BUN (Blood Urea Nitrogen) Test

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KEY POINTS

• The blood urea nitrogen test is a common test to check how well your child’s kidneys are working. It measures the amount of urea nitrogen in the blood. The kidneys filter the urea nitrogen out of the blood and into the urine.
• A small amount of blood is taken from a vein in your child’s arm with a needle. In younger children, this test can be done with a finger prick or heel stick. The blood is collected in tubes and sent to a lab.
• Talk to your child’s healthcare provider about what the test results mean and ask any questions you have.

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What is the BUN test?

The blood urea nitrogen (BUN) test is a common test to check how well your child’s kidneys are working. It measures the amount of urea nitrogen in your child’s blood. Nitrogen is a chemical made by the body when food is digested. It combines with other things to form urea, which is body waste that is carried by the blood to the kidneys. The kidneys filter the urea nitrogen out of the blood and into the urine.

Why is it done?

This test is done to help diagnose kidney problems or to check how well treatment of kidney disease is working.

Some medicines are processed by the kidneys and can cause kidney damage as a side effect. Some medical conditions can also cause kidney damage. The BUN test may be done to be sure your child has normal kidney function before your child starts taking these medicines or to check the effect of the medical condition on the kidneys.

This test is almost always done with another test called the creatinine test. Creatinine is a waste product that is made when another chemical, creatine, is broken down to produce energy for the muscles. This waste product is carried by the blood to the kidneys, which filter it from the body into the urine.

How do I prepare my child for this test?

Your child may need to avoid taking certain medicines before the test because they might affect the test result. Tell your child's healthcare provider about all the medicines and supplements your child takes. Ask your provider before stopping any of your child’s regular medicines.

Talk to your child’s healthcare provider if you have any questions.

How is the test done?

Having this test will take just a few minutes. A small amount of blood is taken from a vein in your child’s arm with a needle. In younger children, this test can be done with a finger prick or heel stick.

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

What does the test result mean?

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

• Your child’s kidneys aren't working well.
• Your child has not been drinking enough liquids to replace liquids lost, for example through sweat or urine.
• Your child has been eating high-protein food and drinks.
• Your child is taking a medicine that affects the BUN level.
• Your child has bleeding into the stomach or intestine such as from an ulcer.
• Your child has heart failure.
• Your child is in shock from burns or an accident.
• Your child has something blocking the flow of urine such as a growth inside the belly or some problem your child had at birth.

If your child is not sick, a BUN level lower than normal is usually not a cause for concern. If the BUN is lower than normal, it may mean:

• Your child is drinking a lot more liquids than are needed to replace liquids lost through sweat or urine.
• Your child is not getting the nutrients the body needs.
• Your child has very little muscle mass.
• Your child’s liver isn't working well.

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 healthcare provider about your child’s result and ask questions such as:

• If your child needs more tests
• What kind of treatment your child may need
• What lifestyle, diet, or other changes your child might need to make