At a glance

Also known as

Blood urea nitrogen; BUN

Why get tested?

To evaluate kidney function and monitor the effectiveness of dialysis

When to get tested?

If you have non-specific symptoms that may indicate a kidney problem

Sample required?

A blood sample drawn from a vein in the arm

What is being tested?

Urea is produced when protein is broken down by the body. Healthy kidneys eliminate more than 90% of the urea the body produces, so blood levels indicate how well your kidneys are working.

How is the sample collected for testing?

A blood sample is drawn from a vein in the arm.

Is any test preparation needed to ensure the quality of the sample?

No test preparation is needed.

The Test

How is it used?

Urea and creatinine levels are used to evaluate kidney function and to monitor patients with kidney failure or those receiving dialysis.

When is it requested?

Urea may be used in a panel of tests:

  • when someone has non-specific illness,
  • as part of a routine testing panel, or
  • to check how the kidneys are functioning before starting to take certain drugs.

Urea is often ordered with creatinine:

  • if kidney problems are suspected,
  • to monitor treatment of kidney disease, or
  • to monitor kidney function while someone is on certain drugs.

What does the test result mean?

High urea levels suggest impaired kidney function. This may be due to acute or chronic kidney disease. However, there are many things besides kidney disease that can affect urea levels such as decreased blood flow to the kidneys as in congestive heart failure, shock, stress, recent heart attack or severe burns; bleeding from the gastrointestinal tract; conditions that cause obstruction of urine flow; or dehydration.

Low urea levels are not common and are not usually a cause for concern. They can be seen in severe liver disease or malnutrition but are not used to diagnose or monitor these conditions. Low urea is also seen in normal pregnancy.

About Reference or “Normal” Ranges

Is there anything else I should know?

Urea levels increase with age and also with the amount of protein in your diet. High-protein diets may cause abnormally high urea levels. Very low-protein diets can cause abnormally low urea. Lower urea levels are also seen in infants and small children.

Drugs that impair kidney function may increase urea levels. Your urea and creatinine may be monitored if you are on certain drugs.

Common Questions

What other tests are used with urea to check how my kidneys are functioning?

Urea and creatinine are often the first tests that are used to check how well the kidneys are able to filter waste products from your blood. Your doctor may also request electrolyte tests such as sodium and potassium, or calcium to help understand how your kidneys are functioning.

How does urea change with age?

Urea levels increase with age. Urea levels in very young babies are about 2/3 of the levels found in healthy young adults, while levels in adults over 60 years of age are slightly higher than younger adults. Levels are also slightly higher in men than women.

What happens to urea in pregnancy?

Urea levels are normally slightly lower in pregnancy, especially in the last few months when the fetus is using large amounts of protein for growth.

Last Review Date: June 6, 2013