Also Known As
BUN (Blood Urea Nitrogen) Test
This article was last reviewed on
This article waslast modified on 13 May 2022.
At a Glance
Why Get Tested?

To evaluate kidney function or to monitor the effectiveness of dialysis

When To Get Tested?

Urea is routinely measured as part of a “urea and electrolytes” (U&E) screen to assess kidney function. It may also be tested if you have symptoms of acute or chronic kidney disease.

Sample Required?

A blood sample taken from a vein in the arm

Test Preparation Needed?

No test preparation is needed

On average it takes 7 working days for the blood test results to come back from the hospital, depending on the exact tests requested. Some specialist test results may take longer, if samples have to be sent to a reference (specialist) laboratory. The X-ray & scan results may take longer. If you are registered to use the online services of your local practice, you may be able to access your results online. Your GP practice will be able to provide specific details.

If the doctor wants to see you about the result(s), you will be offered an appointment. If you are concerned about your test results, you will need to arrange an appointment with your doctor so that all relevant information including age, ethnicity, health history, signs and symptoms, laboratory and other procedures (radiology, endoscopy, etc.), can be considered.

Lab Tests Online-UK is an educational website designed to provide patients and carers with information on laboratory tests used in medical care. We are not a laboratory and are unable to comment on an individual's health and treatment.

Reference ranges are dependent on many factors, including patient age, sex, sample population, and test method, and numeric test results can have different meanings in different laboratories.

For these reasons, you will not find reference ranges for the majority of tests described on this web site. The lab report containing your test results should include the relevant reference range for your test(s). Please consult your doctor or the laboratory that performed the test(s) to obtain the reference range if you do not have the lab report.

For more information on reference ranges, please read Reference Ranges and What They Mean.

What is being tested?

Urea is the final breakdown product of the amino acids found in proteins. Nitrogen in the form of ammonia is produced in the liver when protein is broken down. The nitrogen combines with other chemicals in the liver to form the waste product urea. The urea is released into the bloodstream and carried to the kidneys where it is filtered out of the blood and excreted in the urine. Healthy kidneys remove more than 90% of the urea the body produces, so blood levels can show how well your kidneys are working.

Most diseases that affect the kidneys or liver can affect the amount of urea present in the blood. If increased amounts of urea are produced by the liver or decreased amounts are removed by the kidneys then blood urea concentrations will rise. If significant liver damage or disease reduces the production of urea then urea concentrations may fall.

Accordion Title
Common Questions
  • How is it used?

    Urea and creatinine levels are used to evaluate how well the kidney is working and to monitor patients with kidneys that are diseased or those receiving kidney dialysis.

  • When is it requested?

    Urea may alsonbe used in a panel of tests:

    • when someone has non-specific illness,
    • as part of a routine group of tests (often called “urea and electrolytes” (U&E),
    • to check how the kidneys are functioning before starting to take certain drugs.

    Urea is often requested with creatinine:

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

    Some symptoms and signs of kidney dysfunction include:

    • Tiredness, lack of concentration, poor appetite, poor sleep
    • Swelling or puffiness (oedema) around the eyes, wrists, ankles or tummy
    • Urine that is foamy, blood strained or coffee-coloured
    • A decrease in the amount of urine
    • Problems urinating such as a burning sensation, abnormal discharge during urination or a change in the frequency of urination especially at night
    • Mid-back pain below the ribs where the kidneys are located
    • High blood pressure
  • What does the test result mean?

    High urea levels suggest poor 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 levels are also seen in normal pregnancy.

  • 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 levels. Lower urea levels are also seen in infants and small children.

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

  • 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. This is when the foetus is using large amounts of protein for growth and the blood volume of the mother increases, causing dilution of the urea in the blood.