Blood Urea Nitrogen (BUN) Test
The BUN test measures how much urea nitrogen is in your blood, helping your doctor check how well your kidneys are filtering waste from your body.
{"BUN test measures waste product (urea) in your blood","Kidneys filter urea nitrogen from the blood","High BUN may indicate kidney problems or dehydration","Low BUN may indicate liver disease or overhydration","Results help doctors assess kidney function"}
Key facts at a glance
- LOINC
- 12963-5
- Short code
- BUN
- Synonyms
- BUN BldP-mCnc
- Category
- chemistry
- Sample
- whole-blood
- Container
- Serum separator tube (SST, gold top) or EDTA plasma tube (lavender top)
- 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
- 18–120 years
- Method
- Enzymatic (Urease) or Diacetyl Monoxime colorimetric method
- CPT
- 84520
- SNOMED
- 271244001
- Specimen volume
- 2-3 mL of whole blood
- Stability
- Room temperature: 24-48 hours; Refrigerated (2-8°C): 72 hours; Frozen (-20°C): 7 days
- Hemolysis max
- 50
- Lipemia max
- 300
- Icterus max
- 20
- TAT
- 1–4 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 body breaks down protein from foods you eat. Normally, your kidneys filter urea nitrogen out of your blood and it leaves your body through urine.
Why do I need this test?
Your doctor may order a BUN test as part of a routine blood panel or if you have symptoms of kidney problems such as swelling in your hands or feet, changes in urination patterns, fatigue, or nausea. The test helps your doctor understand how well your kidneys are filtering waste from your blood.
How is the test done?
A healthcare professional 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 do not need to fast before this test, but your doctor may ask you to avoid certain medications that could affect the results.
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 between 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 may indicate: kidney dysfunction or disease, dehydration, heart failure, gastrointestinal bleeding, or high protein intake. Certain medications like diuretics can also increase BUN levels.
Low BUN levels may indicate: liver disease, malnutrition, overhydration, or pregnancy. Low protein diets can also result in lower BUN levels.
The BUN test is often performed together 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.
Frequently asked questions
Does the BUN test hurt?
Are there any risks from this test?
How long does it take to get results?
What can I do to maintain normal BUN levels?
Can medications affect my BUN results?
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