Inhibition of platelet aggregation by abciximab but not by aspirin can be detected by a new point-of-care test, the hemostatus

We have investigated the type of platelet defect that can be detected with the Hemostatus test performed with the Hepcon/HMS instrument (Medtronic) de signed to investigate platelet function during and after surgery. This assa y is based on the comparison of the activated clotting time of whole blood measured in cartridges containing kaolin or kaolin and platelet-activating factor in different concentrations. Addition of platelet-activating factor shortened the blood activated clotting time when the platelet counts were n ormal. However, when platelet counts were below 70000/mu L, the activated c lotting time was prolonged in all channels including those without platelet -activating factor showing the influence of platelets in the formation of t he clot under the conditions tested. Inhibition of platelet aggregation wit h c7E3 (abciximab, ReoPro) also induced a much-prolonged activated clotting time, and a similar finding was seen with blood from a patient with Glanzm ann's thrombasthenia confirming the need for platelet aggregation and/or th e glycoprotein (GP) Ilb-IIIa complex. In contrast, the interaction of GP Ib with von Willebrand Factor was not of major importance, since inhibition o f this interaction with the anti-GP Ib murine monoclonal antibody, ALMA-12, did not modify the activated clotting time. Furthermore, the activated clo tting time measured for patients with an acquired defect in von Willebrand Factor activity were unchanged. Finally, inhibition of thromboxane A2 forma tion by aspirin did not influence the results of this test. Globally, the H emostatus test was able to detect major abnormalities of GP IIb-IIIa functi on in the presence or absence of platelet-activating factor. (C) 1999 Elsev ier Science Ltd, All rights reserved.