Blood Urea Nitrogen: Normal Range

Urea is a waste product formed in the liver when protein is metabolized into its component parts. The test of Blood Urea Nitrogen (BUN) measures the amount of urea nitrogen in the blood.

Why to Get Tested

The purposes of BUN test are to:

  • help diagnose kidney disease;
  • evaluate the health of your kidneys;
  • monitor the effectiveness of dialysis and other treatments related to kidney disease or damage.

Normal Range

Occasionally, a health practitioner will look at the ratio between a person’s BUN and blood creatinine to help determine what is causing BUN concentrations to be higher than normal.

The normal ratio of BUN to creatinine is usually between 10:1 and 20:1.

An increased ratio may be due to:

  • acute or chronic kidney disease, damage, or failure
  • a condition, such as congestive heart failure, shock, stress, recent heart attack, or severe burns, which causes a decrease in the flow of blood to the kidneys
  • conditions that cause obstruction of urine flow
  • dehydration
  • increased protein in the diet
  • gastrointestinal bleeding (because of the proteins present in the blood).

Low BUN levels are not common and are not usually a cause for concern. The ratio may decrease with:

  • liver disease (due to decrease in the formation of urea)
  • malnutrition.

However, the BUN test is not usually used to diagnose or monitor these conditions.


Keywords: Blood Urea Nitrogen; BUN

* The Content is not intended to be a substitute for professional medical advice, diagnosis, or treatment. Always seek the advice of your physician or other qualified health provider with any questions you may have regarding a medical condition.