Kt/V Calculator Daugirdas

Created by Łucja Zaborowska, MD, PhD candidate
Reviewed by Steven Wooding
Based on research by
Daugirdas J. T. Simplified equations for monitoring Kt/V, PCRn, eKt/V, and ePCRn Advances in renal replacement therapy (October 1995)See 2 more sources
Sternby, J.; Daugirdas, J. T. Theoretical basis for and improvement of Daugirdas' second generation formula for single-pool Kt/V The International journal of artificial organs (December 2015)Breitsameter, G., Figueiredo, A. E., Kochhann, D. S. Calculation of Kt/V in haemodialysis: a comparison between the formulas Jornal brasileiro de nefrologia : 'orgao oficial de Sociedades Brasileira e Latino-Americana de Nefrologia (March 2012)
Last updated: Nov 16, 2022

The Kt V calculator allows you to assess your patient's dialysis or peritoneal dialysis efficacy and adequacy, using both Urea Reduction Ratio (URR) and the Daugirdas Kt/ V formula.

A short read below will acknowledge you with the basic definitions used in dialysis evaluation and the Kt measurements. We'll also explain the complicated maths that stands behind our simple tool. ⏳

What does Kt/ V stand for in dialysis?

The Kt/ V in dialysis is used for the measurement of the dialysis efficacy. It describes the rate of removal of the excessive fluids/substances (K) in a given treatment (t) of a given patient (V). This index is probably the most popular system to assess the dialysis dose.

The abbreviation itself stands for:

  • K – dialyzer clearance – blood passage
  • t – duration of dialysis in minutes
  • V – volume of body water

This value is dimensionless - is not based on any unit and cannot be calculated using its separate parts and their units.

The Kt/ V system, however, may disadvantage women and smaller people and result in worse dialysis results in these groups of patients - this difference is caused by the variances of their body water content.

Want to know more? How about checking our other kidney-related tools, such as GFR calculator and Urine output calculator?

What is normal Kt/ V?

  • The dialysis is considered efficient when Kt/V is greater or equal to 1.2. That's the minimum value that must be kept at all times. All the values that fall below that range are a sign of the flawed process of hemodialysis therapy.

  • The peritoneal dialysis target Kt/V is equal to 1.7 weekly (according to the International Society of Peritoneal Dialysis).

However, the patient's treatment should be adjusted to the Kt/V values of more than the recommended target!

It's a precaution used to ensure that the process is indeed of appropriate quality - it's crucial since this variable is directly related to the patient's future outcomes and is correlated to survival!

💡 Current guidelines recommend the weekly Kt/V in Acute Kidney Injury to be at least 3.9

The Kt/ V calculator displays your results along with its basic efficacy evaluation.

Our tool requires you to know three fundamental lab findings:

  • Kt/ V urea - both pre and post dialysis level of urea
  • Volume of removed ultrafiltrate

You may read some more about these values using FEUrea calculator and BUN/ creatinine ratio calculator.

Difference between Kt/ V and URR

Kt/ V is considered to be of a better value and more accurate than the URR.

Why is Kt/V better?

Even that both of these values are closely related, the Kt/ V system takes into account two additional variables:

  • Urea removed with the fluid during the dialysis
  • Urea produced by the body during dialysis

The measurement of fluid removed during dialysis using the Kt/ V is also essential because the excessive amount of fluids accumulated in the patients' bodies might cause inevitable harm to their cardiovascular system.

The KDOQI guidelines recommends the Kt/V to be the primary measure of adequacy.

How to calculate Kt/ V in dialysis?

Our standard Kt/ V calculator uses the following equation:

Kt/V = -ln((Post BUN/Pre BUN)- 0.03) + (4 - 3.5 × (Post BUN/Pre BUN)) × (UF/Weight)

Where:

  • Post BUN means the level of post-dialysis Blood Urea Nitrogen, given in milligrams per deciliter (mg/dL).

  • Pre BUN means the level of pre-dialysis Blood Urea Nitrogen, given in milligrams per deciliter (mg/dL).

  • UF stands for the volume of removed ultrafiltrate, given in liters (L).

  • Weight stands for the post-dialysis weight of a subject, given in kilograms (kg).

  • ln stands for the logarithm with the base of 2 → the natural logarithm.

Remember: all multiplications and divisions have a priority over adding and subtractions and should always be calculated first.

Łucja Zaborowska, MD, PhD candidate
Pre-dialysis BUN
mg/dl
Post-dialysis BUN
mg/dl
Duration of dialysis
hrs
Volume of removed ultrafiltrate
liters
Post-dialysis weight
lb
Kt/V
URR
%
💡 If you're looking for more information on the URR, try the URR calculator.
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