Rebound kinetics of β2-microglobulin after hemodialysis

Background. Evaluation of beta(2)-microglobulin (beta(2)m) removal during hemodialysis using predialysis and immediate postdialysis plasma concentrations is only valid in the absence of postdialysis rebound. Postdialysis rebound of beta(2)m has not been studied extensively, and its importance in the determination of beta(2)m clearance is unknown. Methods. We evaluated the kinetics of urea and beta(2)m in a crossover study of 10 chronic hemodialysis patients using dialyzers with similar urea mass transfer-area coefficients containing either low-flux cellulose acetate or high-flux cellulose triacetate membranes. Kinetics were examined during and following a 210 minute treatment by measuring plasma concentrations predialysis at regular intervals during therapy and at 0, 2, 10, 20, 30, and 60 minutes postdialysis. Clearances of urea and beta(2)m were also determined directly from the arterial and venous concentration differences across the dialyzer at 60 minutes after starting dialysis. Results. By design, urea removal was similar for both low-flux and high-Aux dialyzers as assessed by the urea reduction ratio and Kt/V. Postdialysis urea rebound was similar for low- and high-flux dialyzers; the rebound in the plasma urea nitrogen concentration (expressed as a percentage of the intradialytic decrease in plasma concentration) was 9.2 +/- 1.9% (mean +/- SEM) at 30 minutes postdialysis and 13.0 +/- 1.4% at 60 minutes postdialysis for a single pool urea Kt/V of 1.16 +/- 0.05. The plasma beta(2)m concentration increased by 11.1 +/- 3.0% during the treatment using the low-flux dialyzer but decreased by 27.1 +/- 4.0% during the treatment using the high-flux dialyzer. When using the high-flux dialyzer, the rebound of beta(2)m was 44.8 +/- 21.4% at 30 minute postdialysis and 45.9 +/- 15.9% at 60 minutes postdialysis. The clearance of beta(2)m for the high-flux dialyzer calculated from predialysis and immediate postdialysis plasma concentrations using a single-compartment model (28.2 +/- 4.4 ml/min) was higher (P < 0.05) than that determined directly across the dialyzer (18.3 +/- 2.0 ml/min). If either the 30- or 60-minute postdialysis plasma beta(2)m concentration was used instead, the calculated beta(2)m clearance (16.5 +/- 4.8 ml/min or 15.6 +/- 2.8 ml/min, respectively) was similar to that determined directly across the dialyzer. Conclusions. Postdialysis rebound of beta(2)m when using high-flux dialyzers is substantial; neglecting postdialysis rebound results in an overestimation of beta(2)m clearance when calculated using a single-compartment model.