What is a corrected anion gap?

The corrected anion gap definition

A corrected anion gap (also called the albumin-corrected AG or adjusted anion gap) is, by definition, the conventional anion gap recalculated for the patient's serum albumin. It is the value you report when a low albumin would otherwise make the raw gap unreadable against the standard 8–12 mEq/L interval. Conceptually it answers: "What would this gap read if the patient's albumin were normal?"

By contrast, the companion FAQ on the albumin effect explains how albumin shifts the gap mechanistically, and our physiology page covers the underlying biochemistry — so we won't re-derive that here. The mathematical adjustment itself is the Figge equation, Corrected AG = Observed AG + 2.5 × (4.0 − albumin g/dL); the full derivation of the 2.5 factor and worked examples at multiple albumin levels are on the corrected anion gap formula page, and the corrected anion gap calculator runs the arithmetic instantly.

When the definition matters in practice

Once you know what a corrected anion gap is, the question is when to use one. The answer: whenever the serum albumin is abnormal, and by default in ICU, cirrhosis, nephrotic syndrome, and severe malnutrition, where albumin < 3.0 g/dL is the rule rather than the exception. For the full clinical when-and-why, including the scenarios where correction most changes management, see why albumin matters.

Key takeaways

• A corrected anion gap is, by definition, the albumin-adjusted anion gap.
• It restores a low-albumin gap to the standard 8–12 mEq/L reference frame.
• Use it whenever albumin is abnormal — especially < 3.0 g/dL.
• For the formula derivation and the mechanism, see the linked pages above.