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Anion Gap Calculator
Table of Contents
**Updates**
We updated this page on 23rd of November 2025, added interactive Anion Gap Calculator and explainer on what is the anion gap. Added a detailed explanation of how the calculator works, and added related questions to the FAQs section.
What is the anion gap?
It helps to find hidden acids in your blood.
High gap = unmeasured acids which points to toxins, diabetes, or kidney issues.
Normal gap ≠ all clear, you can still have other acid problems.
Anion gap is a metabolic detective:
- Think of your blood like a balanced see-saw. The anion gap measures the acids we can't directly test for. The maths is: Sodium - (Chloride + Bicarbonate).
High gap = unmeasured acids:
- When gap jumps above 16, your body's dealing with "uninvited guests" – lactic acid (from severe infection), ketones (diabetic crisis), or toxins.
Normal gap ≠ all clear:
- Your gap can be normal (8-12) while still having acidosis. This happens with diarrhea or kidney damage – you lose bicarbonate but chloride rises, keeping the math "balanced" while your blood gets acidic.
Albumin changes the rules:
- Albumin acts like a sponge for acid. Low albumin? Fewer sponges. Your gap looks normal but hidden acids are brewing.
Anion Gap - The difference between measured electrolytes.
Metabolic Acidosis - Blood too acidic from disease (not lungs).
Albumin - Blood protein that soaks up acid – your body's acid sponge.
How to use the anion gap calculator
- Enter your lab values - Sodium, Chloride, and Bicarbonate.
- Add albumin if known to get the corrected, more accurate gap.
- Click "Calculate" to see results.
- If you need to redo, click "Reset" to start fresh.
**All information is private, no data is saved or shared.**
Anion Gap Calculator
Disclaimer
The online clinical calculators provided on Aidstat.com are intended for informational purposes only. They are not a substitute for clinical reasoning, professional judgement, or expert advice from qualified healthcare practitioners.
While extensive effort has been made to ensure the accuracy and completeness of the information provided by these calculators, Aidstat.com cannot guarantee its accuracy or reliability. Users are advised to independently verify any results obtained through the use of these tools before making any medical or healthcare decisions.
Anion Gap Calculator
Quickly calculate anion gap. Optional albumin correction included.
FAQs
Q1. What does this "Gap" actually measure in my blood?
- Your blood contains positive charges (sodium, potassium) and negative charges (chloride, bicarbonate).
- The "gap" is the unmeasured negative ions - mostly acids from metabolism or toxins.
Q2. Why don't you include potassium in the calculation?
- Potassium levels change too rapidly, it jumps between cells and blood constantly.
- While technically a positive ion, its concentration is so low (3.5-5 mEq/L vs sodium's 135-145) that including it adds noise without better accuracy.
- *Emergency medicine protocols* specifically use the sodium-only formula for faster, more reliable decisions.
Q3. What causes a high anion gap?
- Diabetic emergencies - Ketones flood the blood.
- Lactic acidosis - Oxygen starvation from shock or sepsis.
- Kidney failure - Can't remove normal acids.
- Toxins - Alcohol, antifreeze, aspirin overdoses.
- A high gap above 16 needs same day medical attention - it rarely goes away on its own.
Q4. How Can You Have Acid Problems With a "Normal" Gap?
- Diarrhea - Loses bicarbonate, gains chloride.
- Kidney tube defects - Can't hold onto bicarbonate.
- Certain medications - Especially for blood pressure.
- IV fluids - Massive saline can dilute bicarbonate.
References
1. Achanti, A. and Szerlip, H.M. (2022). Acid-Base Disorders in the Critically Ill Patient. Clinical Journal of the American Society of Nephrology, 18(1), p.CJN.04500422. doi:https://doi.org/10.2215/cjn.04500422. Link
2. Diagnostic Use of Base Excess in Acid–Base Disorders. (2018). New England Journal of Medicine, 379(5), pp.494–496. doi:https://doi.org/10.1056/nejmc1806372. Link
3. Kraut, J.A. and Madias, N.E. (2007). Serum anion gap: its uses and limitations in clinical medicine. Clinical journal of the American Society of Nephrology: CJASN, [online] 2(1), pp.162–174. doi:https://doi.org/10.2215/CJN.03020906. Link
4. Morgan, T.J. (2009). The Stewart Approach – One Clinician’s Perspective. The Clinical Biochemist Reviews, [online] 30(2), p.41. Available at: https://pmc.ncbi.nlm.nih.gov/articles/PMC2702213 [Accessed 23 Nov. 2025]. Link