URR (Urea Reduction Ratio) is one way to find out how much cleaner your blood is after dialysis. This is known as dialysis adequacy. A blood test that measures the blood urea nitrogen (BUN) is done at the beginning and at the end of your hemodialysis treatment.
The amount of urea in these two blood samples is compared to see how much was removed during dialysis. Although urea is just one of the body’s waste products, how effectively it is removed indicates how well other waste products have been removed. So, if you have a URR of 65%, it means your blood is 65% cleaner than when you started this dialysis treatment.