The anion gap helps classify the cause of a metabolic acidosis by checking whether unmeasured acids are present — an essential companion to interpreting an ABG alongside CO₂ and pH.
Normal anion gap.
Mildly elevated.
High anion gap — added acids likely.
Markedly elevated.
A metabolic acidosis triggers respiratory compensation (faster, deeper breathing), so understanding the metabolic side helps explain what's driving a patient's respiratory pattern.
Roughly 8–12 mEq/L, though the reference range varies slightly by lab and by whether potassium is included.
Added unmeasured acids — lactic acidosis, ketoacidosis, kidney failure (uremia), and toxic ingestions like methanol or ethylene glycol.
Yes — albumin is a major unmeasured anion, so a low albumin lowers the apparent gap. Add about 2.5 mEq/L for each 1 g/dL the albumin is below 4 g/dL.