Diseases & Conditions

Blood Urea Nitrogen - BUN


Overview & Description

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

Urea nitrogen is produced when proteins are metabolized or broken down. Elevated levels of blood urea nitrogen (BUN) can be a sign of kidney disease, liver disease or dehydration.

Who is a candidate for the test?

This test is normally done to evaluate kidney function and aid in diagnosing kidney disease. It may also be performed to assess for dehydration.

How is the test performed?

In order to measure the BUN, or blood urea nitrogen, levels in the blood, 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 After the needle is withdrawn; the puncture site is covered for a short time to prevent bleeding.


Preparation & Expectations

What is involved in preparation for the test?

A person should request specific instructions from his or her healthcare provider.


Results and Values

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
  • overhydration, or too much fluid in the body
  • Levels higher than normal may indicate:

  • congestive heart failure, or heart disease
  • starvation
  • eating too much protein
  • gastrointestinal bleeding
  • burns
  • dehydration, or not having enough fluids in the body
  • myocardial infarction, or heart attack
  • kidney disease
  • kidney failure
  • shock
  • obstruction of the urinary tract

  • Attribution

    Author:David T. Moran, MD
    Date Written:
    Editor:
    Edit Date:
    Reviewer:H. William Kelly, PharmD
    Date Reviewed:04/17/01