What Is Anion Gap in a Blood Test? Normal Range Explained
Also known as: AG blood test, serum anion gap
The anion gap is a calculated number, not a directly measured one — it's derived from your sodium, chloride, and bicarbonate (CO2) levels to estimate the balance of acids and bases in your blood. Doctors use it to detect and classify metabolic acidosis. A normal anion gap is roughly 8–12 mmol/L; a high anion gap suggests excess acid in the body.
Anion Gap normal range
| Category | Range (mmol/L) |
|---|---|
| Normal | 8–12 mmol/LRange depends on whether potassium is included |
| High | > 12 mmol/LSuggests metabolic acidosis |
| Low | < 8 mmol/LUncommon; often lab or protein-related |
Reference ranges vary by laboratory. Use the range printed on your own report as the definitive comparison.
What high Anion Gap can mean
- Diabetic ketoacidosis
- Lactic acidosis (from low oxygen delivery, sepsis, etc.)
- Kidney failure
- Certain poisonings or toxins
What low Anion Gap can mean
- Low albumin (the most common cause)
- Laboratory measurement effects
- Rarely, certain blood disorders
What to do about an abnormal result
- A high anion gap is a meaningful signal your doctor investigates promptly, especially with symptoms.
- It's always interpreted with your electrolytes, glucose, and kidney function.
- A mildly abnormal gap without symptoms is often rechecked rather than acted on immediately.
Understand your own results
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Frequently asked questions
What does a high anion gap mean?
A high anion gap usually indicates metabolic acidosis — too much acid in the blood. Common causes include diabetic ketoacidosis, lactic acidosis, kidney failure, and certain toxins. It typically prompts urgent evaluation when paired with symptoms.
Can dehydration cause a high anion gap?
Dehydration can contribute to a high anion gap, often through lactic acidosis or kidney effects. However, the anion gap is interpreted alongside the full metabolic panel to find the underlying cause.
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Medically reviewed by Antonieta Rueda, MD and Ayham Shneker, MD · Last reviewed July 6, 2026
This article is for informational and educational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment. Always seek the advice of your physician or other qualified health provider with any questions you may have regarding a medical condition or your lab results.