The role of the extracorporeal circuit in the trapping and degranulation of platelets.

BACKGROUND

Although platelet (PLT) activation and degranulation are well-known phenomena during hemodialysis (HD), controversies still exist about their nature and origin.

METHODS

PLT characteristics [PLT numbers, mean PLT volume (MPV), PLT distribution width (PDW), PLT large cell ratio (p-LCR), immature PLT fraction] and activation status [CD62p expression, platelet factor 4 (PF4) and beta-thromboglobulin (BTG) plasma levels] were estimated in 19 patients before and during HD. Blood was sampled from both the afferent and efferent lines. Additionally, the influence of low-molecular-weight heparin (LMWH) on PF4 and BTG concentrations was analyzed.

RESULTS

CD62p expression increased in the extracorporeal circuit (ECC) in the first 30 min. Simultaneously, PLT numbers dropped markedly within the ECC. MPV, PDW and p-LCR decreased over time. Like CD62p expression, BTG reached peak values at t30, was exclusively released within the ECC and was not influenced by the application of LMWH. In contrast, PF4 was significantly released outside the ECC in response to LMWH.

CONCLUSIONS

PLTs are predominantly activated within the ECC and not on a remote distance. PLTs stick to the ECC, particularly after first passage. BTG is an appropriate marker for HD-induced PLT degranulation, whereas PF4 originates from both activated PLTs and LMWH-induced detachment from the endothelium. PLTs are not exhausted due to the repetitive stimulation of clinical HD. Hence, dialysis modalities with longer duration or greater frequency may be associated with a less beneficial PLT activation profile, which may counteract their clinical benefits.