Introduction: Dependability of platelet response testing remains a common dilemma among Stroke physicians. Our study reviewed whether being antiplatelet sensitive or resistant resulted in differences in stroke severity using the NIHSS at the time of presentation to ED.

Methods: This study was a retrospective cross-sectional cohort study of all patients presenting with a new ischemic stroke between 1/2009-12/2011;a total 381patients were included.Study participants were analyzed in groups consisting of those sensitive, resistant and not treated with either clopidogrel or aspirin. The group being treated with both clopidogrel and aspirin was compared to those not being treated with any antiplatelet therapy. Categorical data was compared between groups using Chi-square or Fisher’s exact tests as appropriate. Continuous data for age and NIH stroke scale score were not normally distributed and were transformed into rank data (non-parametric). Rank of age and NIH Stroke Scale score were then compared between groups using either the Mann-Whitney U-test or the Kruskal-Wallis test to compare distributions of rank data and the Median Test to compare median values. Spearman correlations were then performed on rank of NIH Stroke Scale score data for all group comparisons displaying significant differences in distribution or medians of rank data to determine the direction and magnitude of the differences.

Results: The distribution of rank NIHSS scores significantly differed between those sensitive to clopidogrel versus those that were not (p=0.049).Patients on both aspirin and clopidogrel who were sensitive to both were compared to those that were not sensitive to either and those not treated with either aspirin or clopidogrel.A direct correlation was detected between increasing NIHSS score and antiplatelet resistance (p=0.014,correlation coef= 0.157).Differences in vascular territories effected is discussed.

Conclusions: Our study shows that clopidogrel sensitivity appears to result in a decreased stroke severity. Our study did not show a similar finding with aspirin.

Patient Care: Our study supports the evidence behind platelet response tests for clopidogrel however did not show any specificity of testing for aspirin sensitivity. This depicts the need for larger scale studies on these commonly used lab tests.

Learning Objectives: This retrospective study provides evidence that antiplatelet resistance to clopidogrel results in differences in stroke severity.

References: 1. Milionis H, Michel P. Acute ischemic cerebrovascular events on antiplatelet therapy: What is the optimal prevention strategy? Curr Pharm Des. 2012 Dec 26. [Epub ahead of print] 2. Zheng AS, Churilov L, Colley RE, Goh C, Davis SM, Yan B. Association of aspirin resistance with increased stroke severity and infarct size. JAMA Neurol. 2013 Feb 1;70(2):208-13. doi: 10.1001/jamaneurol.2013.601. 3. Kim JH, Kim YS, Sohn SI, Cho KH. Biochemical Aspirin Resistance Affect on Stroke Severity in Acute Stroke Patients Who Had Taken Aspirin.  J Korean Neurol Assoc. 2011 Nov;29(4):303-308.