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BUN (Blood Urea Nitrogen)

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 and may lead to serious health problems, including high blood pressure, anemia, and heart disease.

The test measures the amount of urea nitrogen in your blood. Urea nitrogen is one of the waste products removed from your blood by your kidneys. Higher than normal BUN levels may be a sign that your kidneys aren't working efficiently.

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, and can be used to 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. Although early kidney disease usually does not have any signs or symptoms, certain factors can put you at a higher risk. These include:

  • Family history of kidney problems
  • Diabetes
  • High blood pressure
  • Heart disease

In addition, your BUN levels may be checked if you are experiencing symptoms of later stage kidney disease, such as:

  • Needing to go the bathroom (urinate) frequently or infrequently
  • Itching
  • Recurring fatigue
  • Swelling in your arms, legs, or feet
  • 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?

You don't need any special preparations for a BUN test. If your health care provider has also ordered other blood tests, you may need to fast (not eat or drink) for several hours before the test. Your health care 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 have 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 correctly. However, abnormal results don't always indicate that you have a medical condition needing treatment. Higher than normal BUN levels can also be caused by dehydration, burns, certain medications, a high protein diet, or other factors. To learn what your results mean, talk to your health care provider.

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 health care provider suspects you have kidney disease, additional tests may be recommended. These may include a measurement of creatinine, which is another waste product filtered by your kidneys, and a test called a GFR (Glomerular Filtration Rate), which estimates how well your kidneys are filtering blood.

References

  1. 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
  2. Mayo Clinic [Internet]. Mayo Foundation for Medical Education and Research; c1998-2017. Blood Urea Nitrogen (BUN) Test: Overview; 2016 Jul 2 [cited 2017 Jan 30]; [about 3 screens]. Available from: http://www.mayoclinic.org/tests-procedures/blood-urea-nitrogen/home/ovc-20211239
  3. Mayo Clinic [Internet]. Mayo Foundation for Medical Education and Research; c1998-2017. Blood Urea Nitrogen (BUN) Test: Results; 2016 Jul 2 [cited 2017 Jan 30]; [about 7 screens]. Available from: http://www.mayoclinic.org/tests-procedures/blood-urea-nitrogen/details/results/rsc-20211280
  4. Mayo Clinic [Internet]. Mayo Foundation for Medical Education and Research; c1998-2017. Chronic Kidney Disease; 2016 Aug 9; [cited 2017 Jan 30]; [about 3 screens]. Available from: http://www.mayoclinic.org/diseases-conditions/chronic-kidney-disease/symptoms-causes/dxc-20207466
  5. National Heart, Lung, and Blood Institute [Internet]. Bethesda (MD): U.S. Department of Health and Human Services; Types of Blood Tests; [updated 2012 Jan 6; cited 2017 Jan 30]; [about 5 screens]. Available from: https://www.nhlbi.nih.gov/health/health-topics/topics/bdt/types
  6. National Heart, Lung, and Blood Institute [Internet]. Bethesda (MD): U.S. Department of Health and Human Services; What Are the Risks of Blood Tests? [updated 2012 Jan 6; cited 2017 Jan 30]; [about 5 screens]. Available from: https://www.nhlbi.nih.gov/health/health-topics/topics/bdt/risks
  7. National Heart, Lung, and Blood Institute [Internet]. Bethesda (MD): U.S. Department of Health and Human Services; What To Expect with Blood Tests; [updated 2012 Jan 6; cited 2017 Jan 30]; [about 5 screens]. Available from: https://www.nhlbi.nih.gov/health/health-topics/topics/bdt/with
  8. National Institute of Diabetes and Digestive and Kidney Diseases [Internet]. Bethesda (MD): U.S. Department of Health and Human Services; Kidney Disease Basics; [updated 2012 Mar 1; cited 2017 Jan 30]; [about 7 screens]. Available from: https://www.niddk.nih.gov/health-information/health-communication-programs/nkdep/learn/causes-kidney-disease/kidney-disease-basics/pages/kidney-disease-basics.aspx
  9. 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/health-information/health-communication-programs/nkdep/a-z/explaining-kidney-test-results/documents/kidney-test-results-508.pdf
  10. National Kidney Foundation [Internet]. New York: National Kidney Foundation Inc., c2016. About Chronic Kidney Disease; [cited 2017 Jan 30]; [about 3 screens]. Available from: https://www.kidney.org/kidneydisease/aboutckd

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