Kt/V Calculator
Calculate dialysis adequacy with Daugirdas Kt/V and URR from pre and post-dialysis BUN, ultrafiltrate, and weight.
What Is Kt/V?
Kt/V is the standard measure of dialysis adequacy — how effectively hemodialysis or peritoneal dialysis removes urea from the blood. The Daugirdas formula combines pre- and post-dialysis blood urea nitrogen (BUN) with ultrafiltrate volume and patient weight to estimate single-pool Kt/V. Related tools include the Kidney Failure Risk Calculator.
How Kt/V Is Calculated
Urea reduction ratio (URR) is calculated as (pre BUN − post BUN) / pre BUN × 100. The Daugirdas Kt/V equation is: Kt/V = −ln(post/pre − 0.03) + (4 − 3.5 × post/pre) × (UF / weight), where UF is ultrafiltrate in liters and weight is post-dialysis weight in kilograms. BUN values are in mg/dL.
Interpreting Kt/V Results
For hemodialysis, a single-session Kt/V of at least 1.2 indicates adequate dialysis. For peritoneal dialysis, a weekly Kt/V of at least 1.7 is the usual adequacy target. Values below these thresholds suggest the prescription may need review. URR above 65% often correlates with adequate hemodialysis but Kt/V is the preferred metric.
Frequently Asked Questions
What is a good Kt/V for hemodialysis?
A single hemodialysis session Kt/V of 1.2 or higher is considered adequate. Many centers aim for 1.4 or above for additional margin.
What Kt/V target applies to peritoneal dialysis?
Peritoneal dialysis adequacy is assessed weekly. A weekly Kt/V of at least 1.7 is the standard target for continuous ambulatory or automated peritoneal dialysis.
What is URR and how does it relate to Kt/V?
Urea reduction ratio (URR) is the percentage drop in BUN during dialysis. URR above 65% often indicates adequate hemodialysis, but Kt/V accounts for ultrafiltration and body size and is preferred for prescribing.
When should BUN samples be drawn?
Pre-dialysis BUN is drawn before the session starts. Post-dialysis BUN is drawn from the arterial line or venous port at session end, with slow flow and proper technique to avoid dilution error.
Why use the Daugirdas formula?
The second-generation Daugirdas equation adjusts for ultrafiltration and urea rebound, providing a more accurate single-pool Kt/V than URR alone. It is widely used in clinical practice and quality reporting.
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