Sex- and age-specific prognostic significance of dialysis dose (Kt/V): a nationwide prospective cohort study

Abstract Background Kt/V is the most widely used index for assessing dialysis adequacy in maintenance hemodialysis. Because it normalizes urea clearance to the urea distribution volume, its numerical value is influenced by body size and composition. Whether the association between Kt/V and mortality differs according to sex and age remains uncertain. We therefore investigated this association using a nationwide dialysis registry. Methods We conducted a prospective cohort study using the 2010 Japanese Renal Data Registry linked to one-year outcomes in 2011. A total of 169,963 adults receiving HD or HDF three times weekly were included. Single-pool Kt/V (spKt/V) was analyzed as both a categorical and continuous variable. Associations with all-cause mortality and interactions with sex and age group (< 55, 55–64, 65–74, and ≥ 75 years) were evaluated using multivariable Cox proportional hazards models and restricted cubic splines. Results Among 169,963 patients, 11,866 deaths occurred. Women had higher mean spKt/V than men in every age group. Compared with spKt/V 1.2–<1.4, the adjusted hazard ratio was 1.23 (95% confidence interval, 1.17–1.30) for spKt/V < 1.2 and 0.67 (0.62–0.72) for spKt/V ≥ 1.8. The spKt/V association differed by sex and age group (both interaction P < 0.001). Restricted cubic splines showed an inverse association without an upward turn at high spKt/V; the decline was steeper in women. Findings were consistent in the HD-only sensitivity analysis. Conclusions The association between spKt/V and all-cause mortality varied according to sex and age. These findings suggest that sex and age provide relevant context when interpreting spKt/V, but they do not establish subgroup-specific treatment targets or a causal effect of increasing dialysis dose.