Use of mean platelet component to measure platelet activation on the ADVIA120 haematology system

Platelet activation results in changes in a number of cell surface molecule s including an increase in P-Selectin (CD62P) that may be rapidly and conve niently measured by immunofluorescent flow cytometry. The ADVIA 120 (Bayer) is a new system that facilitates more accurate measurement of platelet vol ume and in addition provides an approximate measure of the mean refractive index (RI) of the platelets reported as mean platelet component (MPC) conce ntration. We were interested to determine whether changes in MPC might refl ect changes in platelet activation status. To investigate this, the platele t CD62P expression, determined by flow cytometry, and change in MPC, measur ed an the ADVIA 120 system, was first examined in vitro after stimulation o f EDTA anticoagulated whole blood with submaximal concentrations of bovine thrombin in the presence or absence of the thromboxane synthase inhibitor, Ridogrel. Thrombin produced a dose-dependent increase in platelet CD62P exp ression and a decrease in MPC that could be inhibited by Ridogrel at physio logical concentrations. In the second set of experiments, blood from 20 nor mal controls was collected into both EDTA and sodium citrate (SC) anticoagu lants. Within 30 min of venesection and again at 3 h post-venesection after storage at room temperature, the platelet MPC and CD62P expression were de termined. Platelets in all samples with both anticoagulants showed very low levels of CD62P expression when first analysed. At 3 h there was a small i ncrease in CD62P expression on platelets in whole blood anticoagulated with SC, but a significant (P < 0.001) increase was observed on platelets anti- coagulated with EDTA. A negative correlation was found between the change i n MPC of the platelets and the increase in the mean fluorescence intensity (MFI) (r = -0.69, P < 0.001, n = 20) and the percentage (r = -0.72, P < 0.0 01, n = 20) of CD62P positive platelets at 3 h in blood anticoagulated with EDTA. We conclude that a reduction in MPC as measured by the ADVIA 120 may be used to detect anticoagulant induced, as well as thrombin stimulated, i n vitro platelet activation in blood anticoagulated with EDTA. Further, we conclude that platelet activation is negligible for up to 3 h in sodium cit rate anticoagulated whole blood. (C) 1999 Wiley-Liss, Inc.