Kt/V Calculator — Haemodialysis Adequacy (Daugirdas)
Calculate the single-pool Kt/V (spKt/V) using the Daugirdas second-generation formula from pre- and post-dialysis BUN, session time, ultrafiltration volume and post-weight — the standard measure of haemodialysis adequacy.
mg/dL
mg/dL
hours
L
kg
Excellent (≥ 1.4)
- 1
BUN ratio R
18 ÷ 60 = 0.3R = post-dialysis BUN ÷ pre-dialysis BUN. Lower R means more urea was removed. - 2
Logarithmic clearance term
−ln(0.3 − 0.008 × 4) = 1.317 - 3
Ultrafiltration correction term
(4 − 3.5 × 0.3) × (2 ÷ 70) = 0.084 - 4
Single-pool Kt/V
1.317 + 0.084 = 1.40
How does this calculator work?
spKt/V = −ln(R − 0.008t) + (4 − 3.5R) × UF/W (Daugirdas 1993), where R = BUN_post/BUN_pre, t = hours, UF = litres removed, W = post-weight in kg. KDOQI minimum target is spKt/V ≥ 1.2 for thrice-weekly HD. Enter five lab and session values to check adequacy and see URR alongside.
Formula
How this is calculated
Kt/V is the gold-standard metric for haemodialysis dose. K is dialyser urea clearance (mL/min), t is session time (min), and V is the urea distribution volume (mL) — approximately equal to total body water. Together Kt/V represents how many volumes of distribution were cleared of urea during the session. The KDOQI 2015 guidelines require a minimum spKt/V of 1.2 per session for conventional thrice-weekly HD; many centres target ≥ 1.4 for a safety margin.
This calculator uses the Daugirdas second-generation single-pool formula (1993): spKt/V = −ln(R − 0.008 × t) + (4 − 3.5 × R) × UF/W, where R = BUN_post/BUN_pre, t is session duration in hours, UF is ultrafiltration volume in litres, and W is post-dialysis body weight in kg. The logarithmic term captures diffusive urea clearance; the second term corrects for convective removal and the concentration-diluting effect of fluid removal. Blood draws should be taken immediately before the session and within 5 minutes of ending it (before significant urea rebound).
Limitations: the single-pool model assumes urea distributes in one compartment. In practice a two-compartment equilibration rebound occurs 30–60 minutes after session end (the equilibrated eKt/V is ~0.2 units lower than spKt/V). This calculator computes spKt/V only and does not substitute for clinical judgement or formal adequacy assessment by a nephrologist.
Frequently asked questions
KDOQI 2015 guidelines require a single-pool spKt/V of at least 1.2 per session for thrice-weekly conventional haemodialysis. Values below 1.2 are associated with higher morbidity and mortality; most centres aim for ≥ 1.4 as a safety margin.
The single-pool spKt/V is calculated from blood draws immediately before and immediately after the session. The equilibrated eKt/V accounts for the post-session rebound of urea from intracellular compartments (measured 30–60 min after session end) and is typically about 0.2 units lower than spKt/V.
Both measure dialysis adequacy from urea removal. URR (= (BUN_pre − BUN_post)/BUN_pre × 100) is simpler but ignores ultrafiltration and session time. A URR of 65% corresponds approximately to an spKt/V of 1.2. Kt/V is preferred in formal adequacy reporting because it captures more of the clinical picture.
Also known as
TG we-Calculate Editorial Team. (2026). Kt/V Calculator — Haemodialysis Adequacy (Daugirdas) [Online calculator]. TG we-Calculate. https://we-calculate.com/calculator/kt-v-calculator
TG we-Calculate Editorial Team. "Kt/V Calculator — Haemodialysis Adequacy (Daugirdas)." TG we-Calculate. 2026. https://we-calculate.com/calculator/kt-v-calculator.
TG we-Calculate Editorial Team, "Kt/V Calculator — Haemodialysis Adequacy (Daugirdas)," TG we-Calculate, 2026. [Online]. Available: https://we-calculate.com/calculator/kt-v-calculator
@misc{wecalculate_kt_v_calculator, title = {Kt/V Calculator — Haemodialysis Adequacy (Daugirdas)}, author = {{TG we-Calculate Editorial Team}}, howpublished = {\url{https://we-calculate.com/calculator/kt-v-calculator}}, year = {2026}, note = {TG we-Calculate} }
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