Urea Reduction Ratio (URR) is a number that tells you how well hemodialysis is removing waste products from your body, that is, how effective your dialysis treatments are.

The URR is a percentage based on how much urea was removed during your treatment on the day your blood was drawn. This is calculated by testing the urea level in your blood (blood urea nitrogen, or BUN) before and after the dialysis treatment.

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. Many doctors use URR to monitor your dialysis treatments. As part of your own treatment team, you should know your monthly URR and ask questions when it gets too low.