Background/aims: The mechanism behind the uremic hyperhomocysteinemia has not been elucidated. Possibly, dialyzable uremic toxins play a role, e.g. as enzyme inhibitors. If so, the conditions for enzymatic removal would be expected to improve after dialysis. Therefore, we studied the postdialytic pattern of the plasma total homocysteine (tHcy) concentration.

Methods: We collected blood samples from 19 stable, vitamin-supplemented hemodialysis patients before and at 5, 60, as well as at 480 min after a dialysis session. The patients were studied after dialysis with a low-flux dialyzer (Polyflux 6L) and a high-flux dialyzer (Polyflux 14S).

Results: The mean predialytic plasma tHcy concentration was 13.3 micromol/l which is considerably lower than the concentrations observed in our previous studies. In all patients, the plasma tHcy concentration fell during treatment with both types of dialyzers (average decrease 28 +/- 7%, p < 0.0001, and 31 +/- 8%, p < 0.0001, respectively). No postdialytic change in the plasma tHcy concentration was observed at 60 min after low-flux dialysis, however, after high-flux dialysis, the plasma tHcy concentration was significantly lower at 60 min postdialysis than at 5 min (3 +/- 8%, p < 0.05). At 480 min after dialysis, a significant postdialytic increase in the plasma tHcy concentration was found (6 +/- 9%, p < 0.01, and 11 +/- 5%, p < 0.0001, respectively) both in the case of low-flux and high-flux treatment.

Conclusion: In the postdialytic phase, we observed a short-lived stability in the plasma tHcy concentration, and in the case of high-flux dialysis, even a slight decrease in the plasma tHcy concentration. The results support the hypothesis that dialyzable substances interfere with homocysteine removal.