Contributed by Healthians Team

What is blood urea nitrogen serum test?

A blood urea nitrogen (BUN) test is used to determine how well your kidneys are working. It measures the amount of urea nitrogen present in your blood. Urea nitrogen is a waste product created when your body breaks down protein. Normally, it is removed from the body after urination. BUN levels rise when your kidneys or liver are damaged. An excess of urea nitrogen in your blood may indicate kidney or liver complications.

Your liver produces ammonia, which contains nitrogen after breaking down protein for your cells. This nitrogen combines with other elements such as carbon, hydrogen and oxygen to form urea, a waste product. This urea travels through your bloodstream from your liver to your kidneys. Your healthy kidneys filter urea and remove waste from your blood that leaves your body through urine.

Who should get tested?

This test is commonly used to evaluate kidney function. It is often done along with other blood tests such as creatinine blood test for accurate diagnosis. Your doctor may need a blood urea nitrogen test if they suspect that you have kidney damage or need to evaluate your kidney function. If you receive hemodialysis or peritoneal dialysis, this helps determine the efficiency of the dialysis treatment. BUN is also tested as part of routine checkups or after treatment for conditions such as diabetes.

Why is testing necessary?

The BUN test is used as part of a group of blood tests that help diagnose other conditions such as liver damage, urinary tract obstruction, congestive heart failure, or gastrointestinal bleeding. If kidney problems are the main concern, your creatinine levels will be measured while urea nitrogen levels are checked. Creatinine is another waste product that healthy kidneys filter out of your body through urine. High levels of creatinine in your blood can indicate kidney damage. Your doctor can check how well your kidneys are removing waste from your blood.

What do test results mean?

Blood urea nitrogen test results are measured in milligrams per deciliter (mg/dL) in the United States and millimoles per liter (mmol/L) internationally. About 7 to 20 mg/dL (2.5 to 7.1 mmol/L) is considered normal. However, the normal range may vary depending on the reference range used by the lab and your age.

Urea nitrogen levels tend to increase as you age. Nitrogen levels in children are low and the range fluctuates between children. Generally, high blood urea nitrogen levels mean your kidneys are not working properly. However, your high blood urea nitrogen may be caused by a urinary tract obstruction, congestive heart failure, or a recent heart attack. In addition, you may experience an increase in blood urea nitrogen if you are suffering from gastrointestinal bleeding, dehydration, shock, severe burns, a high-protein diet, and certain medications such as antibiotics.

How is the test done?

During a blood urea nitrogen test, a lab technician inserts a needle into a vein in your arm and takes a blood sample. This blood sample is sent to a lab for analysis. The procedure does not require much time.

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