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Anion Gap Calculator

📅Last updated: October 5, 2025
✓Reviewed by: LumoCalculator Team

Enter Na⁺, Cl⁻, HCO₃⁻ with optional K⁺ and albumin to compute AG and albumin-corrected AG. Includes normal range and quick interpretation for acid–base assessment.

Anion Gap Inputs

Electrolytes (mmol/L)
Albumin & Options

Your Results

12
mmol/L (Anion Gap)

Albumin ≥ 4 g/dL; correction not needed.

Interpretation: Normal anion gap (thresholds exclude K⁺)

Normal range used: ≈8–12 mmol/L (excludes K⁺); verify with local lab ranges.

Common Causes of High Anion Gap

Metabolic
  • • Lactic acidosis
  • • Ketoacidosis (DKA, starvation, alcohol)
  • • Renal failure (uremia)
Toxins
  • • Methanol / Ethylene glycol
  • • Salicylates
  • • Paraldehyde (rare)

How to Calculate Anion Gap

Formulas

Standard: AG = Na⁺ − (Cl⁻ + HCO₃⁻)1
With K⁺: AG = (Na⁺ + K⁺) − (Cl⁻ + HCO₃⁻)1
Corrected: AGcorr = AG + 2.5 × (4 − albumin[g/dL])2

Reference Ranges & Notes

  • Typical AG (without K⁺): 8–12 mmol/L; with K⁺ included: ≈12–16 mmol/L.
  • Correct when albumin is low: AGcorr = AG + 2.5 × (4 − albumin[g/dL]).
  • High AG suggests unmeasured anions (e.g., lactate, ketones, toxins).
  • Interpret results in clinical context and alongside blood gas when needed.

Calculation Steps:

  1. 1
    Enter electrolytes
    Na⁺, Cl⁻, HCO₃⁻; optionally K⁺ and albumin
  2. 2
    Choose whether to include K⁺
    Most labs report AG without K⁺
  3. 3
    Apply albumin correction if provided
    Use corrected AG when albumin is low

References

  1. StatPearls: High Anion Gap Metabolic Acidosis (NIH/NCBI)
  2. Figge J et al. Serum proteins and acid-base equilibria. J Lab Clin Med. 1998.

Important Considerations

⚠️ Medical Disclaimer

This calculator provides estimates. Consult healthcare professionals for medical advice.

🧪 Lab Context

Ranges depend on analyzer and method

  • • Check local reference
  • • Confirm units as mmol/L
  • • Recheck unexpected results
🩺 Clinical Correlation

Interpret with history and ABG

  • • Consider lactate/ketones
  • • Review renal function
  • • Screen for toxins as indicated
📉 Low Albumin

May mask elevated AG

  • • Use corrected AG
  • • Look for liver disease, malnutrition
  • • Track albumin trend
⚠️ Interferences

Rare ionic interferences can lower AG

  • • Paraproteins
  • • Bromide/iodide
  • • Lithium

Example Cases

Case 1: Standard AG

Inputs: Na⁺ 140, Cl⁻ 104, HCO₃⁻ 24
AG: 12 mmol/L (normal)

Case 2: Corrected AG

Inputs: Na⁺ 140, Cl⁻ 100, HCO₃⁻ 16, albumin 2.0
AG: 24 mmol/L; AGcorr: 29 mmol/L

Frequently Asked Questions

What is the anion gap (AG)?
Anion gap estimates unmeasured anions in plasma. The usual formula is AG = Na⁺ − (Cl⁻ + HCO₃⁻). Some labs include K⁺: (Na⁺+K⁺) − (Cl⁻+HCO₃⁻).
What is the normal range of anion gap?
Typically 8–12 mmol/L (mEq/L) without K⁺, depending on the laboratory method. Always interpret with local reference ranges.
When is corrected AG needed?
Albumin is a major unmeasured anion. Use corrected AG = AG + 2.5 × (4 − albumin[g/dL]) when albumin is low to avoid underestimating the gap.
How is AG used clinically?
Primarily to evaluate metabolic acidosis and to detect high anion gap causes such as lactic acidosis, ketoacidosis, renal failure, or certain toxins.
Does a low AG matter?
Low AG can be due to hypoalbuminemia, lab variation, paraproteinemia, or rare ionic interferences. It should be correlated clinically.

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