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Kt/V (Dialysis Adequacy) — Free Online Calculator

Input

mg/dL
mg/dL
L
kg
hours

Kt/V

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Urea Reduction Ratio

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About This Calculator

Kt/V is the primary measure of hemodialysis adequacy. It quantifies the fractional clearance of urea during a dialysis session, where K = dialyzer clearance, t = time, and V = volume of distribution of urea. The Daugirdas second-generation formula accounts for ultrafiltration and urea generation during dialysis. KDOQI guidelines recommend a minimum single-pool Kt/V of ≥ 1.2 for thrice-weekly hemodialysis.

Formula

Kt/V = −ln(R − 0.008 × t) + (4 − 3.5 × R) × UF/W
R = Post-dialysis BUN / Pre-dialysis BUN
t = dialysis time (hours), UF = ultrafiltration (L), W = post-dialysis weight (kg)
URR (%) = (Pre-BUN − Post-BUN) / Pre-BUN × 100

Interpretation

Kt/VURRInterpretation
≥ 1.4≥ 70%Excellent
1.2 – 1.465–70%Adequate (target)
1.0 – 1.260–65%Borderline
< 1.0< 60%Inadequate

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.
  2. KDOQI Clinical Practice Guideline for Hemodialysis Adequacy: 2015 Update. Am J Kidney Dis. 2015;66(5):884-930.

Frequently Asked Questions

What is the minimum acceptable Kt/V?

KDOQI guidelines recommend a minimum single-pool Kt/V (spKt/V) of ≥ 1.2 for patients on thrice-weekly hemodialysis. A target of 1.4 provides a margin of safety. For twice-weekly dialysis, higher targets may be needed.

What factors affect Kt/V?

Kt/V can be improved by: increasing dialysis time (t), using a larger or more efficient dialyzer (K), increasing blood flow rate, increasing dialysate flow rate, or improving vascular access function. Reducing V (patient body water) also increases Kt/V, but this is not a treatment target.

What is the difference between single-pool and equilibrated Kt/V?

Single-pool Kt/V (spKt/V) assumes urea is distributed in one compartment and overestimates delivered dialysis. Equilibrated Kt/V (eKt/V) accounts for urea rebound after dialysis and is lower than spKt/V. The Daugirdas formula calculates spKt/V.

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⚠ Medical Disclaimer

This tool is for educational and informational purposes only. It is not intended to replace professional medical advice, diagnosis, or treatment. Always consult a qualified healthcare professional for clinical decisions.