Blood Urea Nitrogen (BUN) Test

Overview

What is the blood urea nitrogen (BUN) test?

A blood urea nitrogen (BUN) test measures the amount of urea nitrogen in your blood. Levels of urea nitrogen is one marker on how well your kidneys are working. This is a simple test done by drawing blood out of your body through a vein in your arm.

Urea is a waste product formed in the liver that travels through your blood to the kidneys, which then filters it out of the blood. It is then carried out of your body through urine. A small amount of urea in your blood is normal because this process is ongoing. Too much urea shows that it is not being filtered out properly and may indicate a possible problem with the kidneys.

Why is blood urea nitrogen (BUN) test done?

A BUN test is a routine test ordered by your doctor during your checkup as part of a comprehensive metabolic panel (CMP) or basic metabolic panel (BMP). It will be done if you are admitted to an emergency room or during a regular hospital stay.

The BUN test may also be ordered as a precaution if you have risk factors for kidney disease. Early kidney disease doesn’t have symptoms, but the following factors can put you at higher risk:

The BUN test is often ordered if the doctor suspects your symptoms are signs of kidney disease. These include:

  • Fatigue
  • Frequent urination or not often enough
  • Urine that is discolored or unusual (bloody, foamy, coffee-colored)
  • Swelling around the eyes or on the face, belly, arms, legs, or feet
  • High blood pressure
  • Nausea or vomiting

Test Details

What happens during a blood urea nitrogen (BUN) test?

The BUN test is a simple blood draw and very little risk is involved. You will sit in a chair and a healthcare professional will insert a thin needle into your arm and draw blood into small vials. You may feel a little prick and the area may bruise slightly afterward. Any marks left by the injection go away quickly. A bandage taped over the spot can be removed a few hours later.

How do I prepare for the blood urea nitrogen (BUN) test?

There is nothing you need to do to prepare for the BUN test. However, many times your doctors will order other blood tests that do require you to fast (not eat or drink) in addition to the BUN tests. Ask your doctor if you need to fast before getting your blood work.

Results and Follow-Up

What do the results of the blood urea nitrogen (BUN) test mean?

Normal BUN levels vary, but high levels in your blood sample usually mean your kidneys aren’t working normally. They can be a sign of kidney disease or failure. Higher than normal BUN levels may also indicate dehydration, high-protein diet, medications, burns or other conditions. Your doctor tell you what your results mean.

Low urea levels are not common and rarely a cause for concern. They can represent a low protein diet or small body type.

Last reviewed by a Cleveland Clinic medical professional on 01/10/2018.

References

  • Lab Tests Online. Blood Urea Nitrogen. (https://labtestsonline.org/understanding/analytes/bun/tab/test/) Accessed 2/13/2018.
  • US National Library of Medicine. BUN (Blood Urea Nitrogen). (https://medlineplus.gov/labtests/bunbloodureanitrogen.html) Accessed 2/13/2018.
  • National Heart, Lung and Blood Institute. Types of Blood Tests. (https://www.nhlbi.nih.gov/health/health-topics/topics/bdt/types) Accessed 2/13/2018.

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