Background. Microparticles (MPs) are small cell membrane-derived vesicles regarded as both biomarkers and mediators of biological effects. Elevated levels of MPs have previously been associated with endothelial dysfunction and predict cardiovascular death in patients with end-stage renal disease. The objective of this study was to measure change in MP concentrations in contemporary haemodialysis (HD).

Methods. Blood was sampled from 20 consecutive HD patients before and 1h into the HD session. MPs were measured by flow cytometry and phenotyped based on surface markers.

Results. Concentrations of platelet (CD41(+)) (P = 0.039), endothelial (CD62E(+)) (P = 0.004) andmonocyte-derived MPs (CD14(+)) (P<0.001) significantly increased during HD. Similarly, endothelial-(P = 0.007) and monocyte-derived MPs (P = 0.001) expressing tissue factor (TF) significantly increased as well as MPs expressing Klotho (P = 0.003) and receptor for advanced glycation end products (RAGE) (P = 0.009). Furthermore, MPs expressing platelet activationmarkers P-selectin (P = 0.009) and CD40L (P = 0.045) also significantly increased. The increase of endothelial (P = 0.034), monocyte (P = 0.014) and RAGE(+) MPs (P = 0.032) as well as TF+ platelet-derived MPs (P = 0.043) was significantly higher in patients treated with low-flux compared with high-flux dialysers.

Conclusion. Dialysis triggers release of MPs of various origins with marked differences between high-flux and low-flux dialysers. The MPs carry surface molecules that could possibly influence coagulation, inflammation, oxidative stress and endothelial dysfunction. The clinical impact of these findings remains to be established in future studies.