BUN (Blood Urea Nitrogen) Test

What is the BUN test?

The BUN test is a test of how well your kidneys are working. It measures the amount of nitrogen in your blood. The nitrogen is present in a chemical called urea. Urea is a waste product your body makes when you digest food. Urea is carried by the blood to the kidneys, which filter the urea out of the blood and into the urine.

Another name for this test is blood urea nitrogen test.

Why is this test done?

This test is usually done to see how well your kidneys are working. Kidney disease often makes it hard for the kidneys to filter as much urea as they should. This causes high levels of urea in the blood. This test is also done if you are having kidney dialysis to see how well the dialysis is working.

Some medicines are processed by the kidneys or can cause kidney damage as a side effect. The BUN test may be done to be sure you have normal kidney function before you start taking these medicines.

This test is almost always done with another test called the creatinine test.

How do I prepare for this test?

• You may need to avoid taking certain medicines before the test because they might affect the test result. Make sure your healthcare provider knows about any medicines, herbs, or supplements that you are taking. Don't stop any of your regular medicines without first talking to your healthcare provider about it.

How is the test done?

A small amount of blood is taken from your arm with a needle. The blood is collected in tubes and sent to a lab.

Having this test will take just a few minutes of your time.

How will I get the test result?

Ask your healthcare provider when and how you will get the result of your test.

What does the test result mean?

The normal range for BUN is 7 to 20 milligrams per deciliter (mg/dL). The normal range may vary slightly from lab to lab. Normal ranges are usually shown next to your results in the lab report.

Your BUN level may be higher than normal because:

• Your kidneys are not working well.
• You are dehydrated (low levels of fluid in your body).
• You have been eating a high-protein diet.
• You have bleeding into your stomach or intestine (from an ulcer, for example).
• You have heart failure or you have had a heart attack.
• You are in shock from burns or an accident.
• Your urinary tract is blocked (for example, from a kidney stone or tumor, or from an enlarged prostate in men).
• You are taking a medicine that affects your BUN level.

If you are not sick, a BUN level lower than normal is, in general, not a cause for concern. If you are sick and your BUN is lower than normal, it may mean:

• Your liver isn't working well.
• You are not getting the nutrients your body needs.

What if my test result is not normal?

Test results are only one part of a larger picture that takes into account your medical history and current health. Sometimes a test needs to be repeated to check the first result. Talk to your health care provider about your result and ask questions.

If your test result is not normal, ask your healthcare provider:

• if you need additional tests
• what treatment you may need
• when you need to be tested again.