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Delta Gap and Delta Ratio

The delta ratio (ΔAG ÷ ΔHCO₃, with AG normal 12 and HCO₃ normal 24) detects mixed disorders in a high-anion-gap acidosis: <0.4 normal-gap acidosis, 0.4–0.8 combined high- and normal-gap acidosis, 0.8–2 pure high-gap acidosis, >2 concurrent metabolic alkalosis (or chronic respiratory acidosis).

Serum sodium (mmol/L or mEq/L)
Serum chloride (mmol/L or mEq/L)
Serum bicarbonate (HCO₃⁻) (mmol/L or mEq/L)
Serum albumin (g/dL or g/L)

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Interpretation

Result	Meaning
< 0.4	Normal-gap acidosis
0.4–0.8	Mixed high-gap + normal-gap acidosis
0.8–2.0	Pure high-gap acidosis
> 2.0	High-gap acidosis + metabolic alkalosis or chronic respiratory acidosis

Formula

Delta ratio = (AG − 12) ÷ (24 − HCO₃⁻). Delta gap = (AG − 12) − (24 − HCO₃⁻). AG = Na⁺ − (Cl⁻ + HCO₃⁻), optionally + 2.5 × (4 − albumin g/dL).

Clinical pearls

Use the same "normal" anion gap your lab uses; with a normal AG of ~8 the ratio shifts.
The ratio is unreliable when ΔHCO₃ is small (mild acidosis); interpret with pH, pCO₂ and clinical context.

Examples

delta ratio na 140 cl 100 hco3 10 delta delta 138 cl 95 bicarb 20 is there a mixed disorder: sodium 140, chloride 110, bicarbonate 12

FAQ

What does a delta ratio above 2 mean?

The bicarbonate is higher than expected for the anion gap rise, suggesting a concurrent metabolic alkalosis (e.g. vomiting) or a pre-existing compensated respiratory acidosis.

What is the difference between delta gap and delta ratio?

The delta gap is ΔAG − ΔHCO₃ (near 0 in pure gap acidosis); the delta ratio is ΔAG ÷ ΔHCO₃ (about 1–2 in pure gap acidosis).

Evidence

Rastegar A. Use of the ΔAG/ΔHCO3− ratio in the diagnosis of mixed acid-base disorders. J Am Soc Nephrol 2007;18:2429–31.

Nephrology & Electrolytes · Reviewed 2026-10-14 · Methodology