Blood Urea Nitrogen (BUN) Test

What is a blood urea nitrogen test?

A blood urea nitrogen (BUN) test measures the amount of urea nitrogen in your blood.

Urea nitrogen is a waste product. It develops when your body breaks down the protein in the foods you eat. It forms in your liver and travels through your blood to your kidneys, which then filter it out of your blood. It leaves your body through your urine (pee).

Urea nitrogen levels in your blood are one marker that allows healthcare providers to understand how well your kidneys are working. A small amount of urea nitrogen in your blood is normal. If you have too much urea nitrogen in your blood, your kidneys aren’t filtering it properly. You may have a condition that’s affecting your kidneys’ health.

Why is a blood urea nitrogen test done?

A healthcare provider may recommend a BUN test during a checkup as part of a comprehensive metabolic panel (CMP) or basic metabolic panel (BMP) blood test.

A provider may also recommend a BUN test if you have a higher risk of kidney disease. The early stages of kidney disease don’t have any symptoms, but the following factors may put you at a higher risk:

• Biological family history of kidney disease.
• Diabetes.
• High blood pressure (hypertension).
• Heart disease.

If you have symptoms of later-stage kidney disease, it’s a good idea to get a BUN test. Symptoms of later-stage kidney disease may include:

• A need to pee more than usual.
• Foamy pee.
• Blood in your pee.
• Fatigue.
• Loss of appetite.
• Swelling, particularly in your hands, feet and ankles.

What is a normal blood urea nitrogen level?

A normal blood urea nitrogen level varies according to your age and sex.

What level of urea indicates kidney failure?

Healthcare providers don’t use BUN to define kidney failure. However, if your BUN numbers are higher than your baseline, and if your creatinine (a waste product from muscle tissue breakdown) is also high, then kidney failure is likely.

What does high blood urea nitrogen mean?

High BUN levels may suggest that your kidneys aren’t working as they should. However, even if your kidneys are working properly, you may have elevated BUN levels from the following:

• High-protein diet.
• Dehydration.
• Aging (infants and children have lower BUN levels).
• Certain medications, including carbamazepine, methotrexate and tetracycline.
• Burns.
• Blockage in your urinary system that prevents you from peeing.
• Stress.
• Heart attack.
• Gastrointestinal (GI) bleeding.

What does low blood urea nitrogen mean?

Low BUN levels aren’t common. However, you may have low BUN levels from the following:

• Low-protein diet.
• Small body type.
• Overhydration (too much water in your body).
• Liver disease.

What happens before a blood urea nitrogen test?

Tell your healthcare provider if you have a bleeding disorder or are taking blood-thinning medications before a BUN test. Your healthcare provider may recommend other blood tests in addition to a BUN test. Other blood tests may require you to fast (not eat or drink) for eight to 12 hours before the test. Ask your healthcare provider if you need to fast before a BUN test or any other type of blood test.

What happens during a blood urea nitrogen test?

A healthcare provider can measure your BUN levels through a blood test.

• They’ll disinfect the skin around a vein in your arm with iodine, isopropyl alcohol or another skin cleaner.
• They’ll then use a thin needle (slightly smaller than the size of a standard earring post) to withdraw blood from a vein in your arm into small vials. You may feel a slight pinch, and the affected area may bruise afterward. However, any marks from the needle go away quickly.
• They’ll then send your blood sample to a lab for analysis. It may take one to three days to get your results.

What happens after a blood urea nitrogen test?

Once the lab finishes testing your blood sample, a healthcare provider will contact you to explain your test results and answer any questions. If your provider suspects you have kidney disease, they may order additional tests, including:

• Serum creatinine. This test looks for the buildup of creatinine.
• Estimated glomerular filtration rate (eGFR). This is a value that a provider calculates from the amount of creatinine in your blood to get an estimate of how well your kidneys clean your blood. It calculates the filtration rates according to your protein levels, age, sex, size and race.

How do you fix high BUN levels?

Healthcare providers don’t “fix” high BUN levels. They find out why someone’s kidney function isn’t normal and address the problem. However, the easiest way to reduce high BUN levels is to make changes to your diet.

If you don’t have kidney disease and aren’t on kidney dialysis, you should make sure to drink more fluids — an isolated rise in BUN while your serum creatinine is relatively low could indicate dehydration. Men and people assigned male at birth should drink approximately 13 cups (3 liters) of fluids each day. Women and people assigned female at birth should drink approximately 9 cups (2.2 liters) of fluids each day.

A low-protein diet can also help reduce high BUN levels. Healthy low-protein foods include:

• Grains: Oats, rice and pasta.
• Fruits: Apples, berries and bananas.
• Vegetables: Leafy greens, peppers and broccoli.
• Healthy fats: Avocados, nuts and coconut oil.

What foods should I avoid if my blood urea nitrogen levels are high?

If your BUN levels are high, it’s a good idea to avoid or limit high-protein foods. Examples of high-protein foods include:

• Meats: Beef, chicken, pork and salmon.
• Dairy: Milk, cheese and yogurt.

Most people should consume between 40 and 60 grams (g) of protein each day. However, you may need to reduce your protein consumption by as much as half if you have high BUN levels.

What medications are used to treat abnormal blood urea nitrogen levels?

Healthcare providers don’t typically prescribe medications to treat abnormal BUN levels.

When should I see a healthcare provider?

Contact your healthcare provider if you haven’t heard from them with your BUN test results after several days.

What questions should I ask a healthcare provider?

• What do my test results mean?
• Do you recommend any other tests?
• How do I lower my BUN levels?
• Is a health condition causing my abnormal BUN levels?

A note from Cleveland Clinic

Urea nitrogen is a waste product that forms in your liver after your body breaks down protein. Sometimes, your blood has too much or too little urea nitrogen, which can cause health problems. If you have symptoms of high or low urea nitrogen in your blood, you should talk to a healthcare provider. They can order a blood urea nitrogen (BUN) test to see how well your kidneys work and recommend the proper treatment.