الفهرس 
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Abstract
Aspirin is a well established medication in treatment and prevention of atherothrombotic disease. Despite aspirin treatment, a substantial number of patients experience recurrent ischemic episodes. These patients are clinically referred to as ‘aspirin resistant’ or aspirin non-responders. Although there are several laboratory tests used to measure the antiplatelet effects of aspirin, the results from these tests showed poor correlation The results from measurement of urinary 11-dehydrothromboxane B2 (dTXB2) has been shown to correlate with future cardiovascular events in patients at high vascular risk who were treated with aspirin.
The present study aimed to evaluate the use of quantitative measurement of urinary 11-dehydrothromboxane B2 (11dhTxB2) as an indicator for platelet unresponsiveness in patients receiving anti-platelet drugs for primary and secondary prevention of coronary and cerebral artery diseases.
To achieve this target, 20 patients who were receiving aspirin as primary prevention of thromboembolic events (group I) and 20 patients who were receiving aspirin as secondary prevention for thromboembolic events (group II) were included in the study. In addition, there were 20 age and sex matched healthy controls (group III). All participants were subjected to careful history taking, thorough clinical examination and laboratory investigations including CBC, lipid profile and urinary 11-dehydro-thromboxane B2 (11-dTxB2).
Comparison of the 11-dTxB2 levels among the studied groups had shown that the group I and II had significantly lower 11-dTxB2 levels when compared to the control group. However, no significant differences could be detected between group I and II.
In our study, it was found that at a cut-off of 1494.5 TXB2 had a sensitivity of 60.0 %, a specificity of 50.0 %, a positive predictive value of 55.6 %, a negative predictive value of 54.5 % and accuracy of 55.0 %.
In respect to the association between 11-dehydro TXB2 levels and the demographic characteristics, the current study showed a significant positive correlation between TXB2 and BMI in harmony with other studies. However, we didn’t find any associations between urinary TXB2 and each of sex or age.
Considering the association between TXB2 and lipid profile, our study detected significant positive correlation between TXB2 and triglycerides, cholesterol and LDL levels. In spite of the trend towards inverse relation between TXB2 and HDL, the relation lacks statistical significance.
As regard the relation between 11-dehydro thromboxane B2 and platelet count, our study detected a significantly higher platelet count among patients with low 11-dehydro thromboxane B2 compared to patients with high 11-dehydro thromboxane B2 level.
Regarding the association between TXB2 and cardiovascular risk factors as estimated by the Framingham risk score, high risk patients had significantly higher 11-dehydro thromboxane B2 levels when compared to intermediate risk patients.
from the above findings we concluded that quantitave measurement of 11-dehydro thromboxane B2 was an accessible, non invasive & quantitave laboratory test amenable to routine use for monitoring aspirin response or resistance in patients receiving prophylactic aspirin therapy.
Moreover the relatively low performance of the established cutoff was compensated by its strong relevant clinical implication with the widely used clinical scoring system; Framingham risk score.