Delta Gap Calculator

About the Delta Gap Calculator

In a pure high anion gap metabolic acidosis, each unmeasured acid that accumulates consumes roughly one bicarbonate ion, so the rise in the anion gap (ΔAG) and the fall in bicarbonate (ΔHCO₃⁻) should be similar. The delta gap calculations compare the two. When bicarbonate has fallen much more than the gap has risen, a second, normal anion gap (hyperchloraemic) acidosis is likely; when bicarbonate has fallen much less, a coexisting metabolic alkalosis is likely.

Enter sodium, chloride and bicarbonate from the same sample. Add albumin to correct the anion gap (each 1 g/dL below 4.0 lowers the gap by about 2.5 mEq/L), and adjust the normal anion gap and normal bicarbonate if your laboratory uses different reference values. The calculator shows the anion gap, the delta ratio (ΔAG ÷ ΔHCO₃⁻), the delta-delta difference (ΔAG − ΔHCO₃⁻) and the “corrected” bicarbonate — the value bicarbonate would have if the high-gap acidosis were removed.

The delta ratio is only meaningful when there is a raised anion gap and a low bicarbonate. Interpretation bands are rules of thumb with real overlap: diabetic ketoacidosis often gives a ratio near 1 because ketoanions are lost in urine, while in lactic acidosis the rise in the gap often exceeds the fall in bicarbonate, giving a ratio above 1. The tool supports, but does not replace, a full clinical acid–base assessment.

With the default inputs, the delta ratio (δag ÷ δhco₃⁻) is 1.4. Change any value above to recalculate instantly.

How to use the delta gap calculator

1Enter sodium, chloride and bicarbonate from the same blood sample.
2Enter serum albumin if available to correct the anion gap.
3Adjust the normal anion gap and bicarbonate to your lab’s values if needed.
4Read the delta ratio, then check the delta-delta and corrected bicarbonate.

Formula and method

AG = Na⁺ − (Cl⁻ + HCO₃⁻) [+ 2.5 × (4 − albumin)] · ΔAG = AG − 12 · ΔHCO₃⁻ = 24 − HCO₃⁻ · Delta ratio = ΔAG ÷ ΔHCO₃⁻ · Delta-delta = ΔAG − ΔHCO₃⁻

The anion gap is calculated without potassium and optionally corrected for albumin. ΔAG is how far the gap sits above normal (default 12 mEq/L) and ΔHCO₃⁻ is how far bicarbonate sits below normal (default 24 mEq/L). In a pure high-gap acidosis the two change roughly one-for-one, so the ratio is about 1–2 (above 1 because some acid is buffered inside cells and bone).

A ratio below 0.4 points to a predominantly hyperchloraemic normal-gap acidosis; 0.4–1 suggests a combined high-gap and normal-gap acidosis; above 2 suggests a coexisting metabolic alkalosis or a compensated chronic respiratory acidosis. The delta-delta difference and corrected bicarbonate (HCO₃⁻ + ΔAG) express the same comparison in mEq/L.

AG: Anion gap (mEq/L)
ΔAG: Rise in anion gap above normal
ΔHCO₃⁻: Fall in bicarbonate below normal

Worked examples

Pure high anion gap acidosis

AG = 140 − (100 + 14) = 26, so ΔAG = 14. Bicarbonate has fallen by 24 − 14 = 10. The ratio 14 ÷ 10 = 1.4 fits a pure high anion gap acidosis such as lactic acidosis.

Mostly hyperchloraemic acidosis

AG = 138 − 122 = 16, only 4 above normal, while bicarbonate has fallen by 12. The ratio of 0.33 shows the fall in bicarbonate is mostly due to a normal-gap process such as diarrhoea or renal tubular acidosis.

Acidosis hiding a metabolic alkalosis

The raw gap is 30; with albumin 3 g/dL it corrects to 32.5, so ΔAG = 20.5 while bicarbonate fell only 4. The ratio of about 5.1 and corrected bicarbonate of 40.5 point to a coexisting metabolic alkalosis, for example from vomiting.

Frequently asked questions

What is the delta gap?+

The delta gap compares the increase in the anion gap with the decrease in bicarbonate. It is expressed either as a ratio (delta ratio) or a difference (delta-delta), and helps reveal a second metabolic disorder hidden behind a high anion gap acidosis.

What is a normal delta ratio?+

In an uncomplicated high anion gap metabolic acidosis the delta ratio is usually between 1 and 2. Lactic acidosis often runs well above 1, while diabetic ketoacidosis tends to be closer to 1 because ketoanions are lost in the urine.

What does a delta ratio above 2 mean?+

Bicarbonate is higher than expected for the size of the anion gap, which suggests a coexisting metabolic alkalosis (such as from vomiting or diuretics) or a pre-existing compensated chronic respiratory acidosis.

What does a delta ratio below 1 mean?+

Bicarbonate has fallen more than the anion gap explains, suggesting an additional normal anion gap acidosis. Below 0.4 the normal-gap (hyperchloraemic) component usually dominates, as with diarrhoea or renal tubular acidosis.

Should I correct the anion gap for albumin first?+

Yes, when albumin is low. Albumin is the main unmeasured anion, and hypoalbuminaemia lowers the gap by about 2.3–2.5 mEq/L per 1 g/dL fall (this calculator uses 2.5). Without correction the ΔAG, and therefore the delta ratio, is underestimated.

For healthcare professionals and education only. This calculator implements a published formula or score but is not a diagnosis and does not replace clinical judgment. Verify inputs and results against the original source before using them in patient care.

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