BUN (Blood Urea Nitrogen) Test
Reviewed
A BUN test measures the amount of urea nitrogen in your blood. Urea nitrogen is a waste product formed when your body breaks down proteins. It is carried in your blood and removed by your kidneys when you urinate. A small amount is normal, but higher-than-normal levels may indicate that your kidneys are not working well. The test can help uncover kidney problems early, when treatment can be more effective.
Preparation and collection
Usually no special preparation is needed. If your provider has ordered other tests on the same blood sample, you may need to fast (not eat or drink) for several hours before the test. Your provider will tell you if any special instructions apply.
Understanding this test
Use the reference interval and units printed by the laboratory that performed the test. A result outside that interval is not a diagnosis by itself, and a result inside it does not rule out every condition. Your symptoms, history, medicines, timing, and related tests can change what the result means.
- A BUN test is only one type of measurement of kidney function. If your provider thinks you may have kidney disease, you may need other tests (e.g., creatinine, GFR).
- Abnormal results do not always mean you have a medical condition that needs treatment.
- BUN levels can vary according to your sex and usually increase with age.
What to do next
To learn what your results mean, talk to your provider. If your provider thinks you may have kidney disease, you may need other tests such as creatinine or GFR (glomerular filtration rate).
Evidence source
U.S. National Library of Medicine: BUN (Blood Urea Nitrogen) Test