Anion Gap (Calculated from Serum/Plasma Ion Concentrations)
This test measures the difference between measured ions in your blood to help assess metabolic health, particularly acid-base balance and potential conditions like diabetic ketoacidosis or kidney disease.
["The anion gap helps identify imbalances that may require medical attention."]
Key facts at a glance
- LOINC
- 1863-0
- Short code
- AGAP
- Synonyms
- Anion Gap SerPl Calculated.4Ions-sCnc
- Category
- chemistry
- Sample
- serum
- Container
- Serum separator tube (SST) or plasma separator tube (PST) with lithium heparin
- Units
- N/A
- Ref low
- 8
- Ref high
- 16
- Fasting
- false
- Population
- adult
- Sex
- all
- Age range
- 18–65 years
- Method
- calculated-ions
- SNOMED
- 169252003
- Specimen volume
- 1 mL of serum or plasma
- Stability
- Stable for 8 hours at room temperature, 48 hours refrigerated at 2-8°C, and 2 weeks frozen at -20°C
- Hemolysis max
- 500
- Lipemia max
- 1000
- Icterus max
- 500
- TAT
- 1–4 hours
- Order
- routine
What Is the Anion Gap Used For?
Doctors use the anion gap to diagnose and monitor conditions affecting how your body handles acids and bases. It can help spot problems like severe dehydration, kidney failure, or metabolic acidosis that may not show up in other tests alone.
How Is the Anion Gap Calculated?
The anion gap is calculated by subtracting the total measured anions (like chloride and bicarbonate) from the sodium ion concentration in your blood. This value reflects the presence of unmeasured anions that may be contributing to acidity.
Why Might You Need This Test?
You may need this test if you have symptoms like confusion, rapid breathing, nausea, or unexplained fatigue, or if your doctor suspects conditions like diabetic ketoacidosis, poisoning, or kidney disease.
What Does a High or Low Anion Gap Mean?
A high anion gap often signals metabolic acidosis caused by conditions like diabetic ketoacidosis or lactic acidosis. A low anion gap may indicate chronic kidney disease or other conditions affecting ion balance.
Reference range
Adult: 8-16 mmol/L; Pediatric: varies by ageN/A
No special patient preparation required. Fasting is not necessary.
Clinical interpretation
How abnormal results are interpreted and what conditions they suggest.
Clinical Significance: The anion gap is a critical tool for diagnosing and managing metabolic disturbances. It helps differentiate between types of acidosis (e.g., diabetic ketoacidosis vs. kidney failure) and guides treatment decisions. Always discuss results with your healthcare provider, as interpretation depends on your overall health and symptoms.
Short name
Anion Gap
Frequently asked questions
Why do doctors calculate the anion gap from serum/plasma rather than whole blood?
How often should I get this test?
Can lifestyle changes 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