Kt/V Calculator Daugirdas

How to use this Kt/V dialysis dose calculator

What this calculator does

This calculator estimates single-pool Kt/V from paired blood urea nitrogen measurements using the second-generation Daugirdas approximation, and it also reports the urea reduction ratio (URR). It is designed for checking the arithmetic behind a hemodialysis adequacy estimate, comparing sessions, reviewing a teaching example, or preparing a reproducible calculation for discussion with a dialysis team. Kt/V is a dimensionless estimate of urea clearance normalized to the patient's urea distribution volume; this simplified calculation is not a complete prescription model and does not determine whether an individual patient's dialysis regimen is clinically appropriate. The National Kidney Foundation overview of hemodialysis and adequacy measures explains how Kt/V and URR fit among the other clinical checks used during dialysis care.

When to use it

Use it when you have a matched pre- and post-treatment BUN pair and want to reproduce a single-session spKt/V estimate; when auditing whether a spreadsheet or clinical note used the Daugirdas inputs consistently; when teaching the difference between Kt/V and URR; or when comparing how treatment time or ultrafiltration changes the estimate while the laboratory measurements are held constant. It is not intended for peritoneal dialysis dosing, standardized weekly Kt/V, or personalized treatment recommendations.

How to calculate

1. The calculator opens with a complete demonstration: pre-dialysis BUN 50 mg/dL, post-dialysis BUN 20 mg/dL, 2 hours of dialysis, 2 L of removed ultrafiltrate, and a 70 kg post-dialysis weight. The example results and a validated XLSX workbook are available immediately.
2. Replace each demonstration value with the measurements from one dialysis session. Results update automatically; there is no separate Calculate button.
3. Read Single-pool Kt/V first, then use URR, BUN ratio, Assessment, and the Calculation breakdown to understand how the paired BUN values, treatment time, and fluid removal contributed to the estimate.
4. Select Download Excel to export the current validated inputs and outputs as a real .xlsx workbook. Reset clears the demonstration and all calculated content; after Reset, Download Excel stays disabled until a complete valid input set is entered again.

Input guide

Pre-dialysis BUN is a required positive blood urea nitrogen concentration in mg/dL. Enter a plain decimal-point number such as 50. Higher pre-BUN, with other values fixed, usually lowers the post/pre ratio and can raise the calculated Kt/V. Do not paste units, commas used as decimal separators, or scientific notation into the field. Post-dialysis BUN is the required paired post-treatment value in mg/dL, for example 20. Lower post-BUN generally increases URR and Kt/V; a common mistake is swapping the pre- and post-treatment samples. The ratio must also leave a positive logarithm argument after the treatment-time correction.

Duration of dialysis is required in hours, for example 2. The Daugirdas approximation uses the term 0.008 multiplied by treatment time in hours; entering minutes directly would therefore be a unit error. Volume of removed ultrafiltrate is required in liters and may be zero, for example 2 L. More ultrafiltration increases the volume-correction term when the other inputs remain fixed. Post-dialysis weight is required in kilograms, for example 70 kg. A larger post-treatment weight reduces the relative ultrafiltration fraction UF/W. Use the post-treatment weight, not the pre-treatment weight, because the simplified correction is defined around the post-dialysis value.

Output guide

Single-pool Kt/V is the primary dimensionless estimate. For many people receiving in-center hemodialysis three times weekly, commonly cited guidance uses a minimum delivered spKt/V of 1.2 and a target of 1.4, but an individual's goal can differ. URR is the percentage reduction in BUN and is driven only by the pre/post BUN pair; 0% means no BUN reduction, while a negative URR means the post value exceeded the pre value. BUN ratio is post-BUN divided by pre-BUN; lower ratios correspond to greater urea reduction. Assessment is a compact comparison with the commonly cited 1.2 minimum and 1.4 target for thrice-weekly hemodialysis, not a diagnosis or treatment instruction.

The Calculation breakdown table has three columns: Component names each intermediate, Value shows the current canonical numeric value, and Meaning explains its role. The rows Post/pre BUN ratio (R), 0.008 × treatment time, R – 0.008 × time, UF / post-weight, Volume correction term, Single-pool Kt/V, and URR let you audit the formula step by step. A zero ultrafiltration value is valid and makes the volume correction term zero; invalid or nonfinite inputs clear the result state rather than being silently treated as zero.

Worked example

With the startup values, R = 20 ÷ 50 = 0.4000. The time correction is 0.008 × 2 = 0.0160, so the logarithm argument is 0.3840. The first term is – ln(0.3840) = 0.9571. The ultrafiltration fraction is 2 ÷ 70 = 0.0286, and the volume correction is (4 – 3.5 × 0.4) × 0.0286 = 0.0743. Adding the two terms gives spKt/V = 1.0314, displayed as 1.03. URR is (1 – 0.4) × 100 = 60.00%. This reproduces the standard demonstration calculation while keeping the unrounded model value available for export.

Learn more

The original simplified equation is described in Daugirdas' published equations for monitoring Kt/V. For broader context, the NIDDK hemodialysis guide describes how hemodialysis removes wastes and fluid, while the National Kidney Foundation page linked above explains that adequacy measures are only part of the overall clinical picture.