Dialysis Adequacy (spKt/V) Calculator
Single-pool Kt/V from pre/post dialysis BUN.
About this calculator
This calculator estimates hemodialysis adequacy using the Daugirdas second-generation natural-log formula for single-pool Kt/V (spKt/V) -- published by Dr. John T. Daugirdas in the Journal of the American Society of Nephrology in 1993 to correct the first-generation formula's overestimation at higher Kt/V -- the standard bedside measure of how much urea a dialysis session clears relative to the patient's body urea distribution. It combines the pre- and post-dialysis BUN ratio (R) with session duration and an ultrafiltration correction (fluid removed relative to post-dialysis weight), since fluid removal itself contributes to solute clearance beyond diffusion alone. KDOQI guidance treats spKt/V >= 1.2 as the minimum acceptable delivered dose for thrice-weekly hemodialysis, with 1.4 more often cited as the actual target to build in a safety margin -- this calculator's "Adequacy Met" flag uses the 1.2 minimum, not the higher 1.4 goal.
Equilibrated Kt/V (eKt/V) adjusts spKt/V downward to account for urea rebound after dialysis ends, when urea redistributes from tissue back into blood; the correction used here (a 0.6/session-hours coefficient) is specific to arteriovenous vascular access and would differ for a central venous catheter. Standardized weekly Kt/V (stdKt/V) uses the Leypoldt-Depner equation cited in the KDOQI 2006 guidelines to put weekly clearance on a schedule-independent scale in principle, so thrice-weekly and more-frequent dialysis regimens can in general be compared on the same number -- but this calculator computes it assuming exactly three sessions per week (N=3), a fixed value baked into the formula rather than an input a user can change. It correctly reflects a conventional thrice-weekly patient's stdKt/V, but does NOT generalize to a different actual schedule (more-frequent or nocturnal dialysis): comparing this output against a target for a non-thrice-weekly regimen would require recomputing with the real sessions-per-week value, which this tool does not accept. A commonly cited weekly target is approximately 2.1 for conventional thrice-weekly HD. This calculator does not account for residual native kidney function, which reduces the dialysis dose actually needed, nor does it replace direct urea kinetic modeling for borderline or complex cases.
Medical Disclaimer
This calculator is for informational and educational purposes only. It is not a substitute for professional medical advice, diagnosis, or treatment. Always consult a qualified healthcare provider before making decisions about your health. Never disregard professional medical advice or delay seeking it because of results from this tool.
Inputs
Results
Single-Pool Kt/V
1.3
Figures current as of 1993. Source: 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.
How to Use This Calculator
- Enter pre-dialysis BUN (mg/dL) and post-dialysis BUN (mg/dL) from session labs.
- Enter session duration (hours) and ultrafiltration volume (L) removed during dialysis.
- Enter post-dialysis weight (kg).
- Read the single-pool Kt/V (spKt/V): KDOQI target >= 1.2 for thrice-weekly hemodialysis.
- Check URR (%) — target >= 65% — and whether adequacy was met (1 = yes, 0 = no).
How the result changes with Pre-Dialysis BUN (mg/dL)
| Pre-Dialysis BUN (mg/dL) | Single-Pool Kt/V |
|---|---|
| 30 | 0.51 |
| 45 | 0.97 |
| 90 | 1.78 |
| 150 | 2.42 |
What each input means
- Pre-Dialysis BUN (mg/dL)
- Blood urea nitrogen before dialysis session.
- Post-Dialysis BUN (mg/dL)
- Blood urea nitrogen after dialysis session.
- Session Duration (hours)
- Duration of the hemodialysis session.
- Ultrafiltration Volume (L)
- Volume of fluid removed during dialysis.
- Post-Dialysis Weight
- Patient weight after dialysis.
What each result means
- Single-Pool Kt/V
- Daugirdas 2nd-gen spKt/V. KDOQI target >= 1.2 for thrice-weekly HD.
- Urea Reduction Ratio (URR)
- Percentage reduction in BUN. Target >= 65%.
