Kt/V Calculator – Daugirdas II spKt/V & URR
Calculate adult single-pool Kt/V and URR from paired pre/post BUN or urea, delivered time, ultrafiltration, and post-dialysis weight for one completed intermittent hemodialysis treatment.
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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
Interpretation
| Quantity | Meaning | Scope | Calculated here |
|---|---|---|---|
| R | Post/pre urea or BUN ratio | One completed session | Yes |
| URR | Percentage reduction based only on R | One completed session | Yes |
| spKt/V | Daugirdas single-pool delivered small-solute estimate | One completed session | Yes |
| eKt/V | Equilibrated estimate accounting for post-dialysis rebound | One session with rebound modeling | No |
| Weekly standard Kt/V | Frequency-normalized weekly construct | Treatment schedule | No |
| Residual kidney urea clearance | Native kidney contribution measured separately | Interdialytic/weekly context | No |
- Quantity
- R
- Meaning
- Post/pre urea or BUN ratio
- Scope
- One completed session
- Calculated here
- Yes
- Quantity
- URR
- Meaning
- Percentage reduction based only on R
- Scope
- One completed session
- Calculated here
- Yes
- Quantity
- spKt/V
- Meaning
- Daugirdas single-pool delivered small-solute estimate
- Scope
- One completed session
- Calculated here
- Yes
- Quantity
- eKt/V
- Meaning
- Equilibrated estimate accounting for post-dialysis rebound
- Scope
- One session with rebound modeling
- Calculated here
- No
- Quantity
- Weekly standard Kt/V
- Meaning
- Frequency-normalized weekly construct
- Scope
- Treatment schedule
- Calculated here
- No
- Quantity
- Residual kidney urea clearance
- Meaning
- Native kidney contribution measured separately
- Scope
- Interdialytic/weekly context
- Calculated here
- No
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. Values from different dates, treatments, or units must not be combined.
How the Daugirdas II calculation is assembled
- Calculate R as post ÷ pre.
- Calculate R − 0.008t.
- Confirm that term is greater than zero before taking its natural logarithm.
- Calculate −ln(R − 0.008t).
- Calculate (4 − 3.5R) × UF/W.
- Add the two terms for spKt/V.
- 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]
Other schedules use different Kt/V methods
For schedules other than conventional thrice-weekly HD, KDOQI describes weekly standard Kt/V target 2.3 volumes/week and minimum 2.1 volumes/week using a method that includes ultrafiltration and residual kidney function. This page does not calculate weekly standard Kt/V, and a one-session spKt/V must not be compared with those weekly values. [2]
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
- 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.
- 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.
- KDOQI 2006 Hemodialysis Adequacy Guideline 3. Methods for Postdialysis Blood Sampling.
- KDOQI 2006 Hemodialysis Adequacy Guideline 4. Minimally Adequate Hemodialysis.
- 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.
- Centers for Medicare & Medicaid Services. ESRD Quality Incentive Program — Measuring Quality. Current PY 2027–2028 measure domains.
- National Kidney Foundation. Hemodialysis: How It Works, Types, and What to Expect. Current patient-facing Kt/V and URR context. Accessed September 5, 2026.
FAQ
spKt/V = −ln(R − 0.008 × delivered time) + (4 − 3.5 × R) × net UF ÷ post-dialysis weight, where R is post/pre BUN or urea.
Sources: [1]
URR is (1 − R) × 100. It is a simpler post/pre urea reduction measure and does not include delivered time or the UF/weight correction in spKt/V.
Sources: [4]
Pre samples should avoid saline or heparin dilution, and post samples need the organization’s validated method. Access recirculation, early sampling, cardiopulmonary recirculation, and urea rebound can alter the ratio; this page cannot correct them.
Sources: [3]
KDOQI static context for conventional thrice-weekly HD is target spKt/V 1.4 and minimum delivered 1.2. Current NKF patient guidance says many people receiving in-center HD three times weekly are assessed against Kt/V of at least 1.2 or URR of at least 65%. Goals can differ, other schedules use different methods, and this page applies no labels.
eKt/V accounts for post-dialysis rebound and weekly standard Kt/V describes a different frequency-based construct. Neither is the single-session spKt/V calculated here.
Sources: [2]
This page calculates one adult hemodialysis session. A CMS ESRD QIP measure has separate modality and age specifications, denominators, exclusions, aggregation, facility reporting, and payment-year rules; this page does not calculate a facility score or submission.
Sources: [6]
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Disclaimer
Educational and informational reference only. Not intended to replace professional medical advice, diagnosis, treatment, or independent verification.