Enter the BUN level measured before the dialysis session (mg/dL or mmol/L).
Enter the BUN level measured immediately after the dialysis session.
Calculated Urea Reduction Rate:
0%
function calculateURR() {
// Get input values
var preVal = document.getElementById('preBUN').value;
var postVal = document.getElementById('postBUN').value;
// Convert to floats
var pre = parseFloat(preVal);
var post = parseFloat(postVal);
var resultBox = document.getElementById('resultBox');
var resultDisplay = document.getElementById('urrResult');
var statusDisplay = document.getElementById('urrStatus');
// Validation
if (isNaN(pre) || isNaN(post)) {
alert("Please enter valid numerical values for both Pre and Post BUN levels.");
return;
}
if (pre <= 0) {
alert("Pre-dialysis BUN must be greater than zero.");
return;
}
if (post = pre) {
alert("Post-dialysis BUN should typically be lower than Pre-dialysis BUN for a valid reduction rate calculation.");
// We allow calculation but warn, as strictly mathematical it's possible but clinically indicates an issue.
}
// Calculation: URR = ( (Pre – Post) / Pre ) * 100
var urr = ((pre – post) / pre) * 100;
// Round to 1 decimal place
var urrRounded = urr.toFixed(1);
// Display Results
resultBox.style.display = 'block';
resultDisplay.innerHTML = urrRounded + '%';
// Interpretation based on KDOQI Guidelines
// Target is usually >= 65%
if (urr >= 65) {
statusDisplay.innerHTML = "Status: Adequate Dialysis.Your URR meets the general KDOQI target of 65% or higher.";
statusDisplay.className = "result-interpretation status-adequate";
} else {
statusDisplay.innerHTML = "Status: Inadequate Dialysis.Your URR is below the recommended target of 65%. Please consult your healthcare provider.";
statusDisplay.className = "result-interpretation status-inadequate";
}
}
Understanding the Urea Reduction Rate (URR)
The Urea Reduction Rate (URR) is a critical metric used in nephrology to assess the adequacy of hemodialysis treatment. It measures the percentage of urea removed from a patient's blood during a single dialysis session. Since urea is a waste product generated by normal protein metabolism, its removal is a primary surrogate marker for the removal of other uremic toxins.
Ensuring an adequate URR is vital for reducing mortality and morbidity in End-Stage Renal Disease (ESRD) patients. Regular monitoring helps clinical teams adjust dialysis prescriptions to ensure patients receive sufficient therapy.
Key Takeaway: The National Kidney Foundation's KDOQI guidelines generally recommend a URR of 65% or higher to ensure dialysis adequacy.
How is URR Calculated?
The calculation for URR is straightforward and relies on two primary blood tests taken during the dialysis session: the pre-dialysis BUN and the post-dialysis BUN.
Consider a patient with the following lab results:
Pre-dialysis BUN: 60 mg/dL
Post-dialysis BUN: 18 mg/dL
Using the formula:
Subtract Post from Pre: 60 – 18 = 42
Divide by Pre: 42 / 60 = 0.70
Multiply by 100: 0.70 × 100 = 70%
In this example, the URR is 70%, which indicates adequate dialysis (as it is above the 65% threshold).
URR vs. Kt/V
While URR is commonly used due to its simplicity, another metric called Kt/V (Daugirdas formula) is often preferred by nephrologists for a more precise measure of dialysis dose. Kt/V takes into account factors that URR ignores, such as:
Ultrafiltration (fluid removal) during the session.
Urea generation during the session.
However, URR remains a valuable, quick estimation tool. A URR of 65% roughly correlates to a Kt/V of 1.2, which is the minimum recommended dose for hemodialysis.
Factors Affecting Urea Reduction Rate
If your URR calculation returns a value lower than expected, several factors might be responsible:
Access Recirculation: If the cleaned blood returns to the dialyzer immediately without circulating through the body, clearance is reduced.
Dialyzer Efficiency: The surface area and membrane type of the dialyzer affect how much urea is removed.
Treatment Time: Reducing dialysis time significantly lowers URR.
Sampling Errors: Drawing the post-dialysis blood sample incorrectly (e.g., from the venous line without slowing the pump) can lead to falsely high or low results.
Clinical Guidelines
According to the Kidney Disease Outcomes Quality Initiative (KDOQI):
The minimum delivered dose of hemodialysis should be a Kt/V of 1.2.
This corresponds to a minimum URR of approximately 65%.
To ensure this minimum is met, target doses are often set higher (e.g., URR target of 70%) to account for variations in treatment delivery.
Disclaimer: This calculator is for educational purposes only and should not replace professional medical advice. Always consult with a nephrologist regarding dialysis prescriptions and lab results.