The Urinary Anion Gap
The cations normally present in urine are Na+, K+, NH4+, Ca++ and Mg++.
The anions normally present are Cl-, HCO3-, sulphate, phosphate and some organic anions.
Only Na+, K+ and Cl- are commonly measured in urine so the other charged species are the unmeasured anions (UA) and cations (UC).
Because of the requirement for macroscopic electroneutrality, total anion charge always equals total cation charge, so:
The cations normally present in urine are Na+, K+, NH4+, Ca++ and Mg++.
The anions normally present are Cl-, HCO3-, sulphate, phosphate and some organic anions.
Only Na+, K+ and Cl- are commonly measured in urine so the other charged species are the unmeasured anions (UA) and cations (UC).
Because of the requirement for macroscopic electroneutrality, total anion charge always equals total cation charge, so:
Cl- + UA = Na+ + K+ + UC
Rearranging: