What this calculator does
Anion gap works out unmeasured ions in the blood, a first step in narrowing the cause of a metabolic acidosis. Enter your own figures above and the answer updates as you type: nothing is fixed in the code, so the result reflects exactly the numbers you supply.
The formula this calculator evaluates is printed under the tool and explained below, so you can check the working by hand or reuse it in a spreadsheet.
The formula
FormulaAnion gap = Na − (Cl + HCO3)
The inputs explained
| Field | What to enter |
|---|---|
| Sodium (mEq/L) | A number, measured in mEq/L. Starts at 140. |
| Chloride (mEq/L) | A number, measured in mEq/L. Starts at 104. |
| Bicarbonate (HCO3) (mEq/L) | A number, measured in mEq/L. Starts at 24. |
Worked examples
Every figure in the tables below is produced by this page’s own calculator at build time, so the numbers and the tool always agree. Select any row to load that scenario.
How the answer changes with sodium
Every other input is held at the calculator’s starting values while sodium varies. Select any row to load that scenario into the calculator.
How the answer changes with sodium
| Sodium (mEq/L) | Anion gap | Reference range | Reading |
|---|---|---|---|
| 70 | -58.0 mEq/L | 8 - 12 mEq/L | Below the reference range |
| 105 | -23.0 mEq/L | 8 - 12 mEq/L | Below the reference range |
| 140 | 12.0 mEq/L | 8 - 12 mEq/L | Within the reference range |
| 210 | 82.0 mEq/L | 8 - 12 mEq/L | Above the reference range: worth discussing with a clinician |
| 280 | 152.0 mEq/L | 8 - 12 mEq/L | Above the reference range: worth discussing with a clinician |
| 420 | 292.0 mEq/L | 8 - 12 mEq/L | Above the reference range: worth discussing with a clinician |