title: Blood urea levels 30 minutes before the end of dialysis are equivalent to equilibrated blood urea.
abstract: The steady decline in blood urea during high efficiency hemodialysis is followed by a rebound phase after dialysis in which the level of urea rises to an equilibrium value (Ct + 30) that may be up to 20% higher than the immediate post dialysis (Ct) concentration. The artificially low urea concentration immediately after dialysis leads to an overestimate 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 study was undertaken to determine whether an intradialytic sample taken 30 min before the end of dialysis (Ct - 30) may be representative of the equilibrium sample, and to compare the Kt/V using the Ct - 30 and Ct + 30 samples. 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 (Ct), 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 were no significant differences between the Kt/Vt - 30 and the KtVt + 30 (1.25 versus 1.22, p = 0.65). The correlation between Kt/Vt - 30 and Kt/Vt + 30 was excellent with r2 = 0.93, regression y = 1.05 x -0.033. Kt/Vt - 30 also compared favorably with the Kt/V double pool method (Kt/Vdp) described by Daugirdas (1.25 versus 1.19, p = 0.23). Using the Ct - 30 to calculate Kt/V by the percent urea reduction methods of jindal (Kt/Vpru) decreases the Kt/V value by 0.14 on average, but it remains significantly higher than the Daugirdas method. The authors conclude that calculations using urea concentration 30 min before the end of dialysis improves the accuracy of dose estimation in high efficiency dialysis, without inconveniencing the patient.
authors.affiliation: University of Toronto, Ontario, Canada.
authors.forename: S
authors.initials: S
authors.lastname: Bhaskaran
authors.forename: S
authors.initials: S
authors.lastname: Tobe
authors.forename: C
authors.initials: C
authors.lastname: Saiphoo
authors.forename: A
authors.initials: A
authors.lastname: Moldoveanu
authors.forename: D S
authors.initials: DS
authors.lastname: Raj
authors.forename: M A
authors.initials: MA
authors.lastname: Manuel
mesh_terms: D005260:Female; D006801:Humans; D007700:Kinetics; D008297:Male; D008875:Middle Aged; D006435:Renal Dialysis; D013997:Time Factors; D014508:Urea / Q000097:blood*
chemical_list: D014508:Urea