Anion Gap Calculator
Simple anion-gap arithmetic from electrolytes — not a differential diagnosis. Click any i for detail.
Electrolytes
Sodium Na (mEq/L)
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Na
Serum sodium. |
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|---|---|
Chloride Cl (mEq/L)
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Cl
Serum chloride. |
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Bicarbonate HCO₃ (mEq/L)
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HCO3
Total CO₂ / bicarbonate on the metabolic panel. |
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Include potassium?
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K mode
Some labs historically added K; many modern gaps omit it. |
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Potassium K (mEq/L)
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K
Only used when include-K is yes. |
How to use this calculator
- Enter Na, Cl, and HCO₃.
- Choose whether to include K.
- Read the gap in mEq/L.
- Interpret only with a clinician and the lab’s reference range.
Results explained
The anion gap estimates unmeasured anions in serum. The common clinical form is Na − (Cl + HCO₃). Including potassium raises the number and changes reference ranges. Albumin, lithium, and lab methods shift interpretation — this page only does the arithmetic.
Quick reference: anion gap
Gap = Na − (Cl + HCO₃), optional +K.
| Item | Detail |
|---|---|
| Without K | Common modern teaching form |
| With K | Older textbooks / some labs |
| High gap | Many causes — needs clinical context |
| Low gap | Also needs context (e.g., albumin) |
Educational worksheet only — not a diagnosis.
How the estimate is built
AG = Na − (Cl + HCO₃) or AG = Na + K − (Cl + HCO₃).
Example scenario
Na 140, Cl 104, HCO₃ 24 → gap 12 mEq/L (without K).
FAQ
What is a normal gap?
Depends on the lab and whether K is included. Use the reference range printed on the report.
Do I correct for albumin?
Clinicians sometimes adjust for hypoalbuminemia. This page does not.
SI units?
Enter values consistently in mEq/L (or mmol/L for these electrolytes).
Is this ABG or VBG?
It uses the electrolyte panel bicarbonate / total CO₂ you enter — not a full blood-gas interpretation.