications (methanol, ethylene glycol,salicylates, paraldehide, etc). Sometimes, the AG_S may decrease as a result of accumulation of cationic proteins (myeloma) then an increase in the AG equivalent to the decrease in HCO₃ strongly suggests the presence of a high AG metabolic acidosis.