BUN, Blood Urea Nitrogen

This is a blood test to check kidney function. It also helps to monitor the effectiveness of dialysis and other treatments related to kidney disease or damage.

This test measures the amount of urea nitrogen in the blood. Nitrogen, in the form of ammonia, is produced in the liver when protein is broken into its component parts (amino acids) and metabolized. The nitrogen combines with other molecules in the liver to form the waste product urea. The urea is then released into the bloodstream and carried to the kidneys, where it is filtered out of the blood and excreted in the urine. Since this is an ongoing process, there is usually a small but stable amount of urea nitrogen in the blood.

Most diseases or conditions that affect the kidneys or liver have the potential to affect the amount of urea present in the blood. If increased amounts of urea are produced by the liver or decreased amounts are excreted by the kidneys, then urea concentrations will rise. If significant liver damage or disease inhibits the production of urea, then BUN concentrations may fall.

The BUN test is primarily used, along with the creatinine test, to evaluate kidney function under a wide range of circumstances and to monitor patients with acute or chronic kidney dysfunction or failure. It also may be used to evaluate a person's general health status when ordered as part of a basic metabolic panel (BMP) or comprehensive metabolic panel (CMP).


A blood sample is obtained by inserting a needle into a vein in the arm.


  • Adult: 10-20 mg/dL or 3.6-7.1 mmol/L (SI units)

  • Elderly: may be slightly higher than adult.

  • Child: 5-18 mg/dL

  • Infant: 5-18 mg/dL

  • Newborn: 3-12 mg/dL

  • Cord: 21-40 mg/dL

Ranges for normal findings may vary among different laboratories and hospitals. You should always check with your doctor after having lab work or other tests done to discuss the meaning of your test results and whether your values are considered within normal limits.


Your caregiver will go over the test results with you and discuss the importance and meaning of your results, as well as treatment options and the need for additional tests if necessary.


It is your responsibility to obtain your test results. Ask the lab or department performing the test when and how you will get your results.