Delta Ratio Calculator
Enter the anion gap and bicarbonate, adjusting the normal values if needed.
Result
How it is calculated
Anion gap (AG) and bicarbonate (HCO3) are entered in mmol/L. The tool computes delta ratio = (AG − normal AG) ÷ (normal HCO3 − HCO3). The normal values default to 12 for AG and 24 for HCO3 and can be changed to match your lab. The ratio is only defined while bicarbonate is below the normal value; if HCO3 is equal to or above it, or a required field is empty, no result is shown. The ratio is placed in a band: below 0.4, 0.4 to 1, above 1 up to 2, and above 2, each with a one-line interpretation. A value of exactly 1 falls in the 0.4 to 1 band, and an anion gap below normal gives a negative ratio, which lands in the lowest band. The result is an educational aid, not a diagnosis.
Worked example
Suppose AG = 20 mmol/L and HCO3 = 14 mmol/L, with the default normals of 12 and 24. The rise in the anion gap is 20 − 12 = 8. The fall in bicarbonate is 24 − 14 = 10. The delta ratio is 8 ÷ 10 = 0.80. That lies in the 0.4 to 1 band, which the tool describes as suggesting a mixed high anion gap and normal anion gap metabolic acidosis.
Common mistakes
- Typing sodium or chloride into the anion gap box. The tool takes the finished anion gap, which you work out beforehand, and it must be measured the same way as the normal AG you compare it with.
- Putting a bicarbonate at or above the normal (for example 24 or 28) and expecting a ratio. The formula needs bicarbonate below normal, so the tool returns nothing.
- Leaving the normal values at 12 and 24 when your laboratory uses different reference values; change them so both sides of the ratio use the same baseline.
- Reading a ratio of exactly 1.00 as the start of the 1 to 2 band. The tool puts 1.00 in the 0.4 to 1 band, and a rounded 1.00 may really be 0.996 or 1.004.
- Using the ratio alone. It compares two changes and says nothing about the cause, so it is read together with the full blood gas and clinical picture.
About this calculator
The delta ratio (sometimes called delta-delta or ΔAG/ΔHCO3) helps clinicians tell whether a patient’s metabolic acidosis is a pure high-anion-gap process or a mixed disorder: it compares how far the anion gap has risen above normal to how far the bicarbonate has fallen below normal, using Delta ratio = (AG − 12) / (24 − HCO3) with 12 and 24 as the typical normal reference values (adjustable when local lab norms differ).
A ratio above 1 and up to 2 suggests a straightforward high-anion-gap metabolic acidosis (such as diabetic ketoacidosis), a ratio between 0.4 and 1 points toward a mixed high-anion-gap and normal-anion-gap acidosis, a ratio below 0.4 suggests a concurrent normal-anion-gap (hyperchloremic) acidosis, and a ratio above 2 suggests a coexisting metabolic alkalosis or a pre-existing elevated bicarbonate, since the bicarbonate has not fallen as much as the rising anion gap would predict. Physicians and intensive-care clinicians use it alongside arterial blood gas and electrolyte panels to unravel mixed acid-base disorders; enter the anion gap and bicarbonate, adjusting the normal values if your lab uses different reference ranges. Not medical advice.
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