Anion Gap Delta Ratio Calculator

Compare how far the anion gap has risen with how far bicarbonate has fallen — the quickest way to spot a second, hidden metabolic process.

Sodium (mmol/L):

Chloride (mmol/L):

Bicarbonate (mmol/L):

Albumin (g/dL):

Reference anion gap (mmol/L):

Delta ratio

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Anion gap (corrected)

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Measured anion gap: — mmol/L

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What the Delta Ratio Detects

A high anion gap metabolic acidosis should lower bicarbonate roughly in proportion to the rise in the anion gap, because the accumulating acid consumes bicarbonate one-for-one. When the two changes do not match, a second process is present — another acidosis, or a metabolic alkalosis pulling bicarbonate back up. The delta ratio (also called the delta-delta) quantifies that mismatch.

The Formulas

Anion gap = sodium − (chloride + bicarbonate)
Corrected anion gap = anion gap + 2.5 × (4.0 − albumin in g/dL)
ΔAG = corrected anion gap − reference anion gap
ΔHCO₃ = 24 − measured bicarbonate
Delta ratio = ΔAG ÷ ΔHCO₃

Reading the Ratio

Below 0.4 — predominantly normal anion gap (hyperchloraemic) acidosis: the bicarbonate fell but the anion gap barely moved
0.4 to 0.8 — mixed high and normal anion gap acidosis
0.8 to 2.0 — pure high anion gap metabolic acidosis, the expected pattern
Above 2.0 — high anion gap acidosis with a coexisting metabolic alkalosis (vomiting, diuretics) or a chronic respiratory acidosis

Two worked examples. In diabetic ketoacidosis with an anion gap of 30 and bicarbonate of 10, ΔAG is 18 and ΔHCO₃ is 14, giving a ratio of 1.29 — a pure high anion gap acidosis. Add profuse vomiting to the same patient and bicarbonate might sit at 20 instead: ΔAG 18 divided by ΔHCO₃ 4 gives 4.5, revealing the superimposed metabolic alkalosis.

Why the Albumin Correction Matters Here

Albumin is the main unmeasured anion. When it is low — as it often is in chronic illness, sepsis and liver disease — the measured anion gap underestimates the true unmeasured anion load. Because the delta ratio depends on the anion gap, using an uncorrected value in a hypoalbuminaemic patient systematically pushes the ratio downwards and can mask a high anion gap acidosis. This calculator applies the correction before computing ΔAG.

Limitations

The reference anion gap varies between laboratories, typically 8–12 mmol/L; changing it shifts the ratio substantially, which is why the value used is shown and selectable.
It assumes a steady state. During rapid evolution or treatment of ketoacidosis, bicarbonate and the anion gap move at different speeds and the ratio can mislead.
Other unmeasured anions are ignored. Potassium, calcium, magnesium and paraproteins all affect the gap.
Chronic respiratory disorders alter baseline bicarbonate and therefore the denominator.
It describes acid-base physiology only and says nothing about the cause, which still requires the clinical picture and specific tests.

Clinical Reference Only This calculator is intended for educational and clinical reference purposes by healthcare professionals and students. It does not diagnose any condition and must be interpreted alongside the full blood gas, electrolytes and clinical assessment.

Frequently Asked Questions

Is the delta ratio the same as the delta gap?

Closely related. The delta gap is simply ΔAG − ΔHCO₃; the delta ratio divides one by the other, which makes it comparable between patients with different degrees of acidosis.

What if bicarbonate is normal or high?

Then there is no metabolic acidosis to compare against and the ratio is not interpretable. In that situation assess the anion gap and the clinical context directly.

My patient has a ratio of 0.6 — what does that mean at the bedside?

It suggests two acidoses running together, typically a high anion gap process plus a hyperchloraemic one from saline, diarrhoea or renal tubular acidosis. Look for both rather than settling on the first explanation.