Dialysis: Measuring How Well It Works

Topic Overview

Dialysis removes urea and other waste products from the blood. To find out how well dialysis is working, you will have blood tests that look at the level of urea in your blood. Usually these tests are done once a month, at the beginning of your session and again at the end. Two measures show how well dialysis is working: urea reduction ratio (URR) and Kt/V.

Urea reduction ratio

One way to measure how well hemodialysis is removing urea from the body is to measure blood urea nitrogen (BUN) level. The BUN is measured before and after your treatment session. Then the two numbers are compared to see how much the urea level in the blood has decreased. This difference is called the urea reduction ratio (URR), and it is usually expressed as a percentage. An adequate dose of hemodialysis should result in an average URR of 65%.

Kt/V

Another way to measure the effectiveness of hemodialysis is to compare the amount of fluid that is cleared of urea during each dialysis session with the amount of fluid that exists in the body. This is called the Kt/V.

• Kt represents the amount of fluid that is cleared of urea during each dialysis session. It is measured in milliliters per minute (mL/min).
• V represents the volume of water a person's body contains.

The Kt/V is the most accurate measure of hemodialysis, because it also measures the amount of urea removed with excess fluid and takes into consideration other factors, such as weight loss during dialysis. An adequate dose of hemodialysis should result in an average Kt/V of 1.2.

What to think about

An adequate dose of dialysis can usually be delivered in 3 to 5 hours.