# URR Calculator - Urea Reduction Ratio

*The urea reduction ratio and serum albumin concentration as predictors of mortality in patients undergoing hemodialysis;*The New England journal of medicine; September 1993

The URR calculator allows you to check whether the performed dialysis was of good quality - **adequate to the patient's state** - using the **urea reduction ratio (URR)** calculations.

Follow the short text below to remind yourself about the most important issues connected to the URR **lab tests**, the use of URR in dialysis, and its basic formula.

We'll also refresh your knowledge on the **hemodialysis adequacy guidelines**. 🚰

*We try our best to make our Omni Calculators as precise and reliable as possible. However, this tool can never replace professional medical advice.*

## What does URR stand for, and how to use it?

The *URR* is an abbreviation for the **urea reduction ratio** - we can also call it the **urea reduction percentage (PRU)**. You should measure it every month or on every 12th dialysis session.

URR is a simple method for assessing the quality of dialysis (a life-saving treatment used in the final stage of kidney failure). It is **directly connected to the patient's outcome**. The URR assesses the ability of the dialysis to **eliminate the waste products from the blood**. Because of its simplicity, this ratio can also be used for various comparisons, within one patient's results or the entire nation's dialysis standards.

URR is also closely related to the **Kt/V equation**- both of these values can be used as **dialysis adequacy tests** (you can read more about Kt/V in the paragraph below, or in a separate Kt/V dialysis calculator).

❗ The dialysis is considered to be adequate, only if the **URR ratio is greater than or equal to 65% (≥65%).**

The studies have confirmed that patients with lower than adequate URR values had more health problems and a greater risk of death.

**What can we do to increase the URR?**

**Increase time on dialysis**;**Increase blood flow through the dialyzer**- it's the case of both the dialyzer and the quality of the patient's blood vessels;**Find and eliminate any circulation problems**.

**Interested in the topic?** Omni has plenty of useful tools to offer. For instance, you can use GFR calculator for detecting a kidney disease at its early stage and urine output calculator for computing fluid balance and urine output rate (ml/kg) per hour.

## How to calculate URR in dialysis?

The URR calculations for dialysis are straightforward, and **you can easily perform them single-handed!** In this section, we'd like to present two different versions of the urea reduction ratio formula - **choose the one that suits you best**.

💡 The choice of **urea units** is wide (mg/dL, mg%, mg/L, g/L, g/dL); you only need to remember to **use the same unit** for both urea values.

For example, if a patient's urea level before the dialysis is equal to **40 mg/dL**, and afterward is lower than **20 mg/dL**, we can perform the following URR calculations:

`URR = [(40 mg/dL - 20 mg/dL)/40 mg/dL] × 100%`

`URR = [20/40] × 100%`

`URR = ½ × 100% = 50%`

**Our URR is lower than 65%, which means that the performed dialysis was not adequate.**

**Still hungry for knowledge?** 🍰=📚

Check one of our brilliant, topic-related tools, such as FEUrea for Acute Kidney Injury (AKI) and BUN/ creatinine ratio for prerenal causes of AKI.

## URR versus Kt/V

URR can also be calculated using the **Kt/V equation for dialysis**; we can put the relationship between these two values into the following equation:

`(K × t)/V = -ln(1 - URR)`

where:

`K`

means the dialyzer clearance; describes the blood flow rate in**milliliters per minute**(mL/min);`t`

is the time of dialysis in**minutes**;`V`

stands for total body fluid volume;`URR`

is the short version of Urea Reduction Ratio, given in**%**; and`ln`

is used in mathematics to indicate the use of natural logarithm.

## FAQ

### How do I know if my URR value is normal?

The URR value is normal if it is **greater than or equal to 65%**. If you want to know if your URR value is normal, you will need to calculate it, using:

- The pre-dialysis urea level and the post-dialysis urea level; or
- The Kt/V value.

### What does a URR value of 55% mean in hemodialysis therapy?

A URR value of 55% in hemodialysis therapy may indicate that the treatment may not reach the desired effectiveness level. The dialysis is considered adequate only if the **URR ratio is greater than or equal to 65% (≥65%).**

### How do I calculate URR from Kt/V?

To calculate the URR from the value of Kt/V, you can use the following equation:

`(K × t)/V = -ln(1 - URR)`

Where,

`K`

is the dialyzer clearance;`t`

is the time of dialysis in**minutes**; and`V`

is the total body fluid volume.

Of course, it is easier if you use Omni's URR Calculator.

### What is the pre-dialysis urea level if the URR is 70%?

**50 mg/dL**. To calculate it, you will need to know the following:

**The post-dialysis urea level**. Let’s assume that the post-dialysis is`15mg/dL`

.- The URR. In our case, we will assume it is
`70%`

. - That’s it. If you apply these values in the equation
**URR=[(Upre−Upost)/Upre]⋅100%**, you will find that the pre-dialysis urea level is**50 mg/dL**. You can verify it using our calculator!

**Kt/V vs. URR relationship**, try the Kt/V calculator.