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Alternate Names

  • blood urea nitrogen


This test determines the level of urea nitrogen in the blood.

Who is a candidate for the test?

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.

How is the test performed?

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 After the needle is withdrawn; the puncture site is covered for a short time to prevent bleeding.

What is involved in preparation for the test?

A person should request specific instructions from his or her healthcare professional. Usually no preparation is necessary

What do the test results mean?

Normal values for BUN are 7 to 20 milligrams per deciliter (mg/dl) of blood. Levels lower than normal may indicate:
  • liver failure
  • a diet too low in protein
  • malnutrition
Levels higher than normal may indicate:
  • heart failure
  • gastrointestinal bleeding
  • burns
  • dehydration, or not having enough fluids and/or salts in the body
  • kidney disease or failure
  • shock
  • obstruction of the urinary tract
  • the effect of certain medications such as nonsteroidal anti-inflammatory drugs (NSAIDs), steroids such as prednisone, angiotensin-converting enzyme (ACE) inhibitors, and rarely tetracycline.

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