Background: Diabetic patients have a tendency for higher post-treatment platelet reactivity (HPPR) to conventional antiplatelet therapy. Incomplete platelet inhibition before percutaneous coronary intervention (PCI) is associated with periprocedural myocardial injury. We aimed to test whether point-of-care platelet assay-guided decision on the antiplatelet therapy is beneficial to reduce myocardial injury during PCI in diabetic patients. Methods: Study flow is summarized in the figure. After 300mg loading of aspirin and clopidogrel to diabetic patients one day before the procedure, VerifyNow P2Y12 assay was performed just before the beginning of PCI. Patients were assigned to three groups according to PRU level. While bolus of 140IU/kg heparin was given to both control groups, test group received 70IU/kg heparin and loading dose of 0.25mg/kg abciximab before PCI. Clinically relevant periprocedural infarction was defined as any elevation of more than 3 times of upper normal limit in either of CK-MB or cTnI at the time of post-PCI 8, 16, and 24 hours. Clinical events such as bleeding were checked up to 1 month follow-up. Results: From June 2009 to July 2010, 64 diabetic patients were prospectively assigned to 3 study groups (28 patients in test group, 23 and 13 for control group 1 and 2). Clinical and procedural characteristics were comparable across study groups, and periprocedural infarction was present in 19 patients in test group, 13 and 7 in control group 1 and 2 (67.9%, 56.5% and 53.8% respectively, p=0.669) Only test group suffered 4 minor bleeding events such as hematoma (14.3%). No other adverse events were reported during the follow-up. Conclusion: Though small number of patients was assessed in this interim analysis, more than 75% of diabetic patients showed HPPR (PRU>270) even after the loading of dual antiplatelet agents. In addition, the incidence of periprocedural myocardial infarction was very frequent and this was not improved by additional platelet inhibition in spite of tailored approach with point-of-care assay.