A delta-delta ratio greater than 2 indicates what?

• A. Concurrent non-anion gap metabolic acidosis
• B. Pure high anion gap metabolic acidosis
• C. Normal anion gap metabolic acidosis
• D. Concurrent metabolic alkalosis

Answer: (D)

The delta-delta ratio is used to detect a second acid-base disturbance when there is a high anion gap metabolic acidosis. It compares how much the anion gap has increased (measured AG minus normal AG, about 12) to how much the bicarbonate has fallen (normal HCO3 minus measured HCO3, about 24 minus the bicarbonate). If this ratio is around 1, the changes fit a single high anion gap acidosis. If the ratio is greater than about 2, there is an additional alkali gain — a concurrent metabolic alkalosis — atop the high anion gap acidosis. Thus, a delta-delta ratio greater than 2 points to concurrent metabolic alkalosis.