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clinmed/2000080002v1 (August 29, 2000)
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Platelet tests in the prediction of myocardial infarction and ischaemic stroke: evidence from the Caerphilly prospective study

Peter C. Elwood, Andrew Beswick, Janet Pickering, Peter McCarron, John R. O'Brien, Serge Renaud, and Rod Flower

A platelet test which is predictive of myocardial infarction (MI) and/or stroke would enable the targeting of antiplatelet drugs on patients at highest risk. The predictive power of several platelet tests for myocardial infarction (MI) and for stroke was examined. The tests were: aggregation to adenosine di-phosphate (ADP) in platelet rich plasma (PRP); aggregation to ADP in whole blood measured by an impedance method, and a test of platelet aggregation induced in whole blood by high-shear flow. Design: Prospective: base-line platelet tests were related to incident myocardial infarction (MI) and stroke events. Setting: The Caerphilly Cohort Study of Heart Disease, Stroke and Cognitive Decline. Subjects: Around 2,000 men aged 50 to 69 years, representing almost 90% of men in the cohort. Outcome measures: Around 200 MIs and 100 ischaemic strokes occurred during the following ten years. Results: Neither primary nor secondary aggregation in PRP was predictive of MI. The fifth of men in whom the primary response to ADP was least, showed the highest risk of a subsequent stroke (RO 1.64; 95% CI 1.12 to 2.43). Aggregation in whole blood was not predictive of MI but again the fifth of men with the least platelet response showed the highest stroke incidence (RO 1.79; 95% CI 1.06 to 3.00). Retention of platelets in the high-shear test was not predictive of either event. Conclusions: None of three platelet tests was found to be predictive of MI. Two tests of aggregation to ADP predicted stroke, but in a way opposite to that expected.