BUN (Blood Urea Nitrogen) Test
Reviewed
Also called: Urea nitrogen test, serum BUN, BUN to Creatinine Ratio
A BUN, or blood urea nitrogen test, measures the amount of urea nitrogen in your blood.
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 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.
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 will be collected into a test tube or vial. You may feel a little sting when the needle goes in or out. This 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
BUN levels can vary according to your sex. They also usually increase with age.
What does high BUN (blood urea nitrogen) mean?
Higher than normal: Normal BUN levels can vary, but generally, a high blood urea nitrogen level is a sign that your kidneys are not working well. Limitation: A few other reasons your BUN level might be higher than normal include: Dehydration (too little fluid in your body), Burns, Certain medicines. Next step: If your provider thinks you may have kidney disease, you may need other tests.- Lower than normal: A few other reasons your BUN levels might be lower than normal include: A lack of protein in your diet, Malnutrition, Liver disease. Limitation: But abnormal results don't always mean that you have a medical condition that needs treatment. Next step: To learn what your results mean, talk to your provider.
- 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.
- 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
Source: U.S. National Library of Medicine (MedlinePlus). Practices and reference ranges may differ in your country.
U.S. National Library of Medicine: BUN (Blood Urea Nitrogen) Test