Blood Urea Nitrogen
What is BUN?
Blood urea nitrogen test is also known as urea nitrogen test or BUN. This test is done to evaluate the overall health of the kidney, to diagnose kidney diseases, and to monitor the treatment of kidney diseases such as dialysis.
Why is BUN done?
The Blood Urea Nitrogen test is done:
As a part of the routine comprehensive check-up
As a part of the basic metabolic panel
In case of signs and symptoms of kidney disease
In case a patient is undergoing treatment for kidney disease
What does BUN Measure?
The Blood Urea Nitrogen test measures the amount of urea nitrogen in the blood. Urea is a waste product which is formed in the liver. It is formed when protein is metabolized into amino acids. This leads to the production of ammonia which is further converted into urea which is a less toxic waste product.
Both ammonia and urea have nitrogen as their component. The liver releases urea into the blood which is then carried out to the kidneys. Here, it is filtered out of the blood and then released into the urine. Since this is a continuous process, a small and stable amount of urea nitrogen always remains in the blood.
In the case of kidney or liver diseases, there is a change in the amount of urea present in the blood. If the liver produces urea in increased amounts or if there is any problem in the functioning of the kidneys, there can be difficulty in filtering out wastes of the blood which will lead to rising in urea concentrations in the blood. If due to liver damage or disease there is less production of urea, the concentration of BUN will fall.
The BUN test is done along with creatinine test to evaluate kidney function to diagnose kidney disease and to monitor patients undergoing treatment of kidney disease.
Interpreting BUN results
The reference range for BUN is as follows:
Reference range in mg/dL
0 - 1 week
3 - 25
1 week - 1 year
1 - 12 years
5 - 18
12 - 60 years
6 - 20
60 - 90 years
> 90 years
10 - 31
Reference range may vary from lab to lab*