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Blood Urea Nitrogen (BUN) Test: About This Test

Kidneys, ureters, bladder

What is it?

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

A urea test may be done with a blood creatinine test. The level of creatinine in your blood also tells how well your kidneys are working. A high creatinine level may mean your kidneys are not working properly. 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 kidneys are working normally.
  • See if your kidney disease is getting worse.
  • See if treatment of your 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. Kidney disease or blockage of the flow of urine from your kidney causes both urea and creatinine levels to go up.

How do you prepare for the test?

Do not eat a lot of meat or other protein in the 24 hours before having a 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?

  • You will probably be able to go home right away.
  • You can go back to your usual activities right away.

Follow-up care is a key part of your 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 you are having problems. It's also a good idea to keep a list of the medicines you take. Ask your doctor when you can expect to have your test results.

Where can you learn more?

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