Abstract: In end-stage renal disease, particularly when treated with haemodialysis, the function of platelets,coagulation and fibrinolytic systems can be disturbed; those patients may show both thrombotic complications and bleeding abnormalities. Thus, it is essential to investigate haemostatic alterations in patients on hemodialysis so that adequate regime for anticoagulant therapy could be implemented. Haemostatic changes in patients on hemodialysis may result from alterations in vessel wall integrity and platelet function, and reduced blood flow in the native arteriovenous fistula. We study the haemostatic abnormalities associated with thrombosis in long term hemodialytic patients to determine whether coagulation and fibrinolysis are enhanced or not in 42 uremia patients on chronic regular hemodialysis treatment (20 of them had history of thrombotic events "group I" and the remaining 22 patients showed no history of thrombosis" group II") and 20 apparently health control group. Plasma levels of some blood coagulation fibrinolysis parameters were measured including platelet count, prothrombin time/concentration (PT/PC), activated
partial thromboplastin time (aPTT), thrombin time (TT), fibrinogen and D-Dimer, platelet aggregation (induced by adenosine diphosphate, collagen, Ristocetin, and Arachedonic acid), and the levels of natural anticoagulant protein C, protein S and antithrombin-III (AT-III). The mean platelet count was normal in all studied groups, while higher mean value of platelet count was observed among patients in group I than group II. Prolonged PT/sec., aPTT/sec and TT in patients groups were observed; those differences were statistically highly significant in comparison with healthy controls (p < 0.001). The mean plasma fibrinogen (g/l) concentration was normal in all groups although levels above normal limits were noted in group I, fibrinogen level was significantly higher (p < 0.05) in group I patients than in normal controls. The mean value of D-dimer (ng/ml) was significantly higher in group I than group II and in comparison with control group (p < 0.001). We did not find differences between group I patients and control group as regard platelet aggregation induced with all agents, while there were statistically significant difference were observed between group II and control except for collagen. In contrast, the level of natural anticoagulants (protein C, protein S and AT III) were significantly reduced in patients groups than control and they were statistically significant, and the levels were lower in group I than group II. In conclusion, our results showed that the long term haemodialysis procedure affects the haemostatic process and may contribute to a thrombotic tendency. Careful weighing of risks and benefits of pharmacological prevention of thrombosis in patients on hemodialysis is crucial and this area certainly warrants further investigation