BUN (Blood Urea Nitrogen) Test
Reviewed
Also called: Urea nitrogen test, serum BUN, BUN to Creatinine Ratio
A BUN test measures the amount of urea nitrogen in your blood. Urea nitrogen is a waste product formed when your body breaks down proteins. It is carried in your blood and removed by your kidneys when you urinate. A small amount is normal, but higher-than-normal levels may indicate that your kidneys are not working well. The test can help uncover kidney problems early, when treatment can be more effective.
Specimen: blood
Why this test may be ordered
- As part of a routine checkup
- To monitor treatment of kidney disease
- For screening if you are at risk of a kidney problem (e.g., family history, diabetes, high blood pressure, heart disease, obesity, age over 60, smoking)
Preparation and collection
Usually no special preparation is needed. If your provider has ordered other tests on the same blood sample, you may need to fast (not eat or drink) for several hours before the test. Your provider will tell you if any special instructions apply.
A health care professional will take a blood sample from a vein in your arm using a small needle. After the needle is inserted, a small amount of blood is collected into a test tube or vial. The procedure usually takes less than five minutes.
There is very little risk to having a blood test. You may experience slight pain or bruising at the spot where the needle was put in, but most symptoms go away quickly.
Understanding results
Normal BUN levels can vary. Abnormal results do not always mean you have a medical condition that needs treatment. BUN levels can vary according to your sex and usually increase with age. To learn what your results mean, talk to your provider.
- Higher than normal: May be a sign that your kidneys are not working well. Other possible reasons include dehydration, burns, certain medicines, a high-protein diet, or a recent heart attack. Limitation: Abnormal results do not always mean you have a medical condition that needs treatment. BUN levels can vary according to your sex and usually increase with age. Next step: Talk to your provider to learn what your results mean. You may need other tests such as creatinine or GFR (glomerular filtration rate) to assess kidney function.
- Lower than normal: Possible reasons include a lack of protein in your diet, malnutrition, or liver disease. Limitation: Abnormal results do not always mean you have a medical condition that needs treatment. BUN levels can vary according to your sex and usually increase with age. Next step: Talk to your provider to learn what your results mean. You may need other tests such as creatinine or GFR to assess kidney function.
- A BUN test is only one type of measurement of kidney function. If your provider thinks you may have kidney disease, you may need other tests (e.g., creatinine, GFR).
- Abnormal results do not always mean you have a medical condition that needs treatment.
- BUN levels can vary according to your sex and usually increase with age.
What to do next
To learn what your results mean, talk to your provider. If your provider thinks you may have kidney disease, you may need other tests such as creatinine or GFR (glomerular filtration rate).
- What do my BUN results mean for my kidney health?
- Do I need any follow-up tests based on my BUN level?
- What can I do to keep my kidneys healthy?
Evidence source
U.S. National Library of Medicine: BUN (Blood Urea Nitrogen) Test