Anion Gap Calculator helps clinicians and students estimate unmeasured ions from routine electrolytes and spot mixed acid–base problems. It follows standard clinical guidance on anion gap use and albumin correction as summarized by the review by Kraut & Madias (PubMed).

Anion Gap Calculator

mmol/L
mmol/L
mmol/L
Advanced
mEq/L
mmol/L
Anion Gap
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Enter values

Educational use only. Confirm ranges with local lab. Defaults assume 8–16 mEq/L without K or 12–20 mEq/L with K.

Refs: Kraut & Madias • Figge formula

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What this tool does

The tool computes the anion gap (AG) from sodium, chloride, and bicarbonate, with an option to include potassium. It can adjust AG for albumin and compares changes in AG and bicarbonate to screen for mixed disorders (Δ-gap analysis). You get clear ranges, badges, and short cues.

Why anion gap matters

AG is a quick view of “unmeasured” ions in blood. A high AG often signals the build-up of acids. A normal or low AG can point to other issues such as hyperchloremia, hypoalbuminemia, or lab method effects. Used with pH and carbon dioxide, AG helps narrow causes of metabolic acidosis and detect mixed patterns.

Anion Gap Calculator with Albumin Correction and Δ-Gap Analysis

Inputs you can enter

  • Sodium (Na⁺): required.
  • Chloride (Cl⁻): required.
  • Bicarbonate (HCO₃⁻): required.
  • Potassium (K⁺): optional. Toggle on if your lab includes it in AG.
  • Albumin: optional, supports g/dL or g/L for albumin-corrected AG.
  • Normal AG and Normal HCO₃⁻: optional baselines for Δ-gap analysis. Defaults are 12 and 24.

How to use it

  1. Enter Na⁺, Cl⁻, and HCO₃⁻. Toggle potassium if you plan to include K⁺ and enter its value.
  2. Review the Anion Gap result and the badge (normal, high, or low) based on the selected method.
  3. To correct for low albumin, toggle Albumin correction, enter albumin and unit. See the corrected AG beside the raw AG.
  4. Open Advanced to set your site’s or patient’s normal AG and HCO₃⁻ if you use Δ-gap analysis. Read the short cue to screen for mixed disorders.
  5. Use the Reset button to clear everything.

Formulas used

  • AG without K⁺: AG = Na − (Cl + HCO₃)
  • AG with K⁺: AG = (Na + K) − (Cl + HCO₃)
  • Albumin-corrected AG (Figge):
    AGcorr = AG + 2.5 × (4 − albumin[g/dL])
    or equivalently AG + 0.25 × (40 − albumin[g/L])
  • Δ-gap terms: ΔAG = measured AG − normal AG; ΔHCO₃ = normal HCO₃ − measured HCO₃
  • Δ-Δ checks:
    Difference view: ΔAG − ΔHCO₃
    Ratio view: ΔAG / ΔHCO₃

Interpreting the results (simple rules of thumb)

  • High AG: think acid accumulation. Check history and lactate/ketones/tox screens as relevant.
  • Normal AG with low HCO₃⁻: think hyperchloremic (non-gap) acidosis.
  • Albumin effect: low albumin lowers uncorrected AG. Always compare raw vs. corrected.
  • Δ-Δ quick cues:
    • ΔAG − ΔHCO₃ > +6 → suggests a concurrent metabolic alkalosis.
    • ΔAG − ΔHCO₃ < −6 → suggests a concurrent non-gap acidosis.
    • Near zero → changes are roughly matched.

Typical reference ranges

Ranges vary by lab and method. With ion-selective electrodes, normal AG without K⁺ may trend slightly lower than legacy texts. As a practical default:

  • Without K⁺: about 8–16 mEq/L.
  • With K⁺: about 12–20 mEq/L.

Use your local lab’s range when available.

Common causes of high anion gap (GOLD MARK mnemonic)

  • Glycols (ethylene, propylene)
  • Oxoproline (chronic acetaminophen)
  • L-lactate
  • D-lactate
  • Methanol
  • Aspirin (salicylates)
  • Renal failure (uremia)
  • Ketoacidosis (DKA, alcoholic, starvation)

Units and rounding

Inputs and outputs use mmol/L (mEq/L for these ions). The tool rounds to one decimal for readability while keeping internal precision adequate for clinical use.

Worked example

Na⁺ 140, Cl⁻ 104, HCO₃⁻ 18, K⁺ not included, albumin 2.0 g/dL.

  • AG = 140 − (104 + 18) = 18 mEq/L → high AG.
  • AGcorr = 18 + 2.5 × (4 − 2.0) = 23 mEq/L → high even after correction.
  • With normal AG 12 and normal HCO₃⁻ 24: ΔAG = 6; ΔHCO₃ = 6; Δ-Δ diff = 0 → no strong signal of a mixed disorder by this simple screen.

Limitations and good practice

  • AG is a screening aid. Always interpret with pH, PaCO₂, lactate, ketones, toxins, and the clinical picture.
  • Lab methods and reference intervals differ. Confirm your local ranges.
  • Albumin correction helps when albumin is low, but it is still an estimate.

Safety note

This calculator is for education and workflow support. It does not diagnose or replace clinical judgment.