What is anion gap?

Anion gap represents apparent disparity between the total cation concentration and the total anion concentration in plasma.

·        The normal cations present in plasma are Na⁺, K⁺, Ca⁺⁺ Mg⁺⁺

·        The normal anions present in plasma are Cl^-, HCO₃, and negative charges present on albumin, phosphate, sulphate, lactate and other organic acids.

The sum of total cations and anions are equal.

[Na⁺ + K⁺] + Unmeasured cations = [HCO₃ + Cl] + Unmeasured anions

[Na⁺ + K⁺] -- [HCO₃ + Cl] = UA – UC = Anion Gap.

So anion gap = UA – UC = 24 – 9 = 15 mEq/L

The normal anion gap is 10 to 18 mEq/L.