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Background Routine platelet function testing in patients undergoing flow diversion remains controversial, with widespread use but inconsistent adoption as standard of care, particularly in publicly funded healthcare systems such as Canada. This study aimed to determine whether nonresponsiveness to clopidogrel or ticagrelor, measured by whole blood impedance aggregometry, was associated with symptomatic thromboembolic events following flow diversion, and whether ticagrelor use was associated with lower thromboembolic risk compared to clopidogrel.Methods A prospective cohort study was conducted at Foothills Medical Centre (Calgary, Canada) between August 2019 and April 2021, and between August 2024 to November 2025. Consecutive patients undergoing flow diversion while receiving dual antiplatelet therapy were enrolled. Platelet responsiveness was assessed using whole blood impedance aggregometry. The primary outcome was symptomatic thromboembolic complication within 90 days. Treating physicians were blinded to aggregometry results and antiplatelet selection was not based on platelet function testing. Ticagrelor use reflected institutional practice patterns during later study periods rather than individualized adjustment based on aggregometry result. Multivariable Firth logistic regression was used to evaluate associations with thromboembolic complications after adjustment for relevant covariates.Results Fifty-nine patients underwent flow diversion (83.1% female, mean age 55.0 ± 12.8 years). Thromboembolic complications occurred in 7/59 patients (11.9%). Patients classified as nonresponders (maximal ADP impedance >/=5) had significantly higher thromboembolic events rates compared to responders (35.7% vs 4.4%; Fisher’s exact OR 11.24, p=0.006). In univariate Firth logistic regression, nonresponder status was associated with increased odds of thromboembolic complications (OR 10.07, p=0.004). After adjustment for age and platelet count, which demonstrated associations with thromboembolic complications on univariate analyses, nonresponder status remained independently associated with thromboembolic complications (OR 5.73, p=0.046). Ticagrelor was used in 29/59 patients (49.2%), while 30/59 received clopidogrel. Thromboembolic complications occurred in 3/29 ticagrelor-treated patients (10.3%) and 4/30 clopidogrel-treated patients (13.3%) (p=1.000).Conclusions Nonresponsiveness to clopidogrel or ticagrelor, as measured by whole blood impedance aggregometry, was associated with increased thromboembolic risk following flow diversion. Ticagrelor use was not associated with reduced thromboembolic complications in this cohort. These findings support platelet function testing as a potential tool for identifying patients at elevated thromboembolic risk following flow diversion.Disclosures C. Veilleux: None. S. Muram: None. A. Kulamurugan: None. B. Karmur: None. T. Wong: None. E. Hu: None. P. Croney: None. A. Mitha: None.