The Kt/V dialysis adequacy calculator uses the Daugirdas second-generation formula to compute single-pool Kt/V (spKt/V) and the urea reduction ratio (URR) from pre- and post-dialysis blood urea nitrogen (BUN), session duration, ultrafiltration volume, and post-dialysis weight. Per KDOQI 2015 guidelines, a minimum delivered spKt/V of ≥1.4 per thrice-weekly session is the adequacy target. An spKt/V below 1.2 warrants urgent prescription review. URR ≥70% is the equivalent benchmarks when weight data are unavailable.
Kt/V & URR Calculator
mg/dL
mg/dL — slow-flow sample within 30 sec
minutes
litres removed during dialysis
kg (dry/target weight)
spKt/V
—
target ≥1.4
URR
—
target ≥70%
Adequacy
—
KDOQI 2015
Daugirdas Formula & KDOQI Targets
spKt/V (Daugirdas 2nd-gen):
R = post-BUN ÷ pre-BUN
t = session duration (hours)
V = post-dialysis weight (kg) — surrogate for urea volume
UF = fluid removed (litres)
Kt/V = −ln(R − 0.008 × t) + (4 − 3.5 × R) × UF ÷ V
URR (%) = (1 − R) × 100
R = post-BUN ÷ pre-BUN
t = session duration (hours)
V = post-dialysis weight (kg) — surrogate for urea volume
UF = fluid removed (litres)
Kt/V = −ln(R − 0.008 × t) + (4 − 3.5 × R) × UF ÷ V
URR (%) = (1 − R) × 100
KDOQI 2015 Adequacy Targets
| Kt/V Range | URR | Interpretation | Action |
|---|---|---|---|
| ≥ 1.4 | ≥ 70% | Adequate | Maintain current prescription; review monthly |
| 1.2 – 1.39 | 65–69% | Borderline | Extend session or increase Qb; recheck next session |
| < 1.2 | < 65% | Inadequate | Urgent prescription review; assess vascular access |
How to Improve Inadequate Kt/V
- Extend session duration — most effective; 30-min extension raises Kt/V ~10–15%
- Increase blood flow (Qb) — from 300 → 350–400 mL/min when access permits
- Increase dialysate flow (Qd) — from 500 → 700–800 mL/min on high-flux dialyser
- Use high-flux dialyser — 1.8–2.1 m² surface area for improved clearance
- Assess vascular access — duplex for recirculation; access recirculation >10% markedly reduces effective Kt/V
- Verify sampling technique — post-BUN must be slow-flow within 30 seconds of session end
- Consider incremental HD — increase frequency to 4×/week for CKD patients with residual renal function
Frequently Asked Questions
What is the Daugirdas second-generation Kt/V formula?
The Daugirdas 2nd-generation spKt/V formula is: Kt/V = −ln(R − 0.008×t) + (4 − 3.5×R) × UF/V, where R = post-BUN/pre-BUN, t = session hours, UF = ultrafiltrate in litres, and V = post-dialysis weight in kg (surrogate for volume of distribution of urea). It corrects for the effect of ultrafiltration and is the most widely validated formula for clinical use.
What is the KDOQI target Kt/V for haemodialysis?
KDOQI 2015 guidelines recommend a minimum delivered spKt/V of ≥1.4 per session for patients on three-times-weekly haemodialysis. An spKt/V of ≥1.2 is the absolute minimum acceptable. The corresponding URR target is ≥70%. For high-frequency or short-daily HD, the eKt/V (equilibrated) target ≥1.2 is used instead.
When should the post-dialysis BUN sample be collected?
The post-dialysis BUN must be drawn using the slow-flow or stop-pump technique — blood flow is reduced to 50–100 mL/min for 15 seconds, then sampled from the arterial port within 30 seconds of session end. Failure to use the slow-flow technique causes falsely high BUN due to access recirculation, artificially inflating the apparent Kt/V.
What is the difference between spKt/V and eKt/V?
spKt/V (single-pool) is calculated directly from BUN measurements taken immediately before and after dialysis. eKt/V (equilibrated) corrects for urea rebound that occurs in the 30–60 minutes after dialysis ends, and is more accurate for short or high-efficiency sessions. A practical approximation is: eKt/V ≈ spKt/V − 0.6 ÷ t (t in hours). eKt/V KDOQI target is ≥1.2.
Can URR replace Kt/V for dialysis adequacy monitoring?
URR is simpler to calculate as it requires no weight data, making it useful for quick adequacy checks. However, URR does not account for convective clearance from ultrafiltration, so it underestimates adequacy in patients with large fluid gains. Kt/V is preferred for formal adequacy assessment. A URR of ≥70% roughly corresponds to an spKt/V of 1.2–1.4, depending on ultrafiltration volume.
Is this Kt/V calculator validated for Indian dialysis patients?
The Daugirdas second-generation formula is validated across diverse populations and is used in KDOQI, ERA-EDTA, and Indian Society of Nephrology guidelines. Indian patients on haemodialysis often have lower body weight and smaller urea volumes, which may affect Kt/V; however, the formula itself requires no population-specific adjustment. The KDOQI spKt/V ≥1.4 target applies universally.
Related Calculators
⚠ Medical Disclaimer: Kt/V calculation requires accurate BUN sampling — post-dialysis sample within 30 seconds using the slow-flow technique. spKt/V is one measure of dialysis adequacy; clinical status, dry weight achievement, intradialytic hypotension, and phosphate/potassium control are equally important. Persistent inadequacy despite prescription optimisation warrants nephrology review and vascular access evaluation. This tool is for healthcare professionals only.