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.
|Less than 0.4
||A normal anion gap metabolic acidosis (i.e., hyperchloremia)
||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)
||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)
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).