M+QuickMedCalc
Educational reference only. Not a diagnostic tool. See full disclaimer.
NephrologyspKt/V & URR

Adult Single-Pool Kt/V (Daugirdas II) & URR Calculator

Calculate adult Daugirdas II single-pool Kt/V and URR for one completed intermittent hemodialysis treatment using paired sampling and actual delivered time; no adequacy classification or prescription.

Content updated: View sources

QuickMedCalc is developed and maintained by an independent developer. Medical content is not independently reviewed by a physician.

Formula and medical content are based on the references listed on this page. See sources, About, and Sources and Review Process.

One unit applies to both paired values; a real unit change clears them.

Same completed treatment and same unit as the post sample.

Collected with the organization’s validated post-dialysis sampling protocol.

Liters; zero is a valid reported volume.

kg.

Decimal hours; 3 hours 30 minutes is 3.5.

I confirm that these values describe one completed intermittent hemodialysis treatment and paired samples collected using the organization’s validated protocol.

I confirm the same-session sampling requirement.

About

This page reproduces Daugirdas II single-pool Kt/V and also displays urea reduction ratio (URR) for one completed adult intermittent hemodialysis treatment. The paired pre- and post-dialysis values must come from that same treatment and use the same BUN or urea unit. [1, 3]

The equation uses actual delivered treatment time, net ultrafiltration volume, post-dialysis weight, and the paired post/pre ratio. The result audit exposes R, the logarithm argument, and the UF/W correction; these are completed-treatment data, not a proposed prescription. [1, 2]

It is not a dialysis prescription and does not calculate equilibrated Kt/V, weekly standard Kt/V, residual kidney urea clearance, peritoneal dialysis, CRRT, SLED, pediatric dialysis, CMS facility performance, or a complete dialysis-quality assessment. [2, 6]

Formula

R = post-dialysis BUN or urea ÷ pre-dialysis BUN or urea. The common unit cancels in this same-session ratio. [1, 3]
spKt/V = −ln(R − 0.008 × t) + (4 − 3.5 × R) × UF ÷ W, where t is actual delivered hours, UF is net ultrafiltration in liters, and W is post-dialysis weight in kilograms. [1]
URR (%) = (1 − R) × 100. URR does not include time or the UF/W correction used by spKt/V. [4]
This implementation keeps full precision internally, displays spKt/V to two decimals and URR to one decimal, and shows audit terms to at most four decimals. Software input limits are not physiologic or treatment ranges.

Interpretation

QuantityMeaningScopeCalculated here
RPost/pre urea or BUN ratioOne completed sessionYes
URRPercentage reduction based only on ROne completed sessionYes
spKt/VDaugirdas single-pool delivered small-solute estimateOne completed sessionYes
eKt/VEquilibrated estimate accounting for post-dialysis reboundOne session with rebound modelingNo
Weekly standard Kt/VFrequency-normalized weekly constructTreatment scheduleNo
Residual kidney urea clearanceNative kidney contribution measured separatelyInterdialytic/weekly contextNo

These quantities are not interchangeable. The same URR can accompany different spKt/V values when delivered time or UF differs, and one spKt/V cannot replace weekly standard Kt/V. This page does not generate an adequacy label, prescription, or CMS submission result.

What each input represents

Pre- and post-dialysis BUN or urea are a same-unit pair from one completed treatment. Actual delivered time is the time completed, not merely the scheduled or prescribed duration. Net UF and post-dialysis weight must also describe that treatment. The confirmation records the same-session and locally validated sampling context; values from different dates, treatments, or units must not be combined.

How the Daugirdas II calculation is assembled

  1. Calculate R as post ÷ pre.
  2. Calculate R − 0.008t.
  3. Confirm that term is greater than zero before taking its natural logarithm.
  4. Calculate −ln(R − 0.008t).
  5. Calculate (4 − 3.5R) × UF/W.
  6. Add the two terms for spKt/V.
  7. Calculate URR separately from R alone.

A logarithm-domain error is a mathematical input-domain failure, not a clinical diagnosis.

Why actual delivered time matters

The formula uses the duration actually completed. Early termination, pauses, or machine interruptions can make delivered time differ from the scheduled or prescribed time. This calculator does not reconstruct machine logs or decide whether a later treatment should be longer.

Why sampling protocol matters

Both samples must come from the same treatment. The pre sample should avoid saline or heparin dilution and incorrect timing after treatment begins. For post sampling, KDOQI describes a slow-flow example of about 100 mL/min, usually for 15 seconds, to reduce access-recirculation effects; validated stop-dialysate-flow protocols may be used by other organizations. Early post sampling can lower post BUN and overestimate URR and Kt/V, while cardiopulmonary recirculation and later urea rebound also affect interpretation. Use the organization's validated method; this page cannot correct these effects from the numbers alone. [3]

spKt/V versus URR

Both begin with the pre/post ratio. URR is a simple percentage, whereas spKt/V also includes delivered time and the UF/W correction. Treatments with the same URR can therefore have different spKt/V values; the two results are related but not interchangeable.

spKt/V, eKt/V, and weekly standard Kt/V

spKt/V is a single-pool estimate. eKt/V models post-dialysis rebound, while weekly standard Kt/V provides a frequency-normalized weekly construct for different schedules. This page calculates only spKt/V and URR and does not infer either omitted quantity from one session. [2]

Worked examples from the implementation

Principal vector

60/20 mg/dL, UF 2.5 L, W 70 kg, t 4 h gives R 0.333333…, log argument 0.301333…, UF/W term 0.101190…, raw spKt/V 1.300728…, displayed 1.30, and URR 66.7%.

