Anion Gap (Blood, Calculated from Ions)
This test measures the difference between measured ions in your blood to help assess how well your kidneys are filtering waste products and how your body is balancing acids and bases.
["The anion gap helps diagnose metabolic imbalances, such as kidney disease or acid-base disorders."]
Key facts at a glance
- LOINC
- 73582-9
- Short code
- Anion Gap Bld Calculated.4Ions-sCnc
- Synonyms
- Anion Gap Bld Calculated.4Ions-sCnc
- Category
- chemistry
- Sample
- whole-blood
- Container
- Lavender-top (EDTA)
- Units
- N/A
- Fasting
- false
- Population
- adult
- Sex
- all
- Age range
- 18–65 years
- Method
- calculated-ions
- Specimen volume
- 3 mL
- Stability
- Room temperature: 4h, Refrigerated: 24h
- Hemolysis max
- 0
- Lipemia max
- 0
- Icterus max
- 0
- TAT
- 4–24 hours
- Order
- routine
What Is the Anion Gap Used For?
The anion gap is calculated by subtracting the sum of certain measured ions (like chloride and bicarbonate) from sodium in your blood. It’s not a standalone test but a derived value used alongside other blood chemistry results to identify potential issues like kidney failure, diabetic ketoacidosis, or other metabolic disturbances.
How Is This Test Performed?
A small blood sample is drawn from your arm, typically in the morning for consistency. Your blood is analyzed in a lab to measure sodium, chloride, and bicarbonate levels, which are then used to calculate the anion gap.
Why Might You Need This Test?
Doctors may order this test if you have symptoms like confusion, shortness of breath, nausea, or signs of low blood sugar, kidney problems, or unexplained metabolic acidosis. It helps pinpoint whether a buildup of acids (like ketones) or kidney dysfunction is causing your symptoms.
What Are Common Causes of an Abnormal Anion Gap?
An elevated anion gap often suggests conditions like diabetic ketoacidosis, poisoning (e.g., methanol or ethylene glycol), or severe kidney disease. A normal anion gap may indicate metabolic alkalosis or other less common disorders.
Clinical interpretation
How abnormal results are interpreted and what conditions they suggest.
The anion gap is a critical diagnostic tool in identifying metabolic acidosis caused by non-kidney-related factors. While it doesn’t provide direct answers about kidney function, it helps narrow down whether acid buildup (hyperchloremic acidosis) or other causes (like bicarbonate loss) are at play. High anion gaps may prompt further testing for conditions like diabetic ketoacidosis or toxic exposures, while low or normal gaps may suggest alternative explanations like dehydration or respiratory alkalosis.
Short name
Anion Gap
Frequently asked questions
What does an elevated anion gap mean?
How often should I get this test?
Can diet or medications affect the anion gap?
Sources
- 1
- 2Lab Tests OnlineSource
- 3
Click any link to access the full source. PubMed Central (PMC) links provide free full-text access.
This information is for educational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment.
This content is for general informational and educational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment. Always seek the guidance of a qualified healthcare provider with any questions you have about a medical condition, and never disregard professional medical advice or delay seeking it because of something you read here.
If you think you may have a medical emergency, call your local emergency number or go to the nearest emergency department immediately.
Medically reviewed by WellAlly Editorial Team Last reviewed August 16, 2026. · Read our editorial policy