Anion Gap (Calculated) from Blood
This test measures the difference between measured ions in your blood to help assess how well your kidneys are filtering waste products and whether your body is producing too much acid.
["The anion gap helps identify metabolic imbalances, often linked to kidney or liver issues or conditions like diabetic ketoacidosis."]
Key facts at a glance
- LOINC
- 95718-3
- Short code
- AG3I
- Synonyms
- Anion Gap Bld Calculated.3Ions-sCnc
- Category
- chemistry
- Sample
- whole-blood
- Container
- Lithium heparin plasma separator tube (PST) preferred; alternatively, serum separator tube (SST). Whole blood collected in lithium heparin tube for STAT analysis.
- Units
- N/A
- Ref low
- 8
- Ref high
- 16
- Critical range
- 4 N/A – 30 N/A
- Fasting
- false
- Population
- adult
- Sex
- all
- Age range
- 0–120 years
- Method
- calculated-ions
- CPT
- 80051 (Electrolyte panel includes calculated anion gap)
- SNOMED
- 121006009
- Specimen volume
- 1-3 mL of whole blood (minimum 0.5 mL plasma or serum required for analysis).
- Stability
- Plasma/serum stable for 24 hours at room temperature (15-25°C), up to 48 hours refrigerated at 2-8°C, and up to 2 weeks frozen at -20°C. Avoid prolonged exposure to ambient air, which alters bicarbonate concentration.
- Hemolysis max
- 50
- Lipemia max
- 100
- Icterus max
- 25
- TAT
- 1–4 hours
- Order
- routine
Why This Test Matters
Your blood contains several charged particles (ions) that help maintain balance. The anion gap compares the total amount of negatively charged ions (like chloride and bicarbonate) to the positively charged ions (like sodium). A gap that’s too high or too low can signal problems with how your body processes waste or acid, which may require medical attention.
How It’s Done
A small blood sample is drawn from your arm. The lab calculates the gap using standard formulas based on sodium, chloride, and bicarbonate levels measured in your blood.
Common Causes of Abnormal Results
High anion gaps may occur with conditions like kidney failure, diabetic ketoacidosis, or poisoning from certain toxins. Low gaps are less common but can happen with severe dehydration or overuse of certain medications.
What to Expect Before or After
No special preparation is needed, but you may feel slight discomfort from the needle. Results are typically ready within 24 hours and shared with your healthcare provider.
Reference range
Adult: 8-16 mEq/L (mmol/L); some laboratories report 7-15 mEq/L or 10-20 mEq/L depending on institutional reference. Pediatric ranges are generally similar to adults. Newborns may have slightly lower reference values.N/A
No special patient preparation required. Fasting is not necessary. Avoid tourniquet application for prolonged periods, which may alter electrolyte concentrations due to hemoconcentration.
Clinical interpretation
How abnormal results are interpreted and what conditions they suggest.
Clinical Significance: Anion Gap as a Diagnostic Tool
Short name
Anion Gap
Frequently asked questions
What does an elevated anion gap mean in my results?
Could a low anion gap indicate a problem?
Does this test replace other blood tests?
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 15, 2026. · Read our editorial policy