Also known as: Urea nitrogen, Urea
Name: Blood urea nitrogen
Related tests: Creatinine, CMP, BMP
Why is the test done?
To assess kidney function and monitor the effect of dialysis and other treatments related to kidney disease or damage.
When is it done?
As part of routine testing or a basic metabolic panel, and when you are acutely or chronically ill with a condition that could cause or be made worse by kidney dysfunction.
What samples are required?
A blood sample taken from a vein in the arm.
What is being analysed?
The 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 down into its individual components (amino acids) and metabolised. The nitrogen combines with other molecules in the liver to form the waste product urea. Urea is then released into the bloodstream and carried to the kidneys, where it is filtered and excreted in the urine. Because this is a continuous process, there is usually a small but stable amount of urea nitrogen in the blood. Many diseases and conditions affecting the kidneys or liver can influence the amount of urea in the blood. If the amount of urea produced by the liver increases, or the amount excreted by the kidneys decreases, the urea concentration will rise. If liver damage or disease inhibits urea production, the BUN concentration may fall.
How is it used?
When is it requested?
What does the test result mean?
Is there anything else I should know?
How is it used?
The BUN test is mainly used, together with the creatinine test, to assess kidney function in a wide variety of conditions and to monitor patients with chronic kidney dysfunction or heart attacks. It can be used to assess a person’s general state of health when requested as part of a basic metabolic panel (BMP) or comprehensive metabolic panel (CMP).
When is it requested?
BUN is part of both the BMP and the CMP, groups of tests usually used:
• when a person has no specific illness
• as part of a routine panel of tests
• to assess kidney function before starting drug treatment
• when an acutely ill person arrives at A&E and/or is admitted to hospital
• during a hospital stay, BUN is often requested together with creatinine
• when kidney problems are suspected
• at regular intervals to monitor kidney function in patients with chronic diseases such as diabetes,
congestive heart failure and heart attacks
• at regular intervals to monitor kidney function and treatment in patients with kidney disease
• before and during certain drug treatments to monitor kidney function, or
• at regular intervals to monitor the effectiveness of dialysis
What does the test result mean?
Raised BUN levels suggest impaired kidney function. This may be due to acute or chronic kidney disease, damage or failure. It may also be due to a condition that reduces the blood supply to the kidneys, such as congestive heart failure, shock, stress, a recent heart attack or severe burns, to conditions that block the flow of urine, or to dehydration. BUN may be raised when there is excessive protein breakdown (catabolism), a significant increase in dietary protein, or bleeding in the gut (because of the proteins in the blood).
Low BUN levels are not common and are not usually a cause for concern. They may be seen in severe liver disease, malnutrition and sometimes when a patient is overhydrated (too much fluid volume), but the BUN test is not usually used to diagnose or monitor these conditions.
Both increases and decreases in BUN can be seen during normal pregnancy.
If one kidney is working perfectly, BUN concentrations may be normal even when there is significant dysfunction in the other kidney.
Is there anything else I should know?
BUN levels can rise with the amount of protein in the diet. High-protein diets can cause abnormally high BUN, while low-protein diets can cause abnormally low BUN.