Zero UF

The same pair, weight, and time with UF 0 L keeps URR at 66.7% but gives raw spKt/V 1.199538… and display 1.20.

Unit equivalence

BUN 60/20 mg/dL and urea 5/1.6666666666666667 mmol/L produce the same R, spKt/V, and URR when the remaining inputs match.

Second completed treatment

70/20, UF 3 L, W 75 kg, t 4 h gives R 0.285714…, log argument 0.253714…, UF/W term 0.1200, raw spKt/V 1.4915465…, display 1.49, and URR 71.4%.

These examples audit software arithmetic. They are not patient adequacy conclusions or prescriptions for a later treatment.

Static KDOQI context without dynamic labels

KDOQI 2015 gives static context for conventional thrice-weekly HD: target spKt/V 1.4 and minimum delivered spKt/V 1.2. For other frequencies it describes weekly standard Kt/V target 2.3/week and minimum 2.1/week, which this page does not calculate. KDOQI 2006 listed URR minimum 65% and target 70% in its specified context. These are guideline- and schedule-specific reference values, not universal health values; the calculator never labels a submitted result adequate, inadequate, pass, or fail. [2, 4]

Why a higher number is not automatically better

The HEMO trial compared standard and higher dose strategies in thrice-weekly maintenance HD and did not find a major overall benefit from increasing dose substantially beyond then-recommended levels. That does not show that a lower dose is safe or establish one fixed target for every person; this page does not turn “higher” into a treatment recommendation. [5]

Residual kidney function and treatment frequency

Residual kidney urea clearance requires separate measurement and can contribute to formal total-clearance and prescription frameworks. This page has no urine collection, interdialytic data, or weekly model. A high session value cannot establish that treatment may be shortened, and a low value cannot determine how a prescription should change. [2]

Kt/V is not the whole dialysis assessment

This small-solute estimate does not evaluate volume status, blood pressure, intradialytic symptoms, nutrition, anemia, potassium, acid-base status, phosphorus, middle molecules, protein-bound toxins, vascular access, adherence, residual kidney function, or quality of life.

CMS quality-measure context

Current CMS ESRD QIP PY 2027–2028 materials include a Kt/V Dialysis Adequacy topic, with adult HD, adult PD, pediatric HD, and pediatric PD handled as distinct measures. CMS measures have formal denominators, exclusions, aggregation, facility reporting, and payment-year specifications. This calculator reproduces one adult HD session's Daugirdas II arithmetic; it is not a CMS facility-measure calculator and produces no compliance, facility score, submission, or payment conclusion. [6]

When the estimate may be unreliable

  • Pre/post values are from different treatments or use mixed units.
  • The pre sample is diluted by saline or heparin, or the post sample is too early.
  • Access or cardiopulmonary recirculation and post-dialysis rebound affect the pair.
  • Delivered time, UF, or post weight is recorded incorrectly or comes from another session.
  • The treatment was interrupted, not completed, or uses an atypical schedule.
  • A one-session result is applied to PD, CRRT, SLED, pediatric dialysis, or a weekly prescription.

References

  1. 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. PMID 8305648. DOI 10.1681/ASN.V451205.
  2. National Kidney Foundation. KDOQI Clinical Practice Guideline for Hemodialysis Adequacy: 2015 Update. Am J Kidney Dis. 2015;66(5):884–930. PMID 26498416. DOI 10.1053/j.ajkd.2015.07.015.
  3. KDOQI 2006 Hemodialysis Adequacy Guideline 3. Methods for Postdialysis Blood Sampling.
  4. KDOQI 2006 Hemodialysis Adequacy Guideline 4. Minimally Adequate Hemodialysis.
  5. Eknoyan G, et al. Effect of Dialysis Dose and Membrane Flux in Maintenance Hemodialysis. N Engl J Med. 2002;347:2010–2019. PMID 12490682. DOI 10.1056/NEJMoa021583.
  6. Centers for Medicare & Medicaid Services. ESRD Quality Incentive Program — Measuring Quality. Current PY 2027–2028 measure domains.

FAQ

Related Calculators

eGFR

Estimate adult race-free indexed glomerular filtration rate (eGFR) with 2021 CKD-EPI creatinine, 2012 cystatin C, or 2021 combined equations.

CrCl

Estimate adult Cockcroft–Gault creatinine clearance in mL/min from an explicit weight basis, without automatic weight selection or a dosing recommendation.

UPCR / PCR

Calculate a same-specimen spot urine total protein-to-creatinine ratio in mg/mg, mg/g, and mg/mmol; not ACR, 24-hour protein, or a diagnosis.

Disclaimer

Educational and informational reference only. Not intended to replace professional medical advice, diagnosis, treatment, or independent verification.