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The Blood Urea Nitrogen (BUN) test measures the amount of urea nitrogen in your blood, helping doctors evaluate how well your kidneys are functioning.
{"Measures urea nitrogen, a waste product filtered out by kidneys","Helps assess kidney function and hydration status","Results are interpreted along with other tests like creatinine"}
Key facts at a glance
- LOINC
- 3093-2
- Short code
- BUN
- Synonyms
- Urea nit Fld-mCnc
- Category
- chemistry
- Sample
- serum
- Container
- Serum separator tube (SST) or plain red top 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) method
- CPT
- 84520
- SNOMED
- 271224006
- Specimen volume
- 1-2 mL serum minimum
- Stability
- Room temperature: 24 hours; Refrigerated (2-8°C): 72 hours; Frozen (-20°C): 1 week
- 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 is a waste product formed when your liver breaks down protein from food. Normally, your kidneys filter urea out of your blood and it leaves your body in urine. The BUN test shows how well your kidneys are removing this waste.
Why do I need this test?
Your doctor may order a BUN test to check how well your kidneys are working. It is often part of a routine blood test called a metabolic panel. The test can also help evaluate your hydration status and monitor kidney disease or damage.
How is the test done?
A healthcare provider will take a small blood sample from a vein in your arm using a needle. The sample is then sent to a laboratory for analysis. You may need to fast (not eat) for several hours before the test, depending on your doctor's instructions.
What do the results mean?
BUN results are reported as milligrams of urea nitrogen per deciliter of blood (mg/dL). Normal ranges vary by laboratory but are typically between 7 and 20 mg/dL. Higher than normal BUN levels may indicate kidney problems, dehydration, or a high-protein diet. Lower than normal levels may be due to liver disease, overhydration, or a low-protein diet. Your doctor will interpret your results based on your overall health and other test results.
Reference range
No established reference range (interpret relative to concurrent serum)not specified
No special preparation; body fluid collected by clinician
Clinical interpretation
How abnormal results are interpreted and what conditions they suggest.
◆Associated findings1
Frequently asked questions
Do I need to fast before a BUN test?
What can affect my BUN results?
Is the BUN test dangerous?
How often should I have a BUN test?
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