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Renal Emergency Medicine Anaesthesia / Critical Care Standard — widely used ABG interpretation tool

Delta Ratio for Mixed Acid-Base Disorders

The delta ratio (delta anion gap / delta bicarbonate) identifies mixed acid-base disorders in the presence of a high anion gap metabolic acidosis. It reveals whether a concurrent metabolic alkalosis or normal anion gap acidosis is also present.

Score interpretation

Delta Ratio < 0.4 — Normal AG Acidosis Component ≤ 0.4

Delta ratio < 0.4: Bicarbonate has fallen more than the anion gap has risen. Concurrent normal anion gap (hyperchloraemic) acidosis also present.

→ Identify both HAGMA and NAGMA causes. Consider: diarrhoea, RTA, saline infusion alongside DKA, lactic acidosis, uraemia.

Delta Ratio 0.4–0.8 — Mixed HAGMA + NAGMA 0.4–0.8

Delta ratio 0.4–0.8: Suggests mixed high-AG and normal-AG metabolic acidosis.

→ Investigate for combined causes. Typical in early DKA + concurrent diarrhoea or RTA.

Delta Ratio 0.8–2.0 — Pure HAGMA 0.8–2

Delta ratio 0.8–2.0: Pure high anion gap metabolic acidosis. No major concurrent metabolic disorder.

→ Investigate cause of HAGMA: DKA, lactic acidosis, uraemia, toxic alcohols, salicylates.

Delta Ratio > 2.0 — Concurrent Metabolic Alkalosis ≥ 2

Delta ratio > 2.0: Anion gap has risen more than bicarbonate has fallen — a concurrent metabolic alkalosis is present.

→ Identify metabolic alkalosis cause: vomiting, NG suction, loop diuretics, hypokalaemia, exogenous bicarbonate. Common in DKA with persistent vomiting.

Interpretation bands for the Delta Ratio. Apply clinical judgement and local guidance.

References

Related

Curated clinical cross-links plus same-class fallbacks.

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Decision support only — verify against a current formulary, NICE, or your local guideline before clinical use.