For healthcare professionals
Delta Ratio (Delta/Delta) Calculator
In a high anion gap metabolic acidosis, the delta ratio compares the rise in the anion gap with the fall in bicarbonate. It can point to a second acid-base disorder alongside the first. This tool is written for clinicians and is not a diagnosis.
Electrolytes
For a metabolic acidosis with an elevated anion gap. Use values from the same sample, in mmol/L. Nothing you enter leaves this page.
What you will see
The anion gap, the delta ratio with the working, and whether the ratio is under 1, 1 to 2, or over 2.
Educational only, not medical advice. Not a diagnosis. Decisions belong to the treating team.
Source
The anion gap and delta ratio equations, the 12 mmol/L anion gap cut-off and the reading of the ratio as printed by Ayala-De la Cruz S and colleagues, Journal of Clinical Medicine 2025, open access (CC BY). The tests check both equations, that a ratio of exactly 1 or 2 counts as 1 to 2, that no ratio is given when the anion gap is not elevated or the bicarbonate is not low, and that a value near a cut-off is never displayed as the cut-off.
Validated in
Ayala-De la Cruz 2025 applied the delta ratio to 200 arterial blood gas results at a single center, using it only for metabolic acidosis with an elevated anion gap.
Limits
The authors note that interpretation of the ratio varies across guidelines and that it should be a supportive tool rather than a standalone diagnostic criterion. Decide first, from the pH and bicarbonate, that a metabolic acidosis is present.
The formulas
Anion gap (AG) = Na - Cl - HCO3 (Ayala-De la Cruz 2025). An anion gap above 12 mmol/L is taken as elevated (Ayala-De la Cruz 2025).
Delta ratio = (AG - 12) / (24 - HCO3) (Ayala-De la Cruz 2025). It is used only for a metabolic acidosis with an elevated anion gap (Ayala-De la Cruz 2025).
Reading the ratio
- 1 to 2: an isolated high anion gap metabolic acidosis (Ayala-De la Cruz 2025).
- Under 1: a high anion gap metabolic acidosis together with a normal anion gap metabolic acidosis (Ayala-De la Cruz 2025).
- Over 2: a high anion gap metabolic acidosis together with a chronic respiratory acidosis or a metabolic alkalosis (Ayala-De la Cruz 2025).
The tool counts a ratio of exactly 1 or 2 as 1 to 2. A value just past a cut-off is shown with extra decimals so it never looks equal to the cut-off.
Worked example: sodium 140, chloride 100 and bicarbonate 12 mmol/L give an anion gap of 28 mmol/L and a delta ratio of (28 - 12) / (24 - 12) = 1.33, in the 1 to 2 range.
Classifying a metabolic acidosis and any associated disorder remains challenging, partly because the ratio is read differently across guidelines (Ayala-De la Cruz 2025).
Related tools
For a normal anion gap acidosis, see the urine anion gap calculator. For the anion gap with the albumin correction, see the anion gap calculator. To check the respiratory response to a metabolic acidosis, use the Winters formula calculator. Other bedside scores are listed under For healthcare professionals.
Sources
- Ayala-De la Cruz S, Arenas-Hernández PE, Fernández-Herrera MF, et al. Human-in-the-loop performance of LLM-assisted arterial blood gas interpretation: a single-center retrospective study. J Clin Med. 2025;14(18):6676. doi:10.3390/jcm14186676. PMID 41010880. Open access (CC BY). Introduction (stepwise evaluation) and Methods: Equation 1 (Winters formula, plus or minus 2 tolerance), Equations 7 and 8 (anion gap, delta ratio), the 12 mmol/L anion gap cut-off and the delta ratio reading; Discussion (the ratio as a supportive tool). pmc.ncbi.nlm.nih.gov/articles/PMC12470526/
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