Dialysis Adequacy Calculator
Calculate single-pool Kt/V, weekly standard Kt/V, and Urea Reduction Ratio (URR) to assess hemodialysis adequacy using the Daugirdas second-generation formula.
About this calculator
This calculator computes the Urea Reduction Ratio (URR), the single-pool Kt/V (spKt/V) using the Daugirdas second-generation formula, and the weekly standard Kt/V (stdKt/V). The per-session equation is spKt/V = -ln(R - 0.008 x t) + (4 - 3.5R) x (UF/W), where R is the post-dialysis to pre-dialysis BUN ratio, t is session length in hours, UF is ultrafiltration volume in liters, and W is post-dialysis body weight in kg. The natural-log term captures the dominant urea-clearance effect of the treatment; the (4-3.5R) x UF/W correction term adjusts for additional urea removed by convective clearance (ultrafiltration) rather than diffusion alone, and for the fact that a larger post-dialysis body weight dilutes that ultrafiltration correction's relative contribution. Per the KDOQI (Kidney Disease Outcomes Quality Initiative) 2015 Clinical Practice Guideline for Hemodialysis Adequacy, the RECOMMENDED TARGET is a delivered spKt/V of >= 1.4 per session (thrice weekly), with a spKt/V of >= 1.2 as the absolute MINIMUM acceptable dose (Grade 1B recommendation) -- this calculator's Adequacy Assessment names which of those two thresholds a session clears.
Weekly Kt/V is reported on the standard-Kt/V scale KDOQI itself uses (target 2.3, minimum delivered 2.1), not as three times the single-session value: spKt/V is first corrected for post-dialysis urea rebound with the Daugirdas rate equation, then converted with Leypoldt's standard-Kt/V equation for three sessions a week. Because the log term is undefined once R falls to or below 0.008 x t, an entered post-dialysis BUN low enough to imply a urea reduction above roughly 97% returns no Kt/V at all rather than a false "below minimum" verdict. This tool is educational and does not replace clinical judgment by a nephrologist or dialysis care team.
Inputs
Results
Single-Pool Kt/V
1.37
Adequacy Assessment
Meets the KDOQI minimum (spKt/V ≥ 1.2) but below the 1.4 target
Figures current as of 2015. Source: Rocco MV, Daugirdas JT, Depner TA, et al., National Kidney Foundation KDOQI Clinical Practice Guideline for Hemodialysis Adequacy: 2015 Update, American Journal of Kidney Diseases, 66(5):884-930
How to Use This Calculator
- Enter the pre-dialysis BUN (blood urea nitrogen) in mg/dL.
- Enter the post-dialysis BUN after the treatment session.
- Input the dialysis session duration in hours.
- Enter the ultrafiltration volume in liters removed during treatment.
- Enter the pre-dialysis body weight in kg.
- Read Single-Pool Kt/V against KDOQI's 1.2 per-session minimum and 1.4 target, and Weekly Standard Kt/V against KDOQI's 2.1 minimum delivered / 2.3 target — do not compare the weekly figure with the per-session thresholds, they are different scales.
How the result changes with Pre-Dialysis Urea (mg/dL)
| Pre-Dialysis Urea (mg/dL) | Single-Pool Kt/V | Adequacy Assessment |
|---|---|---|
| 40 | 0.59 | Below the KDOQI minimum (spKt/V < 1.2) |
| 60 | 1.04 | Below the KDOQI minimum (spKt/V < 1.2) |
| 120 | 1.85 | Meets the KDOQI target (spKt/V ≥ 1.4) |
| 200 | 2.5 | Meets the KDOQI target (spKt/V ≥ 1.4) |
What each input means
- Pre-Dialysis Urea (mg/dL)
- Blood urea nitrogen level before dialysis session.
- Post-Dialysis Urea (mg/dL)
- Blood urea nitrogen level after dialysis session. Must stay above 0.008 × session hours × the pre-dialysis value, or the Daugirdas formula has no value (a urea reduction above ~97%).
- Dialysis Time (hours)
- Duration of the dialysis session.
- Ultrafiltration Volume (liters)
- Volume of fluid removed during dialysis.
- Pre-Dialysis Weight (kg)
- Patient weight before the dialysis session.
What each result means
- Single-Pool Kt/V
- KDOQI minimum acceptable: >= 1.2 per session; the recommended target is >= 1.4 for thrice-weekly hemodialysis. Blank when the entered BUN pair falls outside the formula's domain.
- Adequacy Assessment
- Which KDOQI per-session threshold this delivered dose clears.
- Weekly Standard Kt/V (3×/week)
- KDOQI standard Kt/V: target 2.3, minimum delivered 2.1. This is stdKt/V (Leypoldt, via the Daugirdas rebound correction) — not three times the single-session value.
- Urea Reduction Ratio
- Target: >= 65%.
