π« Kt/V Dialysis Adequacy Calculator
Daugirdas second-generation Kt/V for hemodialysis.
For informational purposes only, not medical advice. Consult a healthcare professional.
Kt/V measures dialysis adequacy: K (dialyzer urea clearance) times t (time), divided by V (the patient's urea distribution volume, roughly total body water). It answers how much of a full body-water volume was cleared of urea during the session. KDOQI guidelines set the minimum single-pool Kt/V at 1.2, with 1.4 as the target.
Enter pre- and post-dialysis BUN, session hours, liters of fluid removed, and post-dialysis weight. The calculator applies the Daugirdas second-generation formula, the clinical standard, and reports Kt/V plus the urea reduction ratio.
How to Use This Calculator
Use the pre-dialysis BUN and the post-dialysis BUN drawn per your unit's protocol (timing matters because of urea rebound). Enter the actual hours dialyzed, the ultrafiltration volume in liters, and the post-dialysis weight in kg. Read Kt/V against the 1.2 minimum and discuss shortfalls with your nephrologist, not by extending sessions on your own.
Enter pre- and post-dialysis BUN in mg/dL.
Enter session hours, UF liters removed, and post weight in kg.
Read single-pool Kt/V and URR.
Compare against 1.2 minimum / 1.4 target and review with your care team.
The Daugirdas Formula
R = post-BUN / pre-BUN
The logarithmic term captures urea removal: the deeper the BUN ratio drops, the higher the Kt/V, with a small correction (0.008 x t) for urea generated during the session itself. The second term credits ultrafiltration: removing fluid convects extra urea, scaled by body weight. Daugirdas validated this against formal urea kinetic modeling, and it stuck because it needs only routine labs instead of dialysate collection. URR, the simpler sibling metric, is just 1 minus R as a percent; guidelines want URR at least 65%, which roughly corresponds to Kt/V 1.2.
Worked Example
Pre BUN 60, post 18, 4 hours, 2.5 L removed, 70 kg: Kt/V comes out 1.42, comfortably above the spKt/V >= 1.2 (target 1.4) minimum, with a URR of 70.0%. Shorten the session to 3 hours with the same BUN drop and Kt/V falls toward 1.1, which is exactly why time on the machine matters as much as the lab numbers.
Reading Your Kt/V
At or above 1.2, the prescription meets the adequacy minimum; 1.4 is the aiming point. Below 1.2, the usual fixes are longer sessions, higher blood flow, a larger dialyzer, or checking access recirculation, decided by the nephrologist. Note the formula's blind spots: it measures small-solute clearance only, so a good Kt/V does not guarantee good phosphate control or well-being, and very large or small patients need clinical interpretation beyond the number.
Your Dialysis Team Owns the Prescription
Never change session length, blood pump speed, or dialyzer on calculator output. Low Kt/V has many causes, including access dysfunction that needs hands-on evaluation. If you feel persistently washed out, itchy, or unwell despite adequate Kt/V, say so: adequacy numbers and patient experience are both data. For informational purposes only, not medical advice. Consult a healthcare professional.
Related tools: kidney failure risk (KFRE) and mean arterial pressure.
For informational purposes only, not medical advice. Consult a healthcare professional.
Frequently Asked Questions
What is a good Kt/V?
Single-pool Kt/V of at least 1.2 per KDOQI, with 1.4 as the target. Higher within reason is fine; the minimum is the floor, not the goal.
What is the difference between Kt/V and URR?
URR is the simple percent BUN drop; Kt/V adds corrections for urea generation during dialysis and ultrafiltration. Kt/V 1.2 roughly equals URR 65%.
Why did my Kt/V drop suddenly?
Common causes: shortened sessions, lower blood pump speed, access recirculation, a smaller dialyzer, or lab timing issues. Report it rather than compensating yourself.
Does a good Kt/V mean I feel well?
Not necessarily. Kt/V measures small-solute clearance only; phosphate, anemia, fluid balance, and nutrition drive symptoms too.
What is equilibrated Kt/V?
A version correcting for urea rebound after dialysis, always a bit lower than single-pool. Most US units report single-pool for routine adequacy.
How is V estimated?
Roughly total body water: about 55-60% of body weight, adjusted for sex and body composition. The formula uses post-dialysis weight as the practical input.
Can Kt/V be too high?
Extremely high values usually flag measurement error (e.g., wrong post BUN timing) rather than over-dialysis. Clinicians investigate rather than celebrate.
Do home dialysis patients use Kt/V?
Yes, with targets adjusted for frequency: more frequent schedules use weekly standardized Kt/V instead of per-session targets.