Anion Gap Calculator
Calculate your serum anion gap from sodium, chloride and bicarbonate.
What is the anion gap?
The anion gap is a number worked out from your routine electrolytes. Blood has to stay electrically balanced, so the positively charged ions (mainly sodium) and the negatively charged ions (mainly chloride and bicarbonate) should roughly match. The "gap" between them stands in for the acids and other particles that are not routinely measured. It is used mostly to screen for, and sort out the cause of, metabolic acidosis (too much acid in the blood).
How this calculator works
It uses the common formula without potassium: anion gap = sodium - (chloride + bicarbonate), with all values in mEq/L. These numbers are the same in mmol/L, so no unit toggle is needed. Everything is calculated in your browser and nothing is stored.
What your result means
| Anion gap | Interpretation |
|---|---|
| Below 8 mEq/L | Low |
| 8 to 12 mEq/L | Normal |
| Above 12 mEq/L | High (possible metabolic acidosis) |
The normal range genuinely varies between laboratories and analysers - some report up to about 16 as normal - so always compare against your own report's reference range. A version of the formula that adds potassium will read about 4 higher.
What abnormal values can mean
A high anion gap can accompany diabetic ketoacidosis, lactic acidosis (for example in severe infection), advanced kidney failure, or certain poisonings. A low anion gap is less common and is most often caused by a low blood albumin. The anion gap is only one clue, and it is interpreted alongside your pH, bicarbonate and clinical picture. Discuss any abnormal result with your doctor.
Frequently asked questions
What is the anion gap?
It is a number calculated from your electrolytes that helps doctors screen for acid-base disorders, especially metabolic acidosis. It reflects unmeasured acids in the blood.
What is a normal anion gap?
Commonly about 8 to 12 mEq/L when potassium is not included, but the normal range depends on the lab and the analyser used, so check your report.
Why do some formulas include potassium?
One version uses (Na + K) - (Cl + HCO3), which raises the normal range by roughly 4. This calculator uses the more common version without potassium.
What does a high anion gap mean?
It can point to causes of metabolic acidosis such as diabetic ketoacidosis, lactic acidosis, kidney failure or certain poisonings. The number is only a clue - your doctor interprets it with the full clinical picture.
Can the anion gap be low?
Yes, though it is less common. A low albumin is the usual reason, and occasionally it reflects a lab measurement issue.
Formula source: Kraut JA, Madias NE. Serum anion gap: its uses and limitations in clinical medicine. Clin J Am Soc Nephrol 2007;2:162-174.
Related reading
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