Delta Ratio Calculator (Delta-Delta Gap)
Calculate the delta ratio (ΔAG/ΔHCO₃⁻), delta gap and corrected bicarbonate from sodium, chloride, bicarbonate and albumin to spot mixed acid-base disorders in a high anion gap acidosis.
How it works
AG = Na⁺ − (Cl⁻ + HCO₃⁻) · albumin-corrected AG = AG + 2.5 × (4.0 − albumin g/dL) · ΔAG = AG − normal AG (12) · ΔHCO₃⁻ = normal HCO₃⁻ (24) − HCO₃⁻ · delta ratio = ΔAG ÷ ΔHCO₃⁻ · corrected HCO₃⁻ = HCO₃⁻ + ΔAG
In a pure high anion gap metabolic acidosis, each unmeasured acid anion that raises the anion gap consumes about one bicarbonate, so the rise in the gap and the fall in bicarbonate should be similar and their ratio close to 1–2. A ratio below 0.8 means bicarbonate has fallen more than the gap explains, so a second, normal anion gap (hyperchloremic) acidosis is present; a ratio above 2 means bicarbonate is higher than expected, pointing to a coexisting metabolic alkalosis (for example from vomiting) or a compensated chronic respiratory acidosis. Bands follow Rastegar (J Am Soc Nephrol 2007); the gap is corrected for low albumin with the Figge factor of 2.5 mmol/L per 1 g/dL.
Worked example
Sodium 140, chloride 100 and bicarbonate 10 mmol/L with albumin 40 g/L (4.0 g/dL, so no albumin correction): anion gap = 140 − 110 = 30 mmol/L. ΔAG = 30 − 12 = 18 and ΔHCO₃⁻ = 24 − 10 = 14, so the delta ratio is 18 ÷ 14 = 1.29 — a pure high anion gap metabolic acidosis. The corrected bicarbonate is 10 + 18 = 28 mmol/L, within the normal range.
Sources: Rastegar A. Use of the ΔAG/ΔHCO₃⁻ ratio in the diagnosis of mixed acid-base disorders. J Am Soc Nephrol 2007;18:2429–31 · Figge J et al. Anion gap and hypoalbuminemia. Crit Care Med 1998;26:1807–10
Frequently asked questions
What is a normal delta ratio?
In an uncomplicated high anion gap metabolic acidosis the delta ratio is usually between 1 and 2 (around 1.6 in lactic acidosis, because lactate is cleared more slowly than hydrogen ions are buffered, and closer to 1 in DKA, because ketones are lost in the urine).
What does a delta ratio below 1 mean?
Bicarbonate has fallen more than the anion gap has risen. Between 0.4 and 0.8 it suggests a combined high anion gap and normal anion gap (hyperchloremic) acidosis, for example DKA treated with lots of saline or diarrhoea plus lactic acidosis; below 0.4 the acidosis is mainly hyperchloremic.
What does a delta ratio above 2 mean?
Bicarbonate is higher than the anion gap would predict, so there is extra alkali: a concurrent metabolic alkalosis (vomiting, diuretics, nasogastric suction) or a pre-existing compensated respiratory acidosis with a raised baseline bicarbonate.
What is the difference between the delta ratio and the delta gap?
They use the same numbers. The delta ratio divides ΔAG by ΔHCO₃⁻; the delta gap subtracts them (ΔAG − ΔHCO₃⁻). A delta gap above about +6 suggests metabolic alkalosis and below about −6 a normal anion gap acidosis. Adding ΔAG back to the measured bicarbonate gives the “corrected bicarbonate”: above 30 mmol/L suggests alkalosis, below 23 a hyperchloremic acidosis.
Should I correct the anion gap for albumin?
Yes, when albumin is low. Albumin is the main unmeasured anion, so each 1 g/dL (10 g/L) fall below 4 g/dL lowers the gap by about 2.5 mmol/L and can hide a high anion gap acidosis.
Related calculators
Educational calculation only, not medical advice or a diagnosis. Reference ranges and units differ between laboratories; interpret any result with your doctor in the context of your full clinical picture.