What Is BUN in a Blood Test?

A blood urea nitrogen, or BUN, test is used to gauge the amount of nitrogen in the blood of a person. It also helps to understand how well the liver and kidneys are functioning, as stated by the Mayo Clinic.

If the urea nitrogen levels are high in the blood, it shows that the kidneys are not functioning properly. A person is advised not to consume a lot of meat or other protein-rich food 24 hours prior the test. A BUN test may be conducted together with a creatinine test. According to WebMD, the amount of creatinine in the body also helps to ascertain if the kidneys are functioning properly. Both tests are used to determine the BUN-to-creatinine ratio, which helps to check for conditions, such as dehydration.

To perform the test, a technician first stops the blood flow by wrapping the upper arm with an elastic band. He sterilizes the injection site with alcohol, inserts a needle into a vein in the arm, and draws the blood into a syringe. Once the technician draws enough blood, he undoes the band and withdraws the needle while pressing a cotton ball against the injection site. He then puts a bandage over the site and sends the blood to a lab for analysis.

Although the BUN test is often a safe procedure, it may result in phlebitis, which is the inflammation of the vein following a blood sample draw, warns WebMD. Drawing a blood sample from people with clotting disorders may also be problematic as it may result in prolonged bleeding. The needle can also cause bruises during the injection.