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Introduction: Cerebral microembolic signals (MES) predict increased stroke risk in carotid stenosis however micro-emboli negative symptomatic patients also demonstrate increased risk compared to asymptomatic patients. Enhanced platelet activation may contribute to this risk disparity.Methods: We performed a prospective, observational analytical study assessing platelet counts, platelet activation status, and the relationship between platelet activation and MES in asymptomatic versus symptomatic moderate (≥50-69%) or severe (≥70-99%) carotid stenosis. Full blood count measurements were performed, and whole-blood flow cytometry used to quantify platelet surface activation marker expression (CD62P and CD63) and circulating leucocyte-platelet complexes. Bilateral simultaneous Transcranial Doppler (TCD) ultrasound monitoring of the middle cerebral arteries was performed to classify patients’ MES status.Results: Complete TCD data from 28 asymptomatic patients were compared with 35 symptomatic patients in the ‘early phase’ (≤4 weeks) and 30 of these patients in the ‘late phase’ (≥3 months) after TIA/ischaemic stroke. The %MES positive patients were higher in early symptomatic (31.4%; P = 0.027), but not in late symptomatic (6.7%; P = 0.996) vs. asymptomatic patients (7.1%). There were no significant differences in platelet counts, mean platelet volume, %CD62P or %CD63 expression between early/late symptomatic and asymptomatic MES negative patients (P>0.05). There were however, a significantly higher %circulating lymphocyte-platelet complexes in early symptomatic vs. asymptomatic patients (2.7% vs. 2.17%;P=0.02)Discussion: Increased lymphocyte-platelet complex formation in recently symptomatic vs. asymptomatic MES-negative patients indicates enhanced platelet activation in this early symptomatic subgroup. Platelet biomarkers, in combination with TCD, have the potential to aid risk-stratification in carotid stenosis.