[EDTA-dependent pseudothrombocytopenia--differentiation from true thrombocytopenia].

EDTA-induced pseudothrombocytopenia is the phenomenon of in vitro platelet clumping due to autoantibodies that recognize platelet antigens modified by EDTA. The phenomenon is present in both healthy subjects and patients with various diseases and its incidence has been reported to be 0.09 to 0.21%. In the leukocyte histogram provided by automated cell counters, platelet clumps often appear as particles less than 35 fl. In order to confirm EDTA-induced platelet clumping, blood samples anticoagulated with EDTA are analyzed for platelet counts and leukocyte histograms immediately after withdrawal and 60 to 120 minutes later. EDTA-induced pseudothrombocytopenia is diagnosed when platelet number decreases together with the characteristic leukocyte histogram and microscopic detection of platelet aggregates on the blood smear.