Delta Gap

Name: Delta Gap calculator — MedScore
Creator: Nabil Alzein

Compares the rise in the anion gap with the fall in bicarbonate to look for a mixed acid–base disorder

Sodium (mmol/L)

Chloride (mmol/L)

Bicarbonate (mmol/L)

Albumin (g/dL) — optional, for correction

Enter sodium, chloride, and bicarbonate to calculate

About this score

When to use

Compares the rise in the anion gap with the fall in bicarbonate (ΔAG − ΔHCO₃⁻) to look for a second acid–base disorder next to a high-gap metabolic acidosis. ⁦[1]⁩

Pearls and pitfalls

• Above +6 usually means a concurrent metabolic alkalosis; below −6 a concurrent hyperchloraemic (normal-gap) acidosis. ⁦[1]⁩

• The ΔAG/ΔHCO₃⁻ ratio is close to 1 on average but varies widely between patients, so it should be used cautiously to diagnose a mixed disorder. ⁦[2]⁩

Summarised from the numbered sources under Evidence. Check the source before relying on a statement.

Evidence

[1] Original publication

Wrenn K. The delta (delta) gap: an approach to mixed acid-base disorders. Defines the delta gap as ΔAG − ΔHCO₃⁻: significantly positive (> +6) usually means a concurrent metabolic alkalosis, significantly negative (< −6) a concurrent hyperchloraemic acidosis.

Annals of Emergency Medicine, 1990

Open source

[2] Validation

Rastegar A. Use of the ΔAG/ΔHCO₃⁻ ratio in the diagnosis of mixed acid-base disorders. The ratio is expected to be close to unity when a strong acid is added to plasma, but has a wide range in individual patients, so it should be used cautiously to diagnose a mixed disorder (shown here for information only).

Journal of the American Society of Nephrology, 2007

Open source

[3] Guideline

Kraut JA, Madias NE. Treatment of acute metabolic acidosis: a pathophysiologic approach. Calculating the serum anion gap and its change from baseline helps detect organic acidoses. The anion gap itself (and the albumin correction) is the one from the Anion Gap calculator.

Nature Reviews Nephrology, 2012

Open source

Last reviewed: 2026-10

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MedScore is an educational and clinical decision-support tool. It does not provide a diagnosis, a treatment, or a drug-dosing recommendation, and it does not replace clinical judgement or local guidelines. Confirm every result against the original source before acting on it. The treating clinician remains responsible for all decisions.