Blood Urea Level Test - Blood Urea Test

This test measures the concentration of blood urea nitrogen (BUN), or urea, in the serum. Urea is the main end product of protein metabolism in the liver, where it is formed from toxic ammonia. Urea is filtered from the blood by the kidneys and excreted in the urine. The level of urea in the blood reflects the interaction of three factors: the rate of protein production by the liver, the filtration function of the kidneys, and the rate of urine flow. Therefore, it rises when kidney function is impaired, but it can also rise for reasons not directly related to the kidneys.