This test determines the level of urea nitrogen in the blood.
At one time, this test was normally done to evaluate kidney function and aid in diagnosing kidney disease. Since an elevated BUN has numerous other causes unrelated to kidney disease, it is relied on less frequently today. It may also be performed to assess for dehydration.
In order to measure the BUN, a blood sample is taken from a vein on the forearm or hand. First, the skin over the vein is cleaned with an antiseptic. Next, a strong rubber tube, or "tourniquet", is wrapped around the upper arm to enlarge the veins in the lower arm by restricting blood flow through them.
A fine needle is gently inserted into a vein, and the tourniquet is removed. Blood flows from the vein through the needle, and is collected in a syringe or vial for testing in the laboratory. After the needle is withdrawn; the puncture site is covered for a short time to prevent bleeding.
A person should request specific instructions from his or her healthcare professional. Usually no preparation is necessary
Normal values for BUN are 7 to 20 milligrams per deciliter (mg/dl) of blood. Levels lower than normal may indicate: liver failurea diet too low in proteinmalnutrition
Levels higher than normal may indicate: heart failuregastrointestinal bleedingburnsdehydration, or not having enough fluids and/or salts in the bodykidney disease or failureshock obstruction of the urinary tractthe effect of certain medications such as nonsteroidal anti-inflammatory drugs (NSAIDs), steroids such as prednisone, angiotensin-converting enzyme (ACE) inhibitors, and rarely tetracycline.