An analysis of body weight and hemodialysis adequacy based on the urea reduction ratio

The purpose of this study was to evaluate inadequate hemodialysis risk in patients with body weights in the upper quartile of a sample distribution using the urea reduction ratio (URR). Using a case-control design and a simple random sample (n = 315) of hemodialysis (HD) patients, postdialysis weights were divided into quartiles based with a cut-off value at the upper quartile, which was equal to > 81 kilograms (kg). The dichotomous outcome, URR > 65% and URR < 65% constituted the classification for inadequate dialysis risk. The odds ratio (OR) was used to evaluate inadequate dialysis risk based on this outcome. A multivariate logistic regression model was used to adjust for confounding variables and validated for goodness of fit. Those in the > 81 kg group were given more dialysis session time in minutes and used higher efficiency dialyzers as indicated by the coefficient of ultrafiltration (KUf), yet were more likely to have URRs < 65% compared to other patients in the sample (p < 0.001). This finding persisted in the logistic regression model when simultaneously fitting both gender and dialysis session time. Patients weighing > 81 kg experienced an increased risk of inadequate dialysis when compared to all others (OR 4.02, 95% CI [confidence interval] 2.217-7.29). A postdialysis weight > 81 kg increased the risk of inadequate dialysis for patients in this sample. This effect was confounded by a dialysis time x weight interaction term. Also, women were found to have a lower inadequate dialysis risk compared to men after adjusting for weight classification. We, therefore, conclude that patients who weigh > 81 kg may experience inadequate dialysis despite longer, more efficient dialysis sessions. Longer dialysis sessions may benefit some patients, but the effect in larger patients may not be a uniform response.