Blood Urea Nitrogen (BUN) Test
A blood test that measures the amount of urea nitrogen in your blood to evaluate how well your kidneys are functioning. This simple screening helps your doctor detect kidney problems, dehydration, and other conditions that may affect your kidney health early on.
{"BUN test measures waste product (urea) in your blood","Helps assess kidney function and hydration status","Results are reported in mg/dL; normal range is typically 7-20 mg/dL","Higher levels may indicate kidney problems or dehydration","Often paired with creatinine test for complete kidney assessment"}
Key facts at a glance
- LOINC
- 3094-0
- Short code
- BUN
- Synonyms
- —
- Category
- kidney
- Sample
- serum
- Container
- Serum Separator Tube (SST/Gold Top) or Red Top Tube
- Units
- mg/dL
- Ref low
- 7
- Ref high
- 20
- Critical range
- 5 mg/dL – 100 mg/dL
- Fasting
- false
- Population
- adult
- Sex
- all
- Age range
- 0–150 years
- Method
- urease
- CPT
- 84520
- SNOMED
- 271224006
- Specimen volume
- 3-5 mL
- Stability
- Room temperature: 24-48 hours, Refrigerated (2-8°C): 7 days, Frozen (-20°C or below): 30 days
- Hemolysis max
- 50
- Lipemia max
- 300
- Icterus max
- 20
- TAT
- 1–4 hours
What is a 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 liver breaks down protein from the foods you eat. Normally, your kidneys filter urea nitrogen from your blood and excrete it in urine. The BUN test helps doctors evaluate how well your kidneys are performing this important function.
Why Do I Need This Test?
Your doctor may order a BUN test as part of a routine health checkup or to monitor existing kidney conditions. It helps detect kidney disease or damage early, assess dehydration, monitor the effectiveness of kidney treatments, or check for other conditions that may affect kidney function such as heart failure or liver disease.
How is the Test Performed?
A healthcare professional will draw a small blood sample from a vein in your arm using a needle. The sample is then sent to a laboratory for analysis. You do not need to fast before this test, but inform your doctor about any medications or supplements you are taking, as certain drugs can affect BUN levels.
Understanding Your Results
BUN results are measured in milligrams per deciliter (mg/dL). The normal range is typically 7-20 mg/dL, though this may vary slightly between laboratories. Higher than normal BUN levels may indicate kidney problems, dehydration, heart failure, or excessive protein intake. Lower than normal levels may suggest liver disease or malnutrition. Your doctor will interpret your results in context with other tests and your overall health condition.
Reference range
Adult reference range: 7-20 mg/dL. Reference ranges may vary slightly by laboratory. Pediatric ranges: 5-18 mg/dL. Geriatric: similar to adult with slight upper limit increase.mg/dL
No fasting required. Ensure adequate hydration unless contraindicated. Inform laboratory of current medications including diuretics, corticosteroids, and NSAIDs.
Clinical interpretation
How abnormal results are interpreted and what conditions they suggest.
◆Associated findings1
Short name
BUN
Part of panels
Frequently asked questions
Do I need to fast before a BUN test?
What can cause high BUN levels besides kidney disease?
Is the BUN test painful?
How often should I have a BUN test?
Can exercise affect BUN levels?
Sources
- 1
- 2
- 3MedlinePlus - BUN TestSource
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