Higher anion gap
A higher value can reflect an increase in unmeasured anions, including lactate or ketoacids. The number alone does not establish the cause.
Anion Gap Calculator
Enter serum measurements
Clinical overview
What Is the Anion Gap
This calculated value estimates the electrical charge carried by ions that are not listed individually on a routine serum electrolyte panel.
Blood remains electrically neutral, so positive ions and negative ions balance overall. A basic metabolic panel measures only part of that balance. Subtracting chloride and bicarbonate from sodium reveals the difference between the routinely measured cations and anions.
Clinicians use this value as one part of an acid-base assessment, particularly when metabolic acidosis is being evaluated. The result is not a direct measurement and cannot identify a cause by itself.
Formula and example
How to Calculate the Anion Gap
Use sodium, chloride, and bicarbonate results from the same blood sample. Enter potassium only when your laboratory or clinical protocol uses the potassium-inclusive version of the formula.
Common formula without potassium
AG = Na⁺ − (Cl⁻ + HCO₃⁻)
Formula with potassium
AG = Na⁺ + K⁺ − (Cl⁻ + HCO₃⁻)
The calculator starts K⁺ at zero, so it follows the common formula unless you enter a potassium value. For these monovalent electrolytes, results reported in mmol/L have the same numerical value as mEq/L.
- Copy the Na⁺, Cl⁻, and HCO₃⁻ values from one laboratory report.
- Leave K⁺ at zero or enter the measured potassium concentration.
- Review the live equation and the calculated result in mEq/L.
Worked calculation
- Na⁺
- 140 mEq/L
- Cl⁻
- 105 mEq/L
- HCO₃⁻
- 24 mEq/L
- K⁺
- 0 mEq/L
140 − (105 + 24) = 11 mEq/L
The result is 11 mEq/L. If K⁺ were entered as 4 mEq/L, the potassium-inclusive result would be 15 mEq/L.
Corrected result
Why Correct the Anion Gap for Albumin
Albumin is a major unmeasured anion, so a low serum albumin concentration can make the observed gap appear lower than it otherwise would.
When albumin is available, this calculator estimates a corrected result using a reference albumin concentration of 4.4 g/dL. The correction is displayed separately, leaving the uncorrected result visible for comparison.
Albumin correction formula
Corrected AG = AG + 2.5 × (4.4 − albumin)
Albumin correction example
Using the previous result of 11 mEq/L and an albumin value of 3.0 g/dL:
11 + 2.5 × (4.4 − 3.0) = 14.5 mEq/L
The albumin-corrected value is 14.5 mEq/L.
The albumin adjustment follows the Figge correction described in research indexed by the National Library of Medicine.
Reading the value
How to Interpret Anion Gap Results
There is no single universal reference range for this calculation. The expected interval depends on the analyzer, laboratory method, albumin concentration, and whether potassium is included in the equation.
Check the laboratory range first. The source examples use approximately 3–11 mEq/L without potassium and 5–16 mEq/L with potassium. Other clinical references commonly cite about 4–12 mEq/L for the formula without K⁺.
Reference-range anion gap
A result within range does not rule out an acid-base disorder. Bicarbonate loss accompanied by a chloride rise may produce a normal-gap, hyperchloremic pattern.
Lower anion gap
A lower value is often associated with reduced albumin, although measurement factors and other clinical conditions also need consideration.
Reference intervals and clinical context are discussed in this NCBI clinical overview. Use the range printed by the reporting laboratory whenever it is available.
Common questions
Anion Gap Calculator FAQ
Which values does the anion gap calculator use?
Sodium, chloride, and bicarbonate are required. Potassium is optional and starts at zero, while albumin is only needed for the corrected result.
Should potassium be included in the anion gap formula?
Many laboratories omit potassium because its concentration is small compared with sodium. Keep K⁺ at zero for that convention or enter the measured value when the potassium-inclusive formula is required.
Why is the anion gap corrected for albumin?
Albumin is a major unmeasured anion. A low albumin concentration can lower the observed gap, so the correction estimates what the result would be at an albumin concentration of 4.4 g/dL.
Does a high anion gap provide a diagnosis?
No. The anion gap is one calculated part of an acid-base assessment and must be interpreted with symptoms, blood pH, other laboratory results, and the reporting laboratory's reference interval.
Can electrolyte values in mmol/L be used?
For the monovalent electrolytes used here, Na⁺, K⁺, Cl⁻, and HCO₃⁻ have the same numerical value in mmol/L and mEq/L. Albumin must be entered in g/dL.