Anion Gap (Serum/Plasma) Calculated from Ions
This test measures the difference between key 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 conditions like kidney disease or metabolic acidosis."]
Key facts at a glance
- LOINC
- 77341-6
- Short code
- AGAP
- Synonyms
- Anion Gap SerPlBld Calculated.4Ions-sCnc
- Category
- chemistry
- Sample
- serum
- Container
- Serum separator tube (SST) or plasma separator tube (PST); lithium heparin or sodium heparin acceptable for plasma
- Units
- N/A
- Ref low
- 8
- Ref high
- 16
- Critical range
- 4 N/A – 20 N/A
- Fasting
- false
- Population
- adult
- Sex
- all
- Age range
- 18–65 years
- Method
- calculated-ions
- CPT
- 80051
- SNOMED
- 271075000
- Specimen volume
- 1 mL of serum or plasma
- Stability
- Room temperature: 8 hours; Refrigerated (2-8°C): 7 days; Frozen (-20°C): 30 days
- Hemolysis max
- 100
- Lipemia max
- 200
- Icterus max
- 40
- TAT
- 1–4 hours
- Order
- routine
Why Is This Test Done?
Your doctor may order this test if you have symptoms like confusion, shortness of breath, or unusual fatigue, or if they suspect an imbalance in your body’s chemistry—such as from kidney problems, diabetes, or certain medications.
What Does It Measure?
The test calculates the gap between positively charged ions (like sodium) and negatively charged ions (like chloride and bicarbonate) in your blood. This gap can reveal whether your body is producing too much acid or if your kidneys are not working properly.
How Is It Done?
A small blood sample is taken from a vein, usually in your arm. The sample is sent to a lab where it is analyzed to determine the measured ion concentrations and the resulting anion gap.
What Are Common Causes?
High anion gaps may occur due to conditions like diabetic ketoacidosis, poisoning, or severe kidney disease. Low anion gaps are less common but can happen with overhydration or certain blood disorders.
Reference range
8-16 mmol/L (calculated as Na+ + K+ - Cl- - HCO3-)N/A
No special preparation required. Fasting is not necessary.
Clinical interpretation
How abnormal results are interpreted and what conditions they suggest.
A high anion gap often signals metabolic acidosis, where the body’s acid levels rise. This can be caused by conditions that increase acid production (e.g., ketoacidosis) or impair kidney function. A low anion gap may indicate overhydration or conditions affecting sodium levels.
Short name
Anion Gap
Frequently asked questions
What if My Results Are Abnormal?
Will I Need to Prepare for This Test?
How Long Does It Take to Get Results?
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