The delta ratio is a formula that can be used to assess high anion gap metabolic acidosis and to evaluate whether a mixed acid-based disorder is present.
Delta ratio = Delta anion gap/Delta HCO3- = [AG -12] ÷ [24 - HCO3-]
The ratio gives one of four results, presented in the table below.
Delta Ratio |
Assessment |
Less than 0.4 |
A normal anion gap metabolic acidosis (i.e., hyperchloremia) |
0.4-1 |
A mixed non-anion gap metabolic acidosis and a high-anion gap metabolic acidosis in which both renal function is preserved and the acid anion is readily excreted into the urine (i.e., ketoacidosis, toluene ingestion, or D-lactic acidosis) |
1-2 |
An uncomplicated high anion gap metabolic acidosis, also called a “pure high anion gap metabolic acidosis” |
Greater than 2 |
Due to a mixed high anion gap metabolic acidosis and an alkalosis (pre-existing elevated HCO3- [metabolic alkalosis or respiratory acidosis] or that the baseline HCO3- level is elevated as a result of chronic respiratory acidosis) |
Reference:
Rastegar, A. (2007). Use of Delta AG/DeltaHCO3- Ratio in the Diagnosis of Mixed Acid-Base Disorders. Journal of the American Society of Nephrology, 18.9 (2429-2431).
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