Anion Gap and Delta Ratio Calculator
Anion gap corrected for albumin (Figge) and the ΔAG/ΔHCO₃ delta ratio to distinguish high- and normal-anion-gap acidosis.
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Calculation
Result
- Albumin-corrected anion gap
- 12.0 mmol/L
- Interpretation
- Within the assumed 8–12 mmol/L range
- Uncorrected anion gap
- 12.0 mmol/L
- Delta ratio (ΔAG / ΔHCO₃)
- not applicable
This calculation uses 8–12 mmol/L without potassium. Check your laboratory reference interval.
Na − (Cl + HCO₃); equals the corrected gap at normal albumin
Calculated only when the anion gap is elevated and bicarbonate reduced
Albumin correction — Figge 1998; interpretation — Kraut & Madias 2007, Berend 2014. Reference ranges are population benchmarks from the cited sources. Laboratories use their own ranges, and interpretation depends on clinical context: discuss the result with your physician.
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How it is calculated
The anion gap is the difference between measured serum cations and anions, reflecting "unmeasured" anions: phosphates, sulfates, organic acids and negatively charged albumin. In metabolic acidosis it rises if acids accumulate (lactate, ketones, uremic toxins, toxic alcohols) and stays normal if bicarbonate is lost (diarrhea, renal tubular acidosis) and replaced by chloride. Since albumin is the main unmeasured anion, hypoalbuminemia falsely lowers the gap: Figge (1998) proposed a correction of 2.5 mmol/L per 1 g/dL fall in albumin. The delta ratio compares the rise in the gap with the fall in bicarbonate and reveals mixed disorders.
Formula
AG = Na − (Cl + HCO₃), mmol/L, without potassium. Figge adjustment: AG + 0.25 × (40 − albumin, g/L). Delta ratio = (adjusted AG − 12) / (24 − HCO₃). Calculated only if AG > 12 and HCO₃ < 24. Delta-ratio bands suggest possible mixed disturbances; they are not diagnoses.
Limits of the method
The anion gap reference depends on the analyzer: modern ion-selective electrodes give 3–11 mmol/L, older methods 8–16. Check your lab’s reference. The calculation excludes potassium; if your lab includes it, the reference is 4–5 higher. The delta ratio is a rough guide that needs context (pH, pCO₂, lactate, ketones). The calculator is meant for interpretation of acid-base disorders by professionals and does not replace blood gas analysis.
Sources of the method
- Kraut J.A., Madias N.E. Serum anion gap: its uses and limitations in clinical medicine. Clin J Am Soc Nephrol, 2007;2(1):162–174
- Figge J., Jabor A., Kazda A., Fencl V. Anion gap and hypoalbuminemia. Crit Care Med, 1998;26(11):1807–1810
- Berend K., de Vries A.P., Gans R.O. Physiological approach to assessment of acid-base disturbances. N Engl J Med, 2014;371(15):1434–1445
This calculation is for reference only and is not medical advice, a diagnosis or a prescription. If you have a medical condition, are pregnant, take medication or have any doubts, discuss the result with a physician or a qualified nutrition professional.
How to calculate the anion gap
Take electrolytes from one sample
Sodium, chloride and bicarbonate (or total CO₂) must come from one draw, ideally alongside blood gases. Different samples give a meaningless gap.
Add albumin
In ICU patients, cirrhosis, nephrotic syndrome and wasting albumin is often 20–30 g/L: without correction a high anion gap masquerades as normal.
Interpret the delta ratio in context
The delta ratio helps spot a second disorder (bicarbonate loss or alkalosis) behind a high-AG acidosis, but needs pH, lactate and the clinical picture.
Anion gap worked examples
Na 140, Cl 104, HCO₃ 24, albumin 40 g/L
Gap 12 mmol/L, no correction needed, bicarbonate normal — no acid-base disturbance by these data.
Na 138, Cl 100, HCO₃ 14, albumin 40 g/L
Gap 24 at bicarbonate 14: delta ratio (24 − 12)/(24 − 14) = 1.2 — pure high-anion-gap acidosis. Typical of ketoacidosis or lactic acidosis.
Na 136, Cl 108, HCO₃ 15, albumin 28 g/L
Uncorrected, a gap of 13 looks almost normal, but at albumin 28 g/L the corrected gap is 16. Delta ratio 0.44: mixed acidosis — high AG plus a hyperchloremic component.
What hides behind a high anion gap
The GOLD MARK mnemonic: glycols (ethylene, propylene), oxoproline (acetaminophen), L-lactate, D-lactate (short bowel syndrome), methanol, aspirin, renal failure, ketoacidosis (diabetic, alcoholic, starvation). In nutrition practice the most relevant are ketoacidosis on strict ketogenic diets and fasting, lactic acidosis on metformin with CKD, and "euglycemic" ketoacidosis on SGLT2 inhibitors combined with low-carbohydrate eating.
Normal-anion-gap acidosis: no less important
If bicarbonate is lost rather than "consumed" by acids, the gap does not rise: chloride takes bicarbonate’s place. Causes — diarrhea, intestinal fistulas, ureterosigmoidostomy, renal tubular acidosis, carbonic anhydrase inhibitors, large-volume saline infusions. The urine anion gap helps separate renal from extrarenal causes: negative (Cl > Na + K) points to GI losses, positive to renal tubular acidosis.
Interpreting the anion gap and delta ratio
| Marker | Value | Interpretation |
|---|---|---|
| Corrected AG | 8–12 mmol/L | Assumed range; pH and blood gases are needed to assess acidosis |
| Corrected AG | > 12 mmol/L | Elevated index: the cause requires separate assessment |
| Delta ratio | < 0.4 / 0.4–0.8 | Hyperchloremic acidosis predominates or is added (HCO₃ loss) |
| Delta ratio | 0.8–2.0 / > 2.0 | May be consistent with high-gap acidosis / a mixed process is possible |
The AG reference depends on the analyzer; with potassium in the formula normal is 4–5 mmol/L higher.
Frequently asked questions
What is a normal anion gap?
Classically 8–12 mmol/L without potassium and 12–16 with it. Modern ion-selective analyzers measure chloride more accurately, and their normal is lower — 3–11 mmol/L. Go by your lab’s reference.
Why correct for albumin?
Albumin carries negative charge and makes up most of the unmeasured anions. For every 1 g/dL (10 g/L) fall, the gap drops by about 2.5 mmol/L, and a high anion gap in acidosis can look normal.
Can a keto diet raise the anion gap?
Moderate nutritional ketosis gives ketones of 0.5–3 mmol/L and a slight rise in the gap without acidosis. Dangerous ketoacidosis on a keto diet has been described in diabetes, pregnancy, breastfeeding, fasting and with SGLT2 inhibitors — in these groups electrolyte monitoring is mandatory.
What does a low anion gap mean?
Most often hypoalbuminemia or a lab error. Less often — paraproteinemia (myeloma, IgG is a cationic protein), hypercalcemia, hypermagnesemia, lithium or bromide intoxication.
What is the delta ratio?
The ratio of the rise in anion gap to the fall in bicarbonate. In pure high-AG acidosis each mmol of accumulated acid "consumes" about 1 mmol of bicarbonate (ratio 1–2). Deviations point to a second disorder: bicarbonate loss (< 0.8) or alkalosis (> 2).
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What next
Formula breakdowns, biomarker reference ranges and nutrition articles with cited sources are in the NutriFit knowledge base.
Go to the knowledge base