Clinical Overview
The Delta Ratio (or Delta-Delta gap) is an advanced acid-base calculation used in critical care. It is calculated only when a high anion gap metabolic acidosis is already confirmed. It helps uncover hidden, simultaneous acid-base derangements.
Pathophysiology & Evidence
Theoretically, for every 1 mEq/L increase in unmeasured anions (the anion gap), the bicarbonate should decrease by exactly 1 mEq/L as it acts as a buffer.
- If the ratio is between 1 and 2, it's a pure high anion gap acidosis.
- If the ratio is > 2, the bicarbonate is higher than expected, revealing a hidden concomitant metabolic alkalosis (e.g., a vomiting patient with DKA).
- If the ratio is < 0.8, the bicarbonate is lower than expected, revealing a hidden normal anion gap acidosis (e.g., DKA with concurrent severe diarrhea).
Formula Breakdown
Delta Ratio = (Measured AG - Normal AG) / (Normal HCO3 - Measured HCO3)