BLOOD UREA LEVELS 30 MINUTES BEFORE THE END OF DIALYSIS ARE EQUIVALENT TO EQUILIBRATED BLOOD UREA

The steady decline in blood urea during high efficiency hemodialysis i s followed by a rebound phase after dialysis in which the level of ure a rises to an equilibrium value (Ct+30) that may be up to 20% higher t han the immediate post dialysis (C-t) concentration. The artificially low urea concentration immediately after dialysis leads to an overesti mate of the efficiency of the dialysis calculated by Kt/V if the true equilibrium blood concentration of urea is not used in the calculation by the single-pool urea kinetic model. The measurement of equilibrium urea concentration requires a blood sample approximately 30 min after hemodialysis, which is an encumbrance on dialysis patients. This stud y was undertaken to determine whether an intradialytic sample taken 30 min before the end of dialysis (Ct-30) may be representative of the e quilibrium sample, and to compare the Kt/V using the Ct-30 and Ct+30 s amples. Thirty-six patients were studied and blood urea concentrations were measured half an hour before the end of dialysis (Ct-30), at the end of dialysis (C-t), and half an hour after the end of dialysis (Ct +30). Kt/V (Daugirdas method) was calculated using urea concentration 30 min before the end of dialysis (Kt/Vt-30) and was compared with Kt/ V calculated using equilibrium urea concentration (Kt/Vt+30.) There we re no significant differences between the Kt/Vt-30 and the KtV(t+30) ( 1.25 versus 1.22, p = 0.65). The correlation between Kt/Vt-30 and Kt/V t+30 was excellent with r(2) = 0.93, regression y = 1.05 x -0.033. Kt/ Vt-30 also compared favorably with the Kt/V double pool method (Kt/V-d p) described by Daugirdas (1.25 versus 1.19, p = 0.23). Using the Ct-3 0 to calculate Kt/V by the percent urea reduction methods of Jindal (K t/V-pro) decreases the Kt/V value by 0.14 on average, but it remains s ignificantly higher than the Daugirdas method. The authors conclude th at calculations using urea concentration 30 min before the end of dial ysis improves the accuracy of dose estimation in high efficiency dialy sis, without inconveniencing the patient.