Free Kt v dialysis Calculator | nephrology Clinical Decision Support

How it Works

Variable Definitions

K	Dialyzer clearance (mL/min) — the "speed" of cleaning
t	Time (minutes) — the duration of the session
V	Volume of urea distribution (L) — roughly equal to total body water

Daugirdas II Formula (Single-Pool)

Kt/V = -ln(R - 0.008 × t) + (4 - 3.5 × R) × 0.55 × UF/V

Variables in Calculation

R = Post-dialysis BUN / Pre-dialysis BUN

t = Dialysis session time in hours

UF = Ultrafiltration volume (weight loss) in kg

V = Post-dialysis anthropometric volume (L)

Clinical Pearls

The "V" Pitfall

The volume of distribution (V) is often underestimated in amputees or overestimated in patients with significant edema. Errors in V will lead to misleadingly high or low Kt/V scores.

Single-Pool vs. Equilibrated

spKt/V (Single-Pool): Assumes urea is removed from one large tank. It overestimates the true dose because it doesn't account for urea "rebound" from tissues.

eKt/V (Equilibrated): Adjusts for urea rebound. It is typically 0.2 units lower than spKt/V.

Troubleshooting Low Kt/V

01

Check blood flow (Qb) and dialysate flow (Qd) rates.

02

Ensure the dialyzer surface area (size) is appropriate for the patient's size.

03

Assess for access recirculation (e.g., stenosis in fistula/graft).

04

Verify actual treatment time matches prescribed time (no early sign-offs).

Next Steps

Target Thresholds (KDOQI)

Minimum spKt/V	1.2 per treatment
Target spKt/V	1.4 per treatment
Minimum PD Kt/V	1.7 per week (Total)

Management Actions

01

If Kt/V < 1.2: Increase treatment time, increase blood flow rate, or increase dialyzer size.

02

Assess Patient Adherence: Review missed treatments or shortened sessions.

03

Clinical Correlation: If Kt/V is "perfect" but the patient feels uremic, consider middle-molecule clearance issues or alternative toxins.

Related Tools

Urea Reduction Ratio (URR)

Body Surface Area (DuBois)

Normalized Protein Catabolic Rate (nPCR)

The Evidence

Core Guidelines

KDOQI Clinical Practice Guideline for Hemodialysis Adequacy: 2015 update.

National Kidney Foundation • American Journal of Kidney Diseases. 2015;The current gold standard for defining adequacy targets and measurement protocols.

The HEMO Study

Effect of dialysis dose and membrane flux in maintenance hemodialysis.

Eknoyan G et al. • NEJM. 2002;Large RCT showing that doses higher than a Kt/V of 1.3 did not significantly improve survival.

Origins & History

Sargent and Gotch

The Kt/V model was developed by Frank Gotch and John Sargent in the 1980s. It was a revolutionary shift from the "Scribner Rule" (which focused on hours) to a mathematically rigorous assessment of solute clearance.

Mathematical Rationale

The formula is derived from first-order kinetics. Because urea concentration declines exponentially during dialysis, a natural logarithm (ln) is used to linearize the relationship between clearance and concentration.

Kt/V Dialysis

When to Use

When to Use

Clinical Objective

How it Works

Variable Definitions

Daugirdas II Formula (Single-Pool)

Variables in Calculation

Clinical Pearls

The "V" Pitfall

Single-Pool vs. Equilibrated

Troubleshooting Low Kt/V

Next Steps

Target Thresholds (KDOQI)

Management Actions

Related Tools

The Evidence

Core Guidelines

KDOQI Clinical Practice Guideline for Hemodialysis Adequacy: 2015 update.

The HEMO Study

Effect of dialysis dose and membrane flux in maintenance hemodialysis.

Origins & History

Sargent and Gotch

Mathematical Rationale

In Recent Clinical News

Kt/V Dialysis

When to Use

When to Use

Clinical Objective

How it Works

Variable Definitions

Daugirdas II Formula (Single-Pool)

Variables in Calculation

Clinical Pearls

The "V" Pitfall

Single-Pool vs. Equilibrated

Troubleshooting Low Kt/V

Next Steps

Target Thresholds (KDOQI)

Management Actions

Related Tools

The Evidence

Core Guidelines

KDOQI Clinical Practice Guideline for Hemodialysis Adequacy: 2015 update.

The HEMO Study

Effect of dialysis dose and membrane flux in maintenance hemodialysis.

Origins & History

Sargent and Gotch

Mathematical Rationale

In Recent Clinical News