Blood Urea Nitrogen (BUN) Test
The blood urea nitrogen (BUN) test is a simple blood test that measures the level of urea nitrogen, a waste product your body produces when it breaks down protein from the food you eat. Since healthy kidneys filter this waste from your blood and remove it through urine, this test helps your doctor evaluate how well your kidneys are working and can help detect kidney problems early.
{"BUN test measures waste product levels in your blood (normal range: 7-20 mg/dL)","Higher than normal BUN levels may indicate kidney problems or dehydration","Lower than normal BUN levels may suggest liver disease or malnutrition","The test is often done along with other kidney function tests like creatinine","No special preparation is usually needed, but follow your doctor's instructions"}
Key facts at a glance
- LOINC
- 6299-2
- Short code
- BUN
- Synonyms
- BUN Bld-mCnc
- Category
- chemistry
- Sample
- whole-blood
- Container
- Serum separator tube (SST) or plasma separator tube (PST). Also acceptable: lavender top (EDTA), gray top (sodium fluoride/potassium oxalate), or green top (heparin) plasma tubes.
- 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 with spectrophotometric detection
- CPT
- 84520
- SNOMED
- 271344006
- Specimen volume
- 1.0-2.5 mL of whole blood
- Stability
- Room temperature: 24-72 hours. Refrigerated (2-8°C): 7 days. Frozen (-20°C): 30 days. Avoid repeated freeze-thaw cycles.
- Hemolysis max
- 50
- Lipemia max
- 300
- Icterus max
- 20
- TAT
- 1–24 hours
- Order
- routine
What is the Blood Urea Nitrogen (BUN) Test?
The Blood Urea Nitrogen (BUN) test is a common blood test that measures the amount of urea nitrogen in your blood. Urea nitrogen is a waste product that forms when your body breaks down protein from the foods you eat. Normally, your kidneys filter urea nitrogen out of your blood and excrete it in urine. This test helps doctors evaluate how well your kidneys are working to remove this waste product from your body.
How is the test performed?
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. The procedure is quick and typically takes only a few minutes. You may feel a slight sting when the needle is inserted or removed.
What do the results mean?
Normal BUN levels typically range from 7 to 20 mg/dL (2.5 to 7.1 mmol/L). However, normal ranges may vary slightly among different laboratories. Your doctor will interpret your results based on your overall health, age, and other factors.
Reference range
7-20 mg/dLnot specified
No fasting or special preparation required
Clinical interpretation
How abnormal results are interpreted and what conditions they suggest.
Elevated BUN levels (azotemia) may indicate: kidney disease or kidney failure, dehydration or inadequate fluid intake, heart failure, excessive protein breakdown, certain medications, or urinary tract obstruction. Lower than normal BUN levels may suggest: liver disease, malnutrition, overhydration, or pregnancy. The BUN test is often paired with the creatinine test to provide a more complete picture of kidney function. The BUN-to-creatinine ratio can help doctors determine the cause of abnormal kidney function results.
Frequently asked questions
Do I need to fast before the BUN test?
Is the BUN test painful?
How often should I have a BUN test?
What can I do to keep my BUN levels normal?
Sources
- 1
- 2
- 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