Monitoring aspirin treatment in patients with thrombocytosis: comparison of the platelet function analyzer (PFA)-100 with optical aggregometry.

Aspirin provides satisfactory protection against thrombotic episodes in essential thrombocythemia (ET), but at higher platelet counts has been less effective. Our aim was to compare the platelet function analyzer (PFA)-100 with optical aggregometry in order to determine a reliable method in monitoring aspirin's influence on platelet function in patients with thrombocytosis. We studied 36 patients with thrombocytosis. Sixteen of them, receiving aspirin, composed group A, while group B consisted of 20 patients not taking aspirin. In all patients, we compared the platelet function measured by classic optical aggregation tests with closure times (CT) obtained by the PFA-100. The definition of platelet responses as normal or pathological showed that PFA-100 collagen and/or epinephrine (CEPI) CTs and epinephrine-induced aggregometry is the pair of methods with the higher agreement in monitoring of platelet dysfunction due to ASA treatment (a=94%). Satisfactory results were also obtained for group B (a=81%). The comparison between PFA-100 CEPI CTs and arachidonic acid-induced aggregometry exhibited moderate agreement both in the total number of patients and in group A (a=79% and 94%, respectively). PFA-100 collagen and/or ADP (CADP) CTs and ADP-induced aggregometry were not concordant. The PFA-100 system appears to be a reliable and rapid method in the assessment of aspirin's antiplatelet effect in patients with thrombocytosis. Regarding aggregometry, the selection of the inducer, its concentration and cut-off points is crucial in defining the response to antiaggregating agents. It still remains to determine whether there is any relevance between the measurements obtained by these methods and clinical outcome in thrombocythemic patients.