Serum beta 2 microglobulin and extracellular fluid volume during haemodialysis

Conflicting results have been published concerning serum beta 2 microglobulin (beta 2-M) kinetics during dialysis with a cuprophane membrane which is not permeable for the protein. We have investigated the hypothesis that the apparent increase of free serum beta 2-M could result from extracellular fluid volume (ECV) contraction. Using inulin, ECV was measured before and 1 h after a dialysis session with a sodium dialysate concentration of 145 mmol/l. Dialysis was performed either with a cuprophane or a high-flux membrane. Transcellular water shift and changes in beta 2-M concentration were calculated from total body water changes (ultrafiltration) and ECV. ECV decreased from a predialysis value of 16.6 +/- 3.51 (mean +/- SD) (24.9% bodyweight) to a postdialysis value of 11.9 +/- 2.11 (19.8% bodyweight). Ultrafiltration was only 3.1 +/- 1.01, indicating concomitant water shift from ECV to intracellular fluid space. A significant decrease in corrected beta 2-M concentration was found for high-flux membranes. However, postdialysis beta 2-M did not change significantly after dialysis with cellulosic membranes. In conclusion, the apparent increase of serum beta 2-M concentration measured during dialysis with cellulosic membranes may be explained by ECV contraction. These results have to be taken into account for any pathogenic mechanism of the beta 2-M-associated amyloidosis occurring in long-term haemodialysed patients.