Excretion of electrolytes in the urine shows balance between anions (negatively charged) and cations (positively charged). Commonly measured electrolytes are sodium, potassium and chloride. The difference between measured cations (potassium and sodium) and anions (chloride) is termed the anion gap which is usually explained by ammonium (cation). In patients with acidosis the urine anion gap can indicate whether the acidosis is due to renal or nonrenal causes by reflecting ammonium excretion.
