Patient education: Blood urea nitrogen test (The Basics)

What is a blood urea nitrogen test? — A blood urea nitrogen, or "BUN" test, is a type of blood test. It measures the amount of a substance called "urea nitrogen" in the blood. Urea nitrogen is a waste product made by the body. When the kidneys work properly, they filter urea nitrogen out of the blood.

A high BUN level can be caused by:

●Eating a high-protein diet

●Breakdown of body tissue that can happen with an infection or serious injury

●Losing a lot of salt and water, for example, through vomiting or diarrhea

●Problems with the kidneys

The BUN test by itself is not a good way to tell if you have kidney problems. A test called "creatinine" is a better test to check your kidneys. Creatinine is another waste product made by the body. It is measured along with the BUN. A high level of creatinine in your blood usually means that you have a problem with your kidneys.

BUN and creatinine might both be measured as part of a blood test called a "renal function panel." A renal function panel measures the amount of a few different substances in the blood to see how well the kidneys are working.

Why might I get a BUN test? — Your doctor might want to measure your BUN if your results on a different type of blood test were abnormal.

How do I prepare for a BUN test? — For this test, you need to get a "blood draw." Your doctor or nurse will tell you where to go for this.

It might help to wear a short-sleeve shirt to your blood draw appointment. This makes it easier for the person drawing the blood to get to your arm.

What happens during a blood draw? — For the blood draw, a needle is used to take a small amount of blood from your arm (figure 1). Collecting the blood only takes a few minutes. The blood is then tested in a lab.

Tell the person who takes your blood:

●If you take "blood thinner" medicines or if you have a bleeding problem – They will make sure that your bleeding is under control before you leave.

●If you have a latex allergy – Some of the supplies used for blood draws might contain latex.

●If you have a preferred arm to use

Most of the time, getting blood taken does not cause problems. You might have a little soreness or bruising where the needle went in.

What do my results mean? — Your doctor or nurse will tell you when to expect your results, and will contact you with the results. Or if you use an online "patient portal," you might get an alert there when your results are ready.

If your BUN test shows any abnormal results, your doctor or nurse will talk to you about what to do next. They might need to do more tests to figure out what the cause is.

If you do have a health problem, your doctor will work with you to come up with a treatment plan.

More on this topic

Patient education: Renal function panel (The Basics)
Patient education: Serum creatinine test (The Basics)