Urea and creatinine are waste products produced during protein metabolism. Both of these waste products are carried to the kidney and filtered into the urine. They are measured to evaluate how well the kidney is working. In the United States, urea is called "B.U.N.", or, Blood Urea Nitrogen. Although the correct name in the Canadian unit of measure is urea, you may still hear people use the term B.U.N. An elevated urea and creatinine indicates the kidneys are not working (called renal failure).

Although urea is filtered into the urine by the kidney, some of the filtered urea will get reabsorbed and reused by the body. Consequently, urea levels in the bloodstream can rise if the kidney fails, if the patient is making a lot of new protein (anabolic) or breaking a lot of protein down (catabolic) or if the patient is dehydrated.

Creatinine is a byproduct of muscle protein metabolism. Virtually all of the creatinine that we make is filtered by the kidney and eliminated in the urine. Creatinine is a more specific test of kidney function. While a rise in the creatinine usually indicates renal failure, massive muscle damage can also cause the creatinine level to rise.


Image 1: Urea and Creatinine are used to evaluate how well the kidney is working.





Last Reviewed: October 23, 2014