Blood Urea Nitrogen (BUN): Testing, Levels & Indication

Overview

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:

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.

Age and SexNormal BUN Level (mg/dL)Children between 1 and 17 years.Between 7 and 20 mg/dL.Adult women and people assigned female at birth.Between 6 and 21 mg/dL.Adult men and people assigned male at birth.Between 8 and 24 mg/dL.

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:

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.