Blood Urea Nitrogen (BUN) Test
A blood test that measures the amount of urea nitrogen in your blood to evaluate how well your kidneys and liver are functioning. Urea nitrogen is a waste product that forms when your liver breaks down protein from the food you eat, and healthy kidneys filter it out of your blood and remove it through urine. Your doctor may order this test to check kidney function, monitor kidney disease, evaluate dehydration, or assess how certain medications are affecting your body.
{"The BUN test measures waste product (urea) in your blood from protein breakdown","It helps doctors assess kidney function and detect kidney or liver problems","High BUN levels may indicate kidney disease, dehydration, or heart problems","Low BUN levels may suggest liver disease or malnutrition","The test requires a blood sample, usually taken from a vein in your arm"}
Key facts at a glance
- LOINC
- 12961-9
- Short code
- BUN
- Synonyms
- BUN BldA-mCnc
- Category
- chemistry
- Sample
- whole-blood
- Container
- Lavender top (EDTA) tube or green top (lithium heparin) tube
- Units
- not specified
- Ref low
- 7
- Ref high
- 20
- Critical range
- 5 not specified – 100 not specified
- Fasting
- false
- Population
- adult
- Sex
- all
- Age range
- ≥ 0 years
- Method
- Enzymatic (urease method) or colorimetric (diacetyl monoxime)
- CPT
- 84520
- SNOMED
- 271249004
- Specimen volume
- 2-3 mL whole blood
- Stability
- Room temperature: 24-48 hours; Refrigerated (2-8°C): 7 days; Frozen (-20°C): stable for months. Avoid repeated freeze-thaw cycles.
- Hemolysis max
- 50
- Lipemia max
- 300
- Icterus max
- 20
- TAT
- 1–24 hours
- Order
- routine
What is this test?
The Blood Urea Nitrogen (BUN) test measures the amount of urea nitrogen in your blood. Urea nitrogen is a waste product that forms when your liver breaks down protein from food. Normally, your kidneys filter urea nitrogen from your blood and remove it through urine. This test helps doctors see how well your kidneys are working.
Why do I need this test?
Your doctor may order a BUN test to: check how well your kidneys are working, monitor kidney disease or kidney function, evaluate dehydration, assess liver function, or check the effectiveness of certain medications that may affect kidney function.
How is the test performed?
A healthcare professional will draw a small sample of blood from your artery (or sometimes from a vein in your arm). The blood sample is then sent to a laboratory for analysis. You may need to fast (not eat or drink) for several hours before the test, as instructed by your doctor.
Understanding your results
Normal BUN levels typically range from 7 to 20 mg/dL (milligrams per deciliter). However, normal ranges may vary slightly depending on the laboratory. Higher than normal BUN levels may indicate kidney problems, dehydration, heart failure, or excessive protein intake. Lower than normal BUN levels may suggest liver disease, malnutrition, or overhydration. Your doctor will interpret your results based on your overall health and other test results.
Reference range
7-20 mg/dLnot specified
No special preparation or fasting required
Clinical interpretation
How abnormal results are interpreted and what conditions they suggest.
◆Associated findings1
Frequently asked questions
Does the BUN test hurt?
Are there any risks with this test?
What can affect my BUN results?
Do I need to fast before the test?
Sources
- 1
- 2BUN Test - MedlinePlusSource
- 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 10, 2026. · Read our editorial policy