BUN (Blood Urea Nitrogen) Test

What is the BUN test?

The blood urea nitrogen (BUN) test is a test of how well your child’s kidneys are working. It measures the amount of nitrogen in your child’s blood. The nitrogen is present in a chemical called urea. Urea is a waste product produced as your child’s body digests protein. Urea is carried by the blood to the kidneys, which filter the urea out of the blood and into the urine.

Why is this test done?

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 your child is 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 your child has normal kidney function before your child start taking these medicines.

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

How do I prepare my child for this test?

Your child may need to avoid taking certain medicines before the test. Some medicines can cause BUN to be higher than normal. Make sure your child’s healthcare provider knows about any medicines, herbs, or supplements that your child is taking. Don't stop any of your child’s regular medicines without first talking to your child’s provider about it.

How is the test done?

The skin on your child’s arm is cleaned very well and then a small amount of blood is taken from a vein in your child’s arm with a needle. The blood is collected in tubes and sent to a lab. In younger children, this test can be done with a finger prick or heel stick.

Having this test will take just a few minutes. There is no risk of getting AIDS, hepatitis, or any other blood-borne disease from this test.

What does the test result mean?

The normal range for BUN in children over 2 years of age is 5 to 20 milligrams per deciliter (mg/dL). For children under 2, the range is 4 to 15 mg/dl. The normal range may vary slightly from lab to lab. Normal ranges are usually shown next to your child’s results in the lab report.

Your child’s BUN level may be higher than normal because:

• Your child’s kidneys aren't working well.
• Your child is dehydrated (low levels of fluid in the body).
• Your child has eating a high-protein diet.
• Your child is bleeding into your child’s stomach or intestine (from an ulcer, for example).
• Your child’s heart is not delivering enough blood to the rest of the body.
• Your child is in shock from burns or an accident.
• Your child’s urinary tract is blocked (for instance, from mass inside the abdomen or from some problem your child was born with).

If your child is not sick, a BUN level lower than normal is, in general, not cause for concern. If your child seems sick, and your child’s BUN level is lower than normal, it may mean:

• Your child’s liver isn't working well.
• Your child has been eating a low-protein diet.
• Your child has been malnourished.
• Your child has been drinking a lot of fluids.
• Your child has very little muscle mass.

What if my child’s test result is not normal?

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

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

• if your child needs additional tests
• what kind of treatment your child might need
• when your child needs to be tested again.