Objective      To determine the levels of platelet specific antigens and platelet-derived microparticle (PMPs) by flow cytometry (FCM) in hemophlia A patients

and analyze their clinical significances in the phenotype heterogeneity of the patients with severe hemophlia A.       Methods      Thirty-one patients with severe hemophlia A (aged from 18 to 33

median 23.5)  were enrolled in this study. They were 10 with mild type (annualized bleed rates 6) and 21 with moderate and severe type (annualized bleed rates ≥24). Another 17 healthy male volunteers served as normal controls. Their supernatant plasma samples were measured for baseline PMPs count

with phycoerythrin (PE)-conjugated monoclonal antibodies CD41. Fluorescent microspheres of 1.0 μm and standard fluorescent microbeads (0 to 1.0 μm) in diameter were used to set the microparticle gate

and the antibodies of CD41a-APC

CD42b-PE

CD61-FITC

CD62P-PE

and CD63-PE specific to platelets derived from platelets were employed to analyze the expression of corresponding platelet activating antigens by flow cytometry.       Results      The expression percentage of CD62P and CD63 was obviously higher in the mild type than the sever type patients (mean±SD: 49±11.81 vs 36.2±9.27

P=0.040 8）;（mean±SD: 51.15±14.3 vs 34.82±7.13

P=0.004 4) and a higher mean level of PMPs counts in mild type patients compared to severe type (mean±SD: 2.06±1.33 vs 0.95±0.64

P=0.02).       Conclusion      Platelet activating capacity and PMPs exert certain effect on clinical phenotypes of hemophlia A. The mild patients have stronger platelet activating capacity and higher PMPs count than the severe ones.