How this is calculated
Worked example, using the default values
- Identify Input Parameters5 parametersPre-Dialysis Urea (mg/dL) = 80, Post-Dialysis Urea (mg/dL) = 25, Dialysis Time (hours) = 4, Ultrafiltration Volume (liters) = 2.5, Pre-Dialysis Weight (kg) = 75 = 5 input(s) provided
- Urea Reduction RatioURR = (pre − post) / pre × 100(80 − 25) / 80 × 100 = 68.75%
- Single-Pool Kt/V (Daugirdas 2nd generation)spKt/V = −ln(R − 0.008t) + (4 − 3.5R) × UF/WR = 0.313, t = 4 h, UF = 2.5 L, W(post) = 72.5 kg = 1.37
- Weekly Standard Kt/V (Leypoldt, 3 sessions/week)eKt/V = spKt/V − 0.6(spKt/V / t) + 0.03; stdKt/V = [10080(1 − e^−eKt/V)/t] / [(1 − e^−eKt/V)/eKt/V + 10080/(N·t) − 1]t = 240 min, N = 3 = 2.16
- Compare Against KDOQI ThresholdsspKt/V ≥ 1.4 target, ≥ 1.2 minimum (thrice-weekly hemodialysis)1.37 vs 1.2 / 1.4 = Meets the KDOQI minimum (spKt/V ≥ 1.2) but below the 1.4 target
Figures and sources
- KDOQI per-session (spKt/V 1.2 minimum / 1.4 target) and weekly standard Kt/V (2.1 minimum / 2.3 target) hemodialysis adequacy thresholds (2015) — Rocco MV, Daugirdas JT, Depner TA, et al., National Kidney Foundation KDOQI Clinical Practice Guideline for Hemodialysis Adequacy: 2015 Update, American Journal of Kidney Diseases, 66(5):884-930
Engine last updated . Checked against 3 independently-derived tests — how we verify calculators. Built by Paul Gunder, a software engineer, not a licensed financial, medical, or legal professional.
Frequently Asked Questions
What's the difference between the KDOQI 'target' and 'minimum' Kt/V, and which one does the Adequacy Assessment check?
KDOQI's 2015 guideline recommends a TARGET delivered spKt/V of >= 1.4 per session for thrice-weekly hemodialysis, with an absolute MINIMUM of >= 1.2 (a Grade 1B recommendation). The Adequacy Assessment names both: it distinguishes a session that clears the 1.4 target from one that clears only the 1.2 floor, so a result that has merely avoided inadequate dialysis is never mistaken for one that hits the recommended dose.
Why is Weekly Standard Kt/V about 2.2 rather than three times the single-session value?
Because weekly dialysis dose is not additive. Standard Kt/V is a continuous-equivalent clearance defined over the whole week, and it accounts for the fact that urea concentration rebounds and re-accumulates between sessions, so three separate treatments do not deliver three times one treatment's worth of weekly clearance. This calculator first corrects spKt/V for post-dialysis rebound with the Daugirdas rate equation, then applies Leypoldt's standard-Kt/V equation for three sessions per week. The result is directly comparable with KDOQI's published weekly figures — a target of 2.3 with a minimum delivered dose of 2.1 — which a simple threefold multiplication is not.
Why does a higher Ultrafiltration Volume (liters) raise Single-Pool Kt/V?
Because the Daugirdas formula includes a correction term, (4 - 3.5R) x (UF/W), that credits additional urea removed by convective clearance -- solute dragged along with fluid as it's pulled across the dialyzer membrane -- on top of the diffusive clearance the main log term already captures. Removing more fluid volume relative to body weight increases that convective contribution, which is why higher ultrafiltration nudges Kt/V upward.
Why did Single-Pool Kt/V come back blank for the values I entered?
The Daugirdas equation takes the natural log of (R - 0.008t), where R is the post/pre BUN ratio and t is session hours, so it is only defined while R stays above 0.008t -- a urea reduction below roughly 97% for a four-hour session. A post-dialysis BUN low enough to break that is outside anything a real hemodialysis session produces and almost always means a transposed or mistyped lab value. Rather than print a number the formula cannot support, or an "inadequate" verdict that would be exactly backwards, the calculator returns no Kt/V and says so.
Is the Daugirdas formula valid for every dialysis schedule and patient?
No. This formula assumes a conventional thrice-weekly, single-pool hemodialysis session, which is what most stable outpatients receive -- KDOQI publishes separate dosing targets and calculation methods for other schedules (once-weekly, more frequent, or home hemodialysis) and for patients with significant residual native kidney function. The standard-Kt/V figure here also assumes a symmetric weekly schedule and no residual kidney clearance. This calculator is an educational estimate for the standard thrice-weekly case; actual dialysis prescriptions should always be set and reviewed by a nephrologist.
Related Calculators
The questions that sit next to this one — chosen by subject, including calculators filed under a different category.
Cardiac Output Calculator
Calculate cardiac output using the Fick equation and stroke volume method. Also estimates cardiac index and systemic vascular resistance.
Biomedical EngineeringVentilator Settings Calculator
Calculate initial ventilator parameters including ideal body weight, tidal volume, respiratory rate, minute ventilation, PEEP, and FiO₂.
NephrologyDialysis Adequacy (spKt/V) Calculator
Single-pool Kt/V from pre/post dialysis BUN.
NephrologyPeritoneal Dialysis Adequacy Calculator
Weekly Kt/V, creatinine clearance, and PET transport classification for peritoneal dialysis.
Biomedical EngineeringProsthetic Socket Sizing Calculator
Calculate prosthetic socket dimensions including circumference reduction, length, wall thickness, and material recommendation based on activity level.
More in Engineering.