Anion Gap Calculator
Calculate serum anion gap and albumin-corrected anion gap for metabolic acidosis diagnosis.
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How to use this calculator
The anion gap represents unmeasured anions in plasma. A corrected value accounts for hypoalbuminaemia, which artificially lowers the gap and can mask a true elevated anion gap acidosis.
- 1
Enter serum sodium, chloride, and bicarbonate values from a basic metabolic panel.
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Enter the serum albumin level (default is 4.0 g/dL for normal patients).
- 3
Review the calculated anion gap and albumin-corrected gap.
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An AG above 12 mEq/L warrants investigation for elevated anion gap metabolic acidosis.
Frequently asked questions
What causes an elevated anion gap?
The mnemonic MUDPILES covers common causes: Methanol, Uraemia, Diabetic ketoacidosis, Propylene glycol, Isoniazid/Iron, Lactic acidosis, Ethylene glycol, and Salicylates.
Why correct for albumin?
Albumin is a negatively charged protein that contributes to the anion gap. Low albumin (common in critically ill patients) artificially lowers the AG, potentially hiding a true elevated-AG acidosis. Each 1 g/dL drop in albumin reduces the AG by ~2.5 mEq/L.
What is the normal anion gap range?
The traditional normal range is 8–12 mEq/L. With modern ion-specific electrodes, some labs use a lower range of 6–10 mEq/L. Always compare against your laboratory's reference range.
What is a normal anion gap acidosis?
When acidosis is present with a normal anion gap, it suggests causes such as diarrhoea, renal tubular acidosis, or excessive normal saline administration — conditions that cause hyperchloraemia rather than accumulation of unmeasured anions.
Anion Gap Calculator with Albumin Correction
What Is the Anion Gap and Why Does It Matter?
The anion gap is the difference between measured cations (sodium) and measured anions (chloride + bicarbonate) in serum. Normally, unmeasured anions like albumin, phosphate, and sulphate account for a gap of 8–12 mEq/L. When additional unmeasured anions accumulate — such as lactate, ketones, or toxins — the gap rises above 12, signalling a high anion gap metabolic acidosis.
Importance of Albumin Correction in Critical Care
Critically ill patients frequently have low albumin levels due to malnutrition, inflammation, or haemodilution. Because albumin itself contributes to the anion gap, hypoalbuminaemia lowers the measured gap and can mask a true elevated-AG acidosis. The albumin-corrected anion gap adds 2.5 mEq/L for each 1 g/dL that albumin falls below 4, revealing the true acid–base status.
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Results are estimates for informational purposes only and do not constitute professional financial, medical, legal, or technical advice. Read full disclaimer →