[The assessment of platelet function in patients with essential thrombocythemia]

Essential thrombocythemia (ET) is associated with an increased risk of both thromboembolic and bleeding complications. Changes in platelet count and function are crucial but leukocyte activation is also suspected. The aim of the study. The study was designed to assess platelet function by optical and impedance platelet aggregometry and also PFA-100 analyser in ET patients at the time of diagnosis

The tests were performed in 32 ET patients. In each patient platelet aggregation tests by optical (in platelet rich plasma) and impedance methods (in whole blood) after stimulation with ADP, collagen, epinephrine were done. The platelet function was also assessed by PFA-100 method. The control group consisted of 20 healthy volunteers.

In optical platelet aggregometry different platelet function abnormalities were seen in 31 patients (97%). The most frequent was decreased aggregation (19/32) with all used agonists but especially with epinephrine. Spontaneous aggregation was observed in 10 cases and in one we observed hyperaggregation. In whole blood platelet aggregometry abnormal results concerned 23 patients (72%). The most typical (14/32) was hyperactivity of platelets (especially after ADP). In this method we noted spontaneous aggregation in patients and in 4 patients' diminished aggregation. Mixed aggregation disturbances were observed in 6 patients. The closure time in the cohort of patients was significantly prolonged with both cartridges in comparison to control group and was outside reference ranges in 25/32 patient. No significant correlation between values of platelet aggregation in platelet rich plasma and in whole blood was found. No significant differences were observed between ET patients with and without clinical symptoms of bleeding/thrombosis although closure time with both cartridges was longer in patients with bleeding.

In majority of ET patients different platelet function abnormalities are present. The platelet aggregation results depend on environment in which tests are performed. The PFA-100 seems to be a good method for detection of platelet defects in ET.