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Delta Gap & Delta Ratio Calculator

Delta gap and delta ratio to look for mixed acid–base disorders in high anion gap acidosis.

For healthcare professionalsElectrolytes & laboratoryv1.0.1

For healthcare professionals / clinical use. Not a self-diagnosis tool.

Your measurements

mmol/L
mmol/L
mmol/L

Calculated on your device. Nothing is sent to a server.

Your result will appear here

Enter your measurements, then press Calculate.

Methodology

Delta ratio (Rastegar 2007)

Δratio = (AG − 12) ÷ (24 − HCO₃)

Compares the rise in anion gap with the fall in bicarbonate, assuming normal values of 12 and 24 mmol/L. The bands are common teaching ranges, not validated diagnostic cut-offs.

Who it is for
Adults with a raised anion gap metabolic acidosis.
Version
1.0.1

How this calculator works

Where the formula comes from

  • Rastegar (2007) explains that adding a strong acid should raise the anion gap about as much as bicarbonate falls, so a ratio near 1 suggests a pure high anion gap acidosis.[1]

The inputs

  • The anion gap is sodium minus (chloride + bicarbonate); its normal value varies widely with measurement methods and between individuals.[2]

Where accuracy falls (published evidence)

  • Although the mean ratio in selected patients is close to 1, it has a wide range, so it should be used cautiously to diagnose mixed disorders in individual patients.[1]
  • In a study of diabetic ketoacidosis, ratio limits of 0.8 and 1.2 overdiagnosed mixed disorders; a difference of more than 8 mEq/L between the anion gap rise and bicarbonate fall was more accurate.[3]
  • Variability in the ratio undercuts its use alone to detect complex acid–base disorders; other clinical information is needed.[2]

Sources

  1. Rastegar A. Use of the ΔAG/ΔHCO3− ratio in the diagnosis of mixed acid-base disorders. J Am Soc Nephrol. 2007;18(9):2429–2431. doi:10.1681/ASN.2006121408
  2. Kraut JA, Madias NE. Serum anion gap: its uses and limitations in clinical medicine. Clin J Am Soc Nephrol. 2007;2(1):162–174. doi:10.2215/CJN.03020906
  3. Paulson WD, Gadallah MF. Diagnosis of mixed acid-base disorders in diabetic ketoacidosis. Am J Med Sci. 1993;306(5):295–300. doi:10.1097/00000441-199311000-00004

Compiled from the published sources above. Every statement was agreed independently by three AI research tools (Claude, ChatGPT, DeepSeek) and its source verified in PubMed or Crossref by the Hakeemly editorial team. Not reviewed by a doctor unless stated. Agreed on

Worked example: how to calculate delta ratio

Inputs

Sodium
140 mmol/L
Chloride
100 mmol/L
Bicarbonate (HCO₃⁻)
12 mmol/L

Result

Delta ratio (ΔAG / ΔHCO₃)
1.33
Delta gap ((AG − 12) − (24 − HCO₃))
4 mmol/L
Anion gap used
28 mmol/L

0.8–2.0: consistent with a pure high anion gap acidosis

Calculation:

AG 28; (28−12)/(24−12) = 1.33

An illustration with sample values, worked out with the same method the tool above uses.

Limitations

  • Assumed normal values vary between patients and laboratories; interpret with blood gases and the clinical picture.
  • The ratio varies widely between patients; use it cautiously (Rastegar 2007).

References

  1. Rastegar A. Use of the ΔAG/ΔHCO3− ratio in the diagnosis of mixed acid-base disorders. J Am Soc Nephrol. 2007;18(9):2429–2431. doi:10.1681/ASN.2006121408
  2. Kraut JA, Madias NE. Serum anion gap: its uses and limitations in clinical medicine. Clin J Am Soc Nephrol. 2007;2(1):162–174. doi:10.2215/CJN.03020906

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