A blood urea nitrogen test, often called a BUN test, is used to determine if the kidneys and liver are working properly. The test looks at the level of nitrogen in the blood. Nitrogen is produced by urea, a type of chemical waste made from proteins broken down in the liver. An individual with elevated blood urea nitrogen levels may have kidney malfunction, while lower levels may indicate a liver abnormality.
The kidneys are responsible for filtering urea from the body. In general, this chemical leaves the liver and enters the kidneys, where it is expelled from the body during urination. Properly functioning kidneys will filter it effectively, but when there is a problem with the organs, urea builds up in the bloodstream. A blood urea nitrogen test will reflect an increase in excess urea nitrogen.
In most cases, the blood test is done if a medical professional suspects an abnormality in the kidneys. The patient may have symptoms such as frequent urination, flank pain, decreased urination, or lower back pain. For people with kidney disease, the test may be done to detect the extent of kidney damage or to see how well an established treatment is working. For example, individuals on dialysis may receive frequent blood tests to assess the effectiveness of their treatments.
Commonly, blood creatinine levels can also be obtained during a blood urea nitrogen test. Creatinine, like urea, is a waste product that is normally filtered out by healthy kidneys. For this reason, the presence of creatinine in the blood can also indicate a kidney problem. When a urea nitrogen and creatinine test are done at the same time, the results will usually be compared for a BUN-to-creatinine ratio.
A blood sample is needed for the test, which is generally considered painless, except for a minor needle prick. As with any injection site, there is a minimal risk of infection, although this does not happen often. After the blood is drawn, there may be some minor bruising. In the event that the injection site begins to bleed rapidly, an individual should apply pressure to the site and seek immediate medical attention.
Patients are generally informed of the results of a blood urea nitrogen test as soon as the results are received by the ordering health care professional. High blood urea nitrogen levels can indicate a problem with the kidneys, from an infection to abnormal growth or disease. There may be a problem with the liver if a test reveals particularly low levels. Medical providers will usually treat the condition causing the abnormal levels, although there are benign conditions that can cause blood urea nitrogen levels to become unbalanced in either direction.