Kt/V underestimates the hemodialysis dose in women and small men

Current guidelines suggest a minimum Kt/V of 1.2 for three weekly hemodialysis sessions; however, using V as a normalizing factor has been questioned. Parameters such as weight^0.67 (W0.67) and body surface area (BSA) that reflect the metabolic rate may be preferable. To determine this, we studied 328 hemodialysis patients (221 male) with a target Kt/V of 1.2. Using this relationship and the individual's Watson Volume, we calculated the Kt, Kt/BSA, and Kt/W^0.67 equivalent to the target and measured the effects of body size and gender on these parameters for each patient. The target corresponded to a range of equivalent Kt/BSA and Kt/W^0.67 each significantly higher in males than females and in larger than smaller males. V/BSA and V/W^0.67, the conversion factors of Kt/V to Kt/BSA and Kt/W^0.67 respectively, were significantly greater in males than females and heavier than lighter men. Our study shows that if Kt/BSA and Kt/W^0.67 reflect the true required dose, prescribing a target Kt/V of 1.2 would underestimate this in females and in small males. Further work is required to develop clinical outcome-based adequacy targets.