Urea is a waste product formed in the liver when protein is metabolized into its component parts (amino acids) . This process produces ammonia, which is then converted into the less toxic waste product urea. This test measures the amount of urea nitrogen in the blood. N is a component of both ammonia and urea. Urea and urea nitrogen are referred to somewhat interchangeably because urea contains nitrogen and because urea/urea nitrogen is the “transport method” used by the body to rid itself of excess nitrogen. Urea is released by the liver into the blood and is carried to the kidneys, where it is filtered out of the blood and released into the urine. Since this is an ongoing process, there is usually a small but stable amount of urea N in the blood. Most diseases or conditions that affect the kidneys or liver have the potential to affect the amount of urea present in the blood. If increased amounts of urea are produced by the liver or if the kidneys are not working properly and have difficulty filtering wastes out of the blood, then urea concentrations will rise in the blood. If significant liver damage or disease inhibits the production of urea, then BUN concentrations may fall.
How is the sample collected for testing?
A blood sample is drawn from a vein in the arm.
Is any test preparation needed to ensure the quality of the sample?
No test preparation is needed.