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Anion Gap Calculator
The anion gap is a calculated value from a standard electrolyte panel. It compares the measured positive and negative ions in blood and is most often used when working through a metabolic acidosis — for example with kidney failure, sepsis, diabetic ketoacidosis, or a suspected toxic alcohol ingestion.
Enter the values or tick the options above — the result updates automatically.
How to interpret the result
Reference ranges vary between analysers — many laboratories quote roughly 8–16 mEq/L when potassium is excluded. Two cautions matter more than the exact cut-off:
| Anion gap | What it usually suggests |
|---|---|
| Below ~8 | Uncommon. Low albumin is a frequent cause; also seen with some paraprotein conditions and assay interference. |
| ~8–16 | The usual reference range for most modern analysers (without potassium). |
| Above ~16 | A high anion gap metabolic acidosis pattern — the classic causes are remembered as lactate, ketoacids, kidney failure, and toxins; the clinical picture decides which. |
Albumin lowers the gap: for every 1 g/dL the albumin falls below 4.0 g/dL, the measured gap falls by roughly 2.5 mEq/L, which can hide a raised gap in very unwell patients.
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Frequently asked questions
What is a normal anion gap?
Most laboratories quote roughly 8–16 mEq/L when potassium is not included in the calculation, but the exact range depends on the analyser, so always compare with your own laboratory's reference range.
Why is the anion gap high in diabetic ketoacidosis?
In diabetic ketoacidosis the body produces ketoacids. Their negative ions (ketoanions) are not part of the routine electrolyte panel, so the calculated gap between measured cations and anions widens.
Does albumin affect the anion gap?
Yes. Albumin is a major unmeasured anion, so a low albumin lowers the gap — by about 2.5 mEq/L for every 1 g/dL below 4.0 g/dL. A "normal" gap in a patient with very low albumin can therefore still hide extra acid.
Should potassium be included in the anion gap?
Both versions exist. Most modern practice excludes potassium, giving a reference range of about 8–16 mEq/L. Including potassium gives a higher value and a higher reference range, so it is important to know which version a quoted range belongs to.