What is a BUN (Blood Urea Nitrogen) Test?
A BUN, or blood urea nitrogen test, can provide important information about your kidney function. The main job of your kidneys is to remove waste and extra fluid from your body. If you have kidney disease, this waste material can build up in your blood. Over time, this may lead to serious health problems, including high blood pressure, anemia, and heart disease.
The BUN test measures the amount of urea nitrogen in your blood. Urea nitrogen is a waste product that your kidneys remove from your blood. Higher than normal BUN levels may be a sign that your kidneys aren't working well.
People with early kidney disease may not have any symptoms. A BUN test can help uncover kidney problems at an early stage when treatment can be more effective.
Other names for a BUN test: Urea nitrogen test, serum BUN
What is it used for?
A BUN test is often part of a series of tests called a comprehensive metabolic panel. It can help diagnose or monitor a kidney disease or disorder.
Why do I need a BUN test?
Your health care provider may order a BUN test as part of a routine check-up or if you have or are at risk for a kidney problem. Early kidney disease usually does not have any signs or symptoms. You may be more likely to develop kidney disease if you have:
- Family of kidney problems
- High blood pressure
- Heart disease
Your provider may check your BUN levels if you are having symptoms of later stage kidney disease, such as:
- Needing to urinate (pee) more often or less often than usual
- Swelling in your legs, feet, or ankles
- Muscle cramps
- Trouble sleeping
What happens during a BUN test?
A health care professional will take a blood sample from a vein in your arm, using a small needle. After the needle is inserted, a small amount of blood will be collected into a test tube or vial. You may feel a little sting when the needle goes in or out. This usually takes less than five minutes.
Will I need to do anything to prepare for the test?
Usually there is no special preparation necessary for a BUN test. But if your provider has ordered other tests on your blood sample, you may need to fast (not eat or drink) for several hours before the test. Your provider will let you know if there are any special instructions to follow.
Are there any risks to the test?
There is very little risk to having a blood test. You may experience slight pain or bruising at the spot where the needle was put in, but most symptoms go away quickly.
What do the results mean?
Normal BUN levels can vary, but generally a high level of blood urea nitrogen is a sign that your kidneys are not working well. But abnormal results don't always mean that you have a medical condition that needs treatment.
Higher than normal BUN levels can also be caused by dehydration (too little fluid in your body), burns, certain medicines, a high protein diet, or other factors, including your age. BUN levels normally increase as you get older. To learn what your results mean, talk to your health care provider.
Learn more about laboratory tests, reference ranges, and understanding results.
Is there anything else I need to know about a BUN test?
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. These may include tests to measure:
- Creatinine, which is another waste product that your kidneys remove from your body
- GFR (Glomerular Filtration Rate), which estimates how well your kidneys are filtering blood
- Testing.com [Internet]. Seattle (WA): OneCare Media; c2022. Blood Urea Nitrogen;; [modified 2021 Nov 9; cited 2021 Dec 31]; [about 8 screens]. Available from: https://www.testing.com/tests/blood-urea-nitrogen-bun/
- Lyman JL. Blood urea nitrogen and creatinine. Emerg Med Clin North Am [Internet]. 1986 May 4 [cited 2017 Jan 30]; 4(2):223–33. Available from: https://www.ncbi.nlm.nih.gov/pubmed/3516645
- Mayo Clinic [Internet]. Mayo Foundation for Medical Education and Research; c1998-2022. Blood Urea Nitrogen (BUN) Test; [cited 2021 Dec 31]; [about 3 screens]. Available from: http://www.mayoclinic.org/tests-procedures/blood-urea-nitrogen/home/ovc-20211239
- Mayo Clinic [Internet]. Mayo Foundation for Medical Education and Research; c1998-2022. Chronic Kidney Disease; [cited 2021 Dec 31]; [about 3 screens]. Available from: https://www.mayoclinic.org/diseases-conditions/chronic-kidney-disease/symptoms-causes/syc-20354521
- National Heart, Lung, and Blood Institute [Internet]. Bethesda (MD): U.S. Department of Health and Human Services; Blood Tests [; cited 2021 Dec 31]; [about 19 screens]. Available from: https://www.nhlbi.nih.gov/health-topics/blood-tests
- National Institute of Diabetes and Digestive and Kidney Diseases [Internet]. Bethesda (MD): U.S. Department of Health and Human Services; Kidney Disease; [cited 2021 Dec 31]; [about 7 screens]. Available from: https://www.niddk.nih.gov/health-information/kidney-disease
- National Institute of Diabetes and Digestive and Kidney Diseases [Internet]. Bethesda (MD): U.S. Department of Health and Human Services; National Kidney Disease Education Program: Your Kidney Test Results; [updated 2013 Feb; cited 2017 Jan 30]; [about 3 screens]. Available from: https://www.niddk.nih.gov/-/media/Files/Health-Information/Health-Professionals/Kidney-Disease/Your_Kidney_Test_Results_EN.pdf
- National Kidney Foundation [Internet]. New York: National Kidney Foundation Inc., c2022. About Chronic Kidney Disease; [cited 2017 Jan 30]; [about 3 screens]. Available from: https://www.kidney.org/kidneydisease/aboutckd
- National Kidney Foundation [Internet]. New York: National Kidney Foundation Inc., c2022. Understanding Lab Values; [cited 2017 Jan 30]; [about 2 screens]. Available from: https://www.kidney.org/kidneydisease/understandinglabvalues
- University of Rochester Medical Center [Internet]. Rochester (NY): University of Rochester Medical Center; c2022. Health Encyclopedia: Blood Urea Nitrogen; [cited 2017 Jan 30]; [about 3 screens]. Available from: https://www.urmc.rochester.edu/encyclopedia/content.aspx?contenttypeid=167&contentid=urea_nitrogen_serum