Anion Gap Calculator (with Albumin Correction)
Enter electrolyte values to calculate the anion gap.
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Anion Gap Calculator (with Albumin Correction) by TheCalcTools
How the Anion Gap Calculator (with Albumin Correction) works
The anion gap estimates unmeasured anions: sodium (plus potassium, if included) minus chloride and bicarbonate. A raised gap points toward causes of metabolic acidosis such as ketoacidosis, lactic acidosis, kidney failure or toxins.
Albumin is the main unmeasured anion, so low albumin lowers the gap; the correction adds 2.5 mEq/L for every 1 g/dL that albumin is below 4. Reference ranges depend on the laboratory’s analyser.
The formula
Worked example
Using the default values shown in the calculator:
| Sodium (mEq/L) | 140 |
|---|---|
| Chloride (mEq/L) | 104 |
| Bicarbonate (mEq/L) | 24 |
| Potassium (mEq/L), optional | 0 |
| Albumin (g/dL), optional | 4 |
- 140 − (104 + 24) = 12 mEq/L.
- With albumin 4.0 the corrected gap is 12.
Result:
| Anion gap (mEq/L) | 12.0 |
|---|---|
| Albumin-corrected anion gap | 12.0 |
| Reading (without potassium, typical lab range about 3 to 11) | Raised |
Frequently asked questions
What is a normal anion gap?
Commonly about 3 to 11 mEq/L without potassium with modern analysers, but older references quote 8 to 16. Use your lab’s range.
Sources and further reading
- Wikipedia: Anion gap
- Kraut JA, Madias NE (2007) Serum anion gap: its uses and limitations. Clin J Am Soc Nephrol 2:162
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This calculator gives general estimates for information and education. It is not medical advice and does not diagnose anything. Talk to a qualified health professional about your own situation. See our disclaimer.