Dialysis Dose (Kt/V) Calculator

How to Use the Calculator

1. Enter the Post-dialysis weight in kilograms — this is the patient's estimated dry weight at the end of the session.
2. Enter the Ultrafiltration volume in liters — the total fluid removed during the treatment.
3. Enter the Predialysis BUN value drawn before the session starts, and select the unit (mg/dL or mmol/L) from the dropdown next to the field.
4. Enter the Postdialysis BUN value drawn at the end of the session, again selecting the matching unit. The calculator converts mmol/L values to mg/dL automatically.
5. Read the Kt/V result, rounded to three decimal places, below the inputs.

Note: the postdialysis BUN must be lower than the predialysis BUN; otherwise the calculator reports an error, since a rising or unchanged BUN cannot yield a meaningful dialysis dose.

What Is Kt/V and Why Does It Matter?

Kt/V is a dimensionless number that quantifies how effectively a dialysis session clears urea from the body. It is the product of dialyzer urea clearance \(K\) (mL/min) and treatment time \(t\) (minutes), divided by the patient's urea distribution volume \(V\) (approximately equal to total body water). A Kt/V of 1.0 means the equivalent of the entire urea distribution volume was cleared once during the session — in practice, slightly less removal is achieved because urea rebounds between compartments after treatment ends.

Because it is normalized to body size, Kt/V allows meaningful comparison of dialysis dose between patients of different weights and between different treatment prescriptions (shorter vs. longer sessions, smaller vs. larger dialyzers). Large clinical trials such as HEMO and NCDS established Kt/V as the primary measure of hemodialysis adequacy, and guidelines from the National Kidney Foundation (KDOQI) recommend a minimum single-pool Kt/V of 1.2 per session for patients on thrice-weekly hemodialysis, with a target of about 1.4 to provide a safety margin.

Interpreting the result is straightforward: values below 1.2 suggest underdialysis and are associated with higher mortality, malnutrition, and persistent uremic symptoms; values between roughly 1.2 and 1.4 are considered adequate; and very high values achieved by excessively long or fast treatments may cause hypotension and disequilibrium without adding clinical benefit. A single Kt/V value should always be interpreted alongside the patient's symptoms, nutrition, and trend over multiple sessions rather than in isolation.

Assumptions, Limitations, and Practical Tips

• Post-dialysis sampling matters. The formula assumes the postdialysis BUN is drawn with the slow-flow or stop-pump technique immediately at the end of treatment. Sampling too late (after urea rebound) or too early overestimates or underestimates the true dose.
• Single-pool model. The Daugirdas II formula gives single-pool Kt/V (spKt/V). Equilibrated Kt/V (eKt/V), which accounts for post-treatment urea rebound, is typically 0.15–0.20 lower.
• Steady-state assumptions. The calculation assumes a stable patient without major residual kidney function contributions, large urea generation shifts, or missed sessions. In peritoneal dialysis, weekly Kt/V is used instead, and this formula does not apply.
• Residual renal function. Patients with substantial remaining native kidney clearance may achieve good outcomes at a lower delivered dialysis Kt/V, because total urea clearance includes renal clearance.
• Clinical use only as an estimate. This tool supports quick assessment and teaching; formal adequacy assessment should use validated laboratory measurement protocols and clinical judgment.

For related bedside calculations, see the Clinical Dehydration Scale for assessing fluid status, the Half-Life Time calculator for understanding first-order elimination kinetics like urea clearance, and the Mean Arterial Pressure calculator for hemodynamic monitoring during treatment.