IGG PLATELET ANTIBODIES IN EDTA-DEPENDENT PSEUDOTHROMBOCYTOPENIA BINDTO PLATELET MEMBRANE GLYCOPROTEIN IIB

EDTA-dependent pseudothrombocytopenia (PTCP) consists of an inappropri ate low platelet count caused by autoantibodies present in the serum s amples reacting with platelets only in EDTA-anticoagulated blood. By u sing immunoprecipitation and Wester blot techniques. we studied the im munochemical specificity of platelet agglutinating autoantibodies in t he serum samples of 10 patients with PTCP. Furthermore, to evaluate a possible role of PTCP-associated IgG autoantibodies in increased plate let turnover; we assayed the plasma glycocalicin (GC) level and calcul ated the GC index for every patient. Our results provide direct eviden ce that an epitope located on platelet membrane glycoprotein IIb is re cognized by PTCP-associated IgG antibodies; moreover; GC levels in pat ients with EDTA-dependent PTCP were similar to control levels, thus ex cluding an increased platelet turnover. We conclude that antiplatelet antibodies directed against platelet cryptantigens are unlikely to hav e a major role in the increased removal of cells from circulation.