Kt/V Calculator Daugirdas

Calculate single-pool Kt/V with the Daugirdas second-generation formula, plus Urea Reduction Ratio and equilibrated Kt/V, to check hemodialysis dose adequacy against KDOQI targets.

Quick Facts

Adequacy target
spKt/V of 1.2 or higher per session
KDOQI minimum for thrice-weekly hemodialysis; many programs target 1.4 to allow for variability.
Formula
Daugirdas second-generation (1993)
-ln(R - 0.008t) + (4 - 3.5R) x UF/W, the most widely used clinical Kt/V equation.

Your Results

Calculated
Single-pool Kt/V
-
Daugirdas II formula
Urea Reduction Ratio
-
Percent BUN removed
Equilibrated Kt/V
-
Rate-corrected for rebound
Adequacy status
-
vs KDOQI targets

Ready

Enter pre- and post-dialysis BUN, session length, ultrafiltration volume, and weight, then calculate.

About the Kt/V Calculator (Daugirdas formula)

Kt/V is the standard measure of hemodialysis dose. K is the dialyzer's urea clearance, t is the treatment time, and V is the patient's urea distribution volume - so Kt/V is, in essence, the fraction of body water cleared of urea during one treatment. Rather than measuring K and V directly, clinicians use the Daugirdas second-generation formula to estimate Kt/V from blood urea nitrogen (BUN) drawn before and after dialysis, plus session length, fluid removed, and body weight.

The Daugirdas second-generation formula

The single-pool Kt/V (spKt/V) is calculated as:

spKt/V = -ln(R - 0.008 x t) + (4 - 3.5 x R) x UF/W

  • R is the ratio of post-dialysis BUN to pre-dialysis BUN.
  • t is the dialysis session length in hours.
  • UF is the ultrafiltration (fluid removal) volume in liters.
  • W is the patient's post-dialysis weight in kilograms.

This calculator also reports the Urea Reduction Ratio (URR = (1 - R) x 100%), a simpler adequacy measure, and an equilibrated Kt/V (eKt/V) that applies Daugirdas's rate-equation correction for post-dialysis urea rebound, using a slightly different correction for arteriovenous access versus a central venous catheter.

Interpreting the result

KDOQI (Kidney Disease Outcomes Quality Initiative) guidelines set a minimum single-pool Kt/V of 1.2 per session for patients dialyzing three times weekly, with a commonly cited delivered-dose target of 1.4 to build in a margin for treatment variability. Because equilibrated Kt/V corrects for urea rebound after the session ends, it runs somewhat lower than spKt/V for the same treatment - that difference is expected, not an error.

When to consult a professional

This tool performs the standard Kt/V arithmetic for education and record-keeping. It does not set or adjust a dialysis prescription. Any change to treatment time, blood flow, dialyzer, or frequency should be made with a nephrologist or dialysis care team, who can weigh residual kidney function, nutritional status, and other clinical factors alongside the number.

Frequently Asked Questions

What does the Kt/V calculator measure?
Kt/V is a measure of hemodialysis dose: K is the dialyzer urea clearance, t is treatment time, and V is the patient's urea distribution volume. This calculator uses the Daugirdas second-generation formula to estimate single-pool Kt/V (spKt/V) directly from pre- and post-dialysis BUN, session length, ultrafiltration volume, and post-dialysis weight, without measuring K or V separately.
How is Kt/V calculated with the Daugirdas formula?
The Daugirdas second-generation equation is spKt/V = -ln(R - 0.008 x t) + (4 - 3.5 x R) x UF/W, where R is the ratio of post-dialysis to pre-dialysis BUN, t is session length in hours, UF is ultrafiltration volume in liters, and W is post-dialysis weight in kilograms. The calculator also reports the Urea Reduction Ratio (URR) and an equilibrated Kt/V (eKt/V) that corrects for post-dialysis urea rebound.
What Kt/V value indicates adequate dialysis?
KDOQI clinical practice guidelines set a minimum single-pool Kt/V of 1.2 per hemodialysis session for patients treated three times weekly, with many programs targeting 1.4 or higher to allow for treatment variability. These are population-based targets - a nephrologist or dialysis care team should confirm what is appropriate for an individual prescription.

Related calculators