BUN (Blood Urea Nitrogen)

A BUN, or blood urea nitrogen test, measures the amount of urea nitrogen in your blood. Urea nitrogen is a waste product that forms as your body breaks down proteins. It's carried in your blood and then removed by your kidneys when you urinate (pee).

Having a small amount of urea nitrogen in your blood is normal. But higher-than-normal BUN levels may be a sign that your kidneys aren't working well. If you have kidney disease, this waste material can build up in your blood and may lead to serious health problems, including high blood pressure, anemia, and heart disease.

People with early kidney disease may not have any symptoms. A BUN test can help uncover kidney problems early, when treatment can be more effective. Other names for a BUN test: Urea nitrogen test, serum BUN, BUN to Creatinine Ratio

Why this test is done

Your health care provider may order a BUN test:

• As part of a routine checkup
• To monitor the treatment of a kidney disease
• For screening if you are at risk of a kidney problem, since early kidney disease usually does not have any signs or symptoms. You may be at risk of developing a kidney problem because of:
• A family history of kidney problems
• Diabetes
• High blood pressure
• Heart disease
• Obesity
• Being over the age of 60
• Smoking or using other tobacco products

Your provider may also check your BUN levels if you are having symptoms of later-stage kidney disease, which can include:

• Needing to go the bathroom (urinate) frequently or infrequently
• Itching
• Fatigue
• Swelling in your arms, legs, or feet
• Muscle cramps
• Trouble sleeping

How to prepare

Usually, no special preparation is necessary for a BUN test. But if your provider has ordered other tests on your blood sample, you may need to fast (not eat or drink) for several hours before the test. Your provider will let you know if there are any special instructions.

Sample type

Blood