Health Encyclopedia

Blood Urea Nitrogen

Does this test have other names?

Urea nitrogen, BUN, serum BUN

What is this test?

A blood urea nitrogen (BUN) test measures the amount of urea nitrogen found in your blood. BUN levels help your healthcare provider see how well your kidneys are working. The test may be used along with other measurements to help diagnose a kidney disorder or find out how well your treatment for kidney disease is working. 

Why do I need this test?

If your healthcare provider suspects that you have kidney problems, he or she may order a BUN test to help diagnose the condition. Symptoms that can mean kidney problems include:

  • Needing to urinate more or less often

  • Joint or bone pain

  • Muscle cramps

  • Restless legs while you're trying to sleep

  • Fatigue

  • Itchiness

  • Swelling in the arms or legs

Many people with kidney problems may not have symptoms right away. 

Your healthcare provider might order a BUN test for other reasons. Depending on your overall health, it may be part of a routine health check to find out how your kidneys are working. If you need dialysis or medicine for kidney function, your provider might order the test to check the health of your kidneys before the procedure, after the procedure, or both. BUN tests are also routine during hospital stays for certain conditions. 

What other tests might I have along with this test?

Your healthcare provider may also check the creatinine levels in your blood. On its own, the BUN level does little to tell your provider for sure about your kidney (renal) function. But when it is measured along with creatinine levels, your provider can look at how these two levels compare to help find out your kidney function. If this ratio is higher or lower than normal, you may have some type of kidney problem.

If your healthcare provider suspects you may have a kidney problem, he or she may also order other blood and urine tests, as well as check your blood pressure, to help find out your kidney function. 

What do my test results mean?

Many things may affect your lab test results. These include the method each lab uses to do the test. Even if your test results are different from the normal value, you may not have a problem. To learn what the results mean for you, talk with your healthcare provider.

The normal BUN level is between about 7 and 21 milligrams per deciliter (mg/dL). Unless this level is greater than 60 mg/dL, though, it may not help your healthcare provider measure your kidney health.

A better measure is the ratio of BUN to creatinine found in your blood. Typically, the ratio of BUN to creatinine should be between 10:1 and 20:1. If it's lower or higher than that, it may mean you have a problem with your kidneys. 

How is this test done?

The test requires a blood sample, which is drawn through a needle from a vein in your arm.

Does this test pose any risks?

Taking a blood sample with a needle carries risks that include bleeding, infection, bruising, or feeling dizzy. When the needle pricks your arm, you may feel a slight stinging sensation or pain. Afterward, the site may be slightly sore. 

What might affect my test results?

A high-protein diet, steroid use, dehydration, burn injuries, and advancing age are some of the many reasons why your BUN levels might rise even if your kidneys are working as they should. This is why the ratio of BUN levels to creatinine levels is a more reliable measure of kidney health.

How do I get ready for this test?

You don't need to prepare for this test. 


Medical Reviewers:

  • Moloney Johns, Amanda, PA-C, MPAS, BBA
  • Walton-Ziegler, Olivia, MS, PA-C