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Blood Urea Nitrogen (BUN) Test: About Your Child's Test

Location of kidneys, with detail of the kidneys, ureter, bladder, and urethra

What is it?

A blood urea nitrogen (BUN) or urea test measures the amount of nitrogen in your child's blood that comes from the waste product urea. Urea is made in the liver. It's passed out of your child's body in the urine. If your child's kidneys can't remove urea from the blood normally, the urea level rises. Dehydration can also make your child's urea level higher.

A urea test may be done with a blood creatinine test. The level of creatinine in your child's blood also tells how well your child's kidneys are working. A high creatinine level may mean that your child's kidneys aren't working as they should. Urea and creatinine tests can be used together to find the urea-to-creatinine ratio.

Why is this test done?

A urea test is done to:

  • See if your child's kidneys are working normally.
  • See if your child's kidney disease is getting worse.
  • See if treatment of your child's kidney disease is working.
  • Check for severe dehydration. Dehydration generally causes urea levels to rise more than creatinine levels. This causes a high urea-to-creatinine ratio.

How do you prepare for the test?

Don't let your child eat a lot of meat or other protein in the 24 hours before the urea test.

How is the test done?

A health professional uses a needle to take a blood sample, usually from the arm.

What happens after the test?

  • Your child will probably be able to go home right away.
  • Your child can go back to his or her usual activities right away.

Follow-up care is a key part of your child's treatment and safety. Be sure to make and go to all appointments, and call your doctor or nurse advice line (811 in most provinces and territories) if your child is having problems. Ask your doctor when you can expect to have your child's test results.

Where can you learn more?

Go to

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