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 working. Urea nitrogen is a waste product formed when your body breaks down protein, and healthy kidneys filter it out of your blood. This test helps your doctor check kidney function, find possible kidney problems, or monitor how well treatments such as dialysis are working.
{"The BUN test measures waste product (urea) in your blood","Elevated BUN may indicate kidney problems or dehydration","The test requires a simple blood draw","Results help doctors assess kidney and liver function"}
Key facts at a glance
- LOINC
- 59570-2
- Short code
- BUN
- Synonyms
- BUN Bld-sCnc
- Category
- chemistry
- Sample
- whole-blood
- Container
- Serum separator tube (SST) or plain red top tube; EDTA or heparin plasma acceptable for plasma
- Units
- not specified
- Ref low
- 2.1
- Ref high
- 8.5
- Critical range
- 1 not specified – 35.7 not specified
- Fasting
- false
- Population
- adult
- Sex
- all
- Age range
- 0–120 years
- Method
- Enzymatic (Urease) or Colorimetric
- CPT
- 84520
- SNOMED
- 271295004
- Specimen volume
- 2-5 mL whole blood
- Stability
- Room temperature: 7 days; Refrigerated (2-8°C): 7 days; Frozen (-20°C): 30 days. Avoid repeated freeze-thaw cycles.
- Hemolysis max
- 50
- Lipemia max
- 300
- Icterus max
- 40
- 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 is a waste product formed when your liver breaks down protein from the foods you eat. Normally, your kidneys filter urea from your blood and remove it through urine.
Why is this test performed?
Your doctor may order a BUN test to check how well your kidneys are working. It is often part of a routine blood panel (comprehensive metabolic panel or basic metabolic panel). The test can help diagnose kidney disease, monitor kidney function, or evaluate the effectiveness of dialysis treatment.
How is the test done?
A healthcare professional will draw a small sample of blood from a vein in your arm using a needle. The blood sample is then sent to a laboratory for analysis. You do not need to fast before this test, but your doctor may ask you to avoid certain medications or supplements beforehand.
Understanding your results
Normal BUN levels typically range from 7 to 20 mg/dL (2.5 to 7.1 mmol/L). However, normal ranges may vary slightly depending on the laboratory and your individual health factors. Your doctor will interpret your results based on your overall health and other test results.
Reference range
2.1-8.5 mmol/Lnot specified
No special preparation or fasting required; high-protein diet may elevate results
Clinical interpretation
How abnormal results are interpreted and what conditions they suggest.
High BUN levels (azotemia) may indicate: kidney dysfunction or kidney disease, dehydration, heart failure, excessive protein intake, or bleeding in the digestive tract. Low BUN levels may be caused by liver disease, overhydration, or malnutrition. Your doctor will consider your BUN results alongside other tests (like creatinine) to get a complete picture of your kidney function.
Frequently asked questions
Do I need to fast before a BUN test?
What does a high BUN level mean?
Can medications affect BUN results?
Is the BUN test dangerous?
Sources
- 1
- 2
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