Positively charged cations - negatively charged anions
Na + K - Cl + HCO3
Normal range = 3-11 (>14 typically indicates a rasied anion gap acidosis)
Cations and anions should = 0
It wont be 0 as Na and K account for most of the Cations but in this formula, a number of anions are ignored - sulphate, phosphate, organic acids, negatively charged proteins like albumin
Therefore if the anion gap is high it means these other anions account for a greater proportion of the serums negative charge then usual
Acidosis can be classified as
High anion gap:
Example - lactic acidosis
lactic acid production in solution gives a H+ and a negatively charged ion, the H+ is buffered with bicarb, lowering the amount of bicarb. So now theres more lactate and less bicarb accounting for it.
The anion gap will increase as an increased proportion of the negative charge is not accounted for in the anion gap calculation