In diabetic ketoacidosis, the anion gap is elevated because of accumulation of ketoacid anions. The anion gap is calculated as Na+ − (Cl− + HCO3−). A patient has Na+ 140, Cl− 112, HCO3− 8 mEq/L. What is the anion gap and what does a simultaneous delta ratio (delta gap / delta bicarbonate) of 0.5 suggest?

• A AG = 20; delta ratio of 0.5 suggests a superimposed normal anion gap (hyperchloraemic) metabolic acidosis in addition to the high-AG acidosis ✓
• B AG = 20; delta ratio of 0.5 suggests pure high-AG metabolic acidosis
• C AG = 20; delta ratio of 0.5 suggests a concurrent metabolic alkalosis
• D AG = 20; delta ratio of 0.5 is within normal range and no additional disorder is present

Explanation

AG = 140 − (112 + 8) = 20 mEq/L (elevated; normal ~12 ± 2). Delta gap = 20 − 12 = 8; delta bicarbonate = 24 − 8 = 16; delta ratio = 8/16 = 0.5. A delta ratio < 1 means HCO3− has fallen more than the rise in anion gap, indicating a concurrent normal anion gap (hyperchloraemic) metabolic acidosis superimposed on the high-AG ketoacidosis — consistent with the elevated chloride here. Interpretation guide: delta ratio 1–2 = pure high-AG metabolic acidosis; >2 = concurrent metabolic alkalosis (or pre-existing high HCO3−); <1 = concurrent normal-AG acidosis.

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

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