- Equilibrated Kt/V
- Rate-adjusted Kt/V accounting for urea rebound.
- Adequacy Met (1=Yes, 0=No)
- Whether spKt/V meets KDOQI minimum of 1.2.
- Standardized Weekly Kt/V
- Leypoldt-Depner stdKt/V (KDOQI 2006), computed assuming 3 sessions/week -- valid for conventional thrice-weekly HD only. Commonly cited weekly target is approximately 2.1.
How this is calculated
Worked example, using the default values
- Identify Input Parameters4 parametersPre-Dialysis BUN (mg/dL) = 60, Post-Dialysis BUN (mg/dL) = 20, Session Duration (hours) = 4, Ultrafiltration Volume (L) = 2.5 = 5 input(s) provided
- Calculate Single-Pool Kt/VSingle-Pool Kt/V = -ln(R - 0.008 * sessionTime) + (4 - 3.5 * R) * (ultrafiltration / postWeight)1.301 = 1.301
- Calculate Urea Reduction RatioUrea Reduction Ratio = (1 - R) * 10066.7 = 66.7
- Calculate Equilibrated Kt/VEquilibrated Kt/V = spKtV - 0.6 * (spKtV / sessionTime) + 0.031.136 = 1.136
Figures and sources
- Daugirdas second-generation natural-log formula for single-pool Kt/V (1993) — 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.
Engine last updated . Checked against 1 independently-derived test — 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 spKt/V and eKt/V?
Single-pool Kt/V (spKt/V) is calculated directly from the pre- and post-dialysis BUN measured right at the end of the session. Equilibrated Kt/V (eKt/V) is lower, because it corrects for urea rebound -- in the 30-60 minutes after dialysis stops, urea that was sequestered in tissue redistributes back into the bloodstream, so the true equilibrated clearance is somewhat less than what the immediate post-dialysis numbers suggest.
Is a spKt/V of exactly 1.2 considered adequate dialysis?
It meets KDOQI's minimum acceptable threshold, which is what this calculator's Adequacy Met flag checks, but many nephrology guidelines cite 1.4 as the actual target delivered dose to build in a margin for treatment variability -- missed time, access issues, or lab variation that can push the real delivered dose below what was planned. A result right at 1.2 is a reasonable prompt to review the prescription rather than treat as comfortably sufficient.
Why does removing more fluid during dialysis raise the calculated Kt/V?
The ultrafiltration term in the Daugirdas formula reflects that convective clearance -- solutes carried along with fluid as it's removed -- adds to diffusive urea clearance, so a larger ultrafiltration volume relative to the patient's post-dialysis weight increases spKt/V somewhat, independent of how much the BUN itself dropped. This is a real physiologic contribution, not just a mathematical adjustment.
What is standardized Kt/V (stdKt/V) used for, if spKt/V already measures adequacy?
stdKt/V is designed to put weekly dialysis clearance on a schedule-independent scale, which in principle lets it fairly compare, say, three 4-hour sessions a week against more frequent short daily sessions or nocturnal dialysis. This calculator, however, computes stdKt/V assuming exactly three sessions per week -- it has no input for actual sessions per week, so its stdKt/V output is only valid for a conventional thrice-weekly schedule. It does not generalize to a more-frequent or nocturnal regimen the way the underlying stdKt/V concept is meant to.
Related Calculators
The questions that sit next to this one — chosen by subject, including calculators filed under a different category.
Peritoneal Dialysis Adequacy Calculator
Weekly Kt/V, creatinine clearance, and PET transport classification for peritoneal dialysis.
NephrologyFENa & Urine Indices Calculator
Fractional excretion of sodium, urine anion gap, and renal failure index for AKI workup.
Biomedical EngineeringDialysis 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.
NephrologyDry Weight & Fluid Balance Calculator
Calculate interdialytic weight gain, UF rate, and fluid overload assessment for dialysis patients.
More in Medical & Clinical.