The delta-delta ratio (delta AG / delta HCO3-) is used to detect a concurrent metabolic alkalosis in a high anion gap metabolic acidosis. A delta-delta ratio >2 suggests:

• A A concurrent metabolic alkalosis (HCO3- is higher than expected for the AG rise) ✓
• B A concurrent non-anion gap metabolic acidosis
• C Adequate respiratory compensation
• D A pure high anion gap metabolic acidosis

Explanation

Delta ratio = (AG − 12) / (24 − HCO3-); in pure HAGMA the ratio is 1–2 (AG rise approximates HCO3- fall). A ratio >2 means the AG has risen more than the HCO3- has fallen, indicating that HCO3- is protected by a co-existing metabolic alkalosis. A ratio <1 indicates a concurrent normal anion gap metabolic acidosis adding to the HCO3- loss. This is a key clinical discriminator in mixed acid-base disorders.

Reference: Harper's Illustrated Biochemistry, 32nd ed.

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Written and medically reviewed by the StethoPrep medical team.