Albumin-Corrected AG
The Albumin Corrected Anion Gap Calculator adjusts a measured anion gap for low serum albumin, since hypoalbuminaemia lowers the anion gap and can mask an underlying high-anion-gap metabolic acidosis. It applies AG + 2.5 × (Normal − Measured Albumin) when albumin is in g/dL, or the equivalent AG + 0.25 × (Normal − Measured) in g/L. The app attributes the original derivation of this correction factor to Figge et al., Critical Care Medicine 1998.
The app explains that albumin is the dominant unmeasured anion contributing to a normal anion gap, so for every 1 g/dL drop in albumin, the measured AG falls by approximately 2.5 mEq/L.
AG + 2.5 × (Normal Albumin − Measured Albumin) when albumin is entered in g/dL, or AG + 0.25 × (Normal − Measured) when entered in g/L.
The calculator defaults to a normal albumin of 4.0 g/dL (or 40 g/L), which can be adjusted.
The app notes this is particularly relevant for critically ill or nephrotic patients, where the raw measured AG can mask a true high-anion-gap metabolic acidosis.
The app cites the original derivation to Figge J, Critical Care Medicine 1998.