Kt/V (Daugirdas Second Generation spKt/V)

What This Calculator Measures

Calculates single-pool Kt/V (spKt/V) for hemodialysis adequacy using the Daugirdas second-generation formula, supporting KDOQI dialysis dosing standards.

How to Use

1. Measure pre- and post-dialysis BUN (mg/dL) on the same treatment.
2. Record the treatment time (hours), ultrafiltration volume (L), and post-dialysis weight (kg).
3. Compute R = post/pre BUN; then spKt/V = −ln(R − 0.008t) + (4 − 3.5R) × UF/W.

How the Calculation Works

Single-pool Kt/V uses the Daugirdas second-generation equation: spKt/V = -ln(R - 0.008 x t) + (4 - 3.5 x R) x (UF / W), where R is the post/pre-dialysis BUN ratio, t is treatment time in hours, UF is ultrafiltrate volume in L, and W is post-dialysis weight in kg.

Variables Explained

Interpretation Guide

KDOQI recommends a minimum delivered spKt/V of 1.2 per treatment (target 1.4) for three-times-weekly hemodialysis. Below 1.0 indicates inadequate dialysis.

Clinical Significance

Dialysis dose is directly linked to patient survival and quality of life. spKt/V is the KDOQI-recommended measure for verifying that patients receive an adequate minimum delivered dose.

When It Is Useful

• Routine monthly hemodialysis adequacy monitoring
• Evaluation after dialysis prescription changes
• Assessment when urea reduction ratio (URR) is borderline
• Pre- and post-access intervention adequacy assessment

When It Is Not Useful

• Peritoneal dialysis — uses weekly Kt/V targets
• Twice-weekly or alternate hemodialysis schedules — different targets apply
• In-center HD with incorrect post-BUN sampling (pump recirculation) without correction

Common Mistakes

• Entering ultrafiltration volume in milliliters instead of liters inflates the ultrafiltrate over weight correction term and distorts the delivered dose.
• Reversing the pre-dialysis and post-dialysis BUN values inverts the R ratio and produces a Kt/V unrelated to the actual treatment.
• Applying the 1.2 minimum to peritoneal dialysis or a twice-weekly schedule uses an adequacy standard that does not apply to that regimen.
• Reporting single-pool Kt/V as though it accounts for urea rebound overlooks that equilibrated Kt/V is the measure that corrects for rebound.

Limitations

• Single-pool estimates do not account for post-dialysis urea rebound (eKt/V does).
• Requires accurate post-dialysis BUN sampling technique.
• Assumes three-times-weekly dialysis; alternative schedules require different adequacy standards.

Worked Example

A 68-year-old man on thrice-weekly hemodialysis: pre-BUN 90 mg/dL, post-BUN 30 mg/dL, ultrafiltrate 2.5 L, treatment time 4 h, post-dialysis weight 75 kg.

Expected Result: R = 30/90 = 0.333; spKt/V = −ln(0.333 − 0.032) + (4 − 1.167) × 2.5/75 ≈ 1.29 — adequate (≥ 1.2).

Evidence & References

Source:

Original derivation (peer-reviewed)

Reference:

Daugirdas JT. J Am Soc Nephrol. 1993;4(5):1205-1213.

Content updated:

2026-08

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. (Original Derivation)
2. National Kidney Foundation. KDOQI Clinical Practice Guideline for Hemodialysis Adequacy: 2015 update. Am J Kidney Dis. 2015;66(5):884-930. (Guideline)

Frequently Asked Questions

Kidney function assessment tools