BUN was measured 1 minute after the end of hemodialysis. The univariate association between urea reduction ratio and body weight was assessed by using Spearman correlation analysis. Patients were sorted by body weight into quartiles and coded with indicator variables from 1 to 4, in ascending order. Analysis of variance was used for between-group comparisons of mean urea reduction ratio, prescribed hemodialysis time, and hemodialyzer urea clearance. Tukey tests were used to test for differences between individual means.
All P values are two-tailed.
Our key findings are that hemodialysis prescriptions given with insufficient attention to individual variation in body mass increase the likelihood of inadequate hemodialysis with increasing body mass and that risk for inadequate hemodialysis is greater in men than in women. These findings were in the context of statistically significant differences in prescribed treatment times and hemodialyzer sizes. Thus, although clinicians attempted to individualize prescriptions, their attempts were grossly inadequate. The mean duration of prescribed hemodialysis in the United States is 3.5 hours three times weekly. The economically forced limitation on prescribing longer dialysis times clearly places persons with large body mass at excess risk for underdialysis.