Acid Base Learner Series: The Delta Ratio

Definition

This Delta Ratio is sometimes useful in the assessment of metabolic acidosis. As this concept is related to the anion gap (AG) and buffering, it will be discussed here before a discussion of metabolic acidosis. The Delta Ratio is defined as:

Delta ratio = (Increase in Anion Gap / Decrease in bicarbonate)

Others have used the delta gap (defined as rise in AG minus the fall in bicarbonate), but this uses the same information as the delta ratio and has does not offer any advantage over it.

How is this useful?

In order to understand this, consider the following:
If one molecule of metabolic acid (HA) is added to the ECF and dissociates, the one H⁺ released will react with one molecule of HCO₃^- to produce CO₂ and H₂O. This is the process of buffering. The net effect will be an increase in unmeasured anions by the one acid anion A^- (ie anion gap increases by one) and a decrease in the bicarbonate by one.
Now, if all the acid dissociated in the ECF and all the buffering was by bicarbonate, then the increase in the AG should be equal to the decrease in bicarbonate so the