What is the acceptable range for Urea Reduction Ratio (URR) in dialysis?

From the Guidelines

The acceptable range for URR in dialysis is at least 70%, as it corresponds to a Kt/V of 1.3, which is the recommended minimum dose of hemodialysis. This recommendation is based on the study by 1, which suggests that a Kt/V of 1.3 is necessary to prevent the delivered dose of hemodialysis from falling below the recommended minimum dose.

Key Considerations

• The URR corresponding to a Kt/V of 1.3 can vary substantially as a function of ultrafiltration, highlighting the importance of considering individual patient factors when determining the acceptable URR range.
• Factors such as compromised urea clearance, reductions in treatment time, and errors in prescribed blood and dialysate flow rates can result in the actual delivered dose of hemodialysis falling below the prescribed dose, emphasizing the need for careful monitoring and adjustment of dialysis parameters.
• Achieving a URR of at least 70% is crucial for ensuring proper removal of uremic toxins, better control of electrolytes, and improved patient outcomes, as inadequate dialysis (URR below 65%) is associated with increased morbidity and mortality.

Clinical Implications

• Nephrologists should prescribe doses of hemodialysis that are higher than the minimum delivered levels to account for potential factors that may compromise the delivered dose.
• Regular monitoring of URR and Kt/V is necessary to ensure that patients receive the minimum adequate dose of hemodialysis at all treatments.
• Clinicians should aim to optimize dialysis parameters, including blood and dialysate flow rates, treatment time, and ultrafiltration, to achieve the target URR range and improve patient outcomes.

From the Research

Urea Reduction Ratio (URR) Acceptable Range in Dialysis

• The URR is a measure of the fractional reduction of blood urea concentration during a single hemodialysis treatment 2.
• A minimum URR value of 65% was previously recommended to optimize survival 2.
• However, studies have shown that the median URR and the URR threshold for mortality benefit have increased over time, suggesting that a higher URR may be necessary for optimal outcomes 2.
• The threshold URR values were found to be 61.1,65.0,68.0, and 71.0% for 1994 through 1997 in models adjusted for case mix 2.
• Another study found that patients with a URR less than 65% had a higher body weight and were more likely to be male, have a shorter dialysis duration, and have lower serum albumin levels 3.
• A more recent study suggested that targeting a URR ≥0.67 provides a simplified means of assessing adequacy of intermittent hemodialysis in patients with acute kidney injury 4.
• The acceptable range for URR may vary depending on the patient population and the specific dialysis treatment, but a general range of 65-75% is commonly cited 2, 3, 4.

Factors Affecting URR

• Patient-specific demographic variables, such as body weight, gender, and age, can affect URR 3.
• Treatment-specific parameters, such as dialyzer membrane type and dialysis session length, can also impact URR 3.
• The use of urea-selective membranes may improve the efficiency of urea removal and increase the acceptable range for URR 5.

Clinical Implications

• The URR is an important measure of dialysis adequacy and can be used to assess the delivered dose of hemodialysis 2, 4.
• Clinicians should consider the acceptable range for URR when evaluating the effectiveness of dialysis treatment and making adjustments to the treatment protocol 2, 3, 4.