How it's calculated
Kt/V = -ln(R - 0.008×t) + (4 - 3.5×R) × UF/W, where R = post-dialysis BUN ÷ pre-dialysis BUN, t = session length in hours, UF = ultrafiltration volume in litres, and W = post-dialysis weight in kg (Daugirdas second-generation equation).
Interpretation
| Kt/V | Interpretation |
|---|---|
| < 1.2 | Below KDOQI target — consider reviewing prescription |
| ≥ 1.2 | Meets KDOQI minimum target (thrice-weekly schedule) |
Clinical use
- Used to assess whether a haemodialysis prescription is delivering an adequate dialysis dose, guiding adjustments to session length, blood/dialysate flow rates, or dialyser choice.
- KDOQI guidelines recommend a minimum single-pool Kt/V of 1.2 per session on a thrice-weekly schedule; targets differ for other schedules (e.g. more frequent or nocturnal dialysis).
- Kt/V should be measured periodically (e.g. monthly) as part of routine dialysis adequacy monitoring, not assumed to remain constant as access, residual renal function, or prescription change.
- This calculator uses the single-pool Daugirdas formula; equilibrated Kt/V (eKt/V), which accounts for post-dialysis urea rebound, gives a slightly lower value and is preferred by some centres.
Frequently asked questions
What is Kt/V used for?
It quantifies haemodialysis adequacy — how effectively a dialysis session clears urea — used to guide adjustments to the dialysis prescription.
What is a target Kt/V?
KDOQI guidelines recommend a minimum single-pool Kt/V of 1.2 per session for patients on a standard thrice-weekly haemodialysis schedule.
What is the difference between single-pool and equilibrated Kt/V?
Single-pool Kt/V (calculated here via the Daugirdas formula) doesn't account for urea rebound after dialysis ends; equilibrated Kt/V does, and is typically about 0.2 lower than the single-pool value.
How often should Kt/V be measured?
Most centres check it monthly as part of routine dialysis adequacy monitoring, since access function, residual renal function, and prescription changes can all affect delivered dose over time.
References
- Daugirdas JT. Second generation logarithmic estimates of single-pool variable volume Kt/V: an analysis of error. J Am Soc Nephrol. 1993;4(5):1205-1213.
- National Kidney Foundation KDOQI Clinical Practice Guideline for Hemodialysis Adequacy: 2015 Update.