Ultrafiltration Rate Calculation and Clinical Applications in Hemodialysis

Basic Principles and Calculations

The Kidney Disease Outcomes Quality Initiative (KDOQI) recommends calculating ultrafiltration rate (UFR) by dividing the total volume of fluid to be removed by the treatment time, and normalizing this value to body weight to assess cardiovascular stress and mortality risk, with a formula of UFR (mL/h) = Total fluid removal volume (mL) ÷ Treatment time (hours), and weight-normalized UFR (mL/h/kg) = [Total fluid removal (mL) ÷ Treatment time (hours)] ÷ Postdialysis weight (kg) 1

The KDOQI-recommended natural logarithm formula for single-pool Kt/V includes ultrafiltration: spKt/V = -ln(R - GFAC × T) + (4 - 3.5 × R) + (UF/W), where R = ratio of postdialysis to predialysis BUN, GFAC = generation factor, T = treatment time in hours, UF = ultrafiltration volume in liters, and W = postdialysis weight in kilograms, with the generation factor ranging from 0.0045 to 0.0175 depending on treatment frequency 1
An older simplified version of the spKt/V formula uses: spKt/V = -ln(R - 0.008 × t) + (4 - 3.5 × R) + (3 × 0.55 × Weight loss)/V, with weight loss and volume (V) used instead of ultrafiltration volume 2, 3

High ultrafiltration rates (>12.37 mL/h/kg) are independently associated with increased mortality risk, primarily from cardiovascular causes, and when patients require higher fluid removal volumes, treatment duration should be extended or treatment frequency increased rather than accepting excessive UFR 4

Ultrafiltration contributes significantly to total urea clearance in dialysis and must be included in dose calculations, with the ultrafiltration component accounting for a substantial portion of the overall Kt/V value, particularly when fluid removal volumes are large 1, 5