Changes in response to clopidogrel therapy in patients after percutaneous coronary interventions as assessed by different platelet function tests

INTRODUCTION Recently, the responder status to clopidogrel therapy has been observed to change over time.
OBJECTIVES The aim of the study was to investigate changes in the responder status to clopidogrel therapy over time with the use of 4 platelet function tests (light transmission aggregometry [LTA], multiple electrode aggregometry [MEA], vasodilator-stimulated phosphoprotein (VASP) phosphorylation, and INNOVANCE® PFA P2Y assays [PFA]) in patients after percutaneous coronary intervention (PCI). We also compared the results of these tests to determine the most reliable method.
PATIENTS AND METHODS The study included 35 patients after PCI, receiving acetylsalicylic acid (75 mg/d) and clopidogrel (75 mg/d). The control group included 50 healthy volunteers. Platelet function was measured at 3 different time points (4 ±2 days after PCI, and then after 6 and 12 weeks). 
RESULTS The responder status to clopidogrel changed in 5 patients (14%) as shown by MEA; in 7 patients (20%), by LTA and PFA; and in 13 patients (37%), by VASP. The Cohen’s κ coefficient showed a moderate or poor agreement between the tests. The strongest agreement was between MEA and PFA (80%; κ = 0.46, P = 0.003), PFA and LTA (82%; κ = 0.41, P = 0.004), and MEA and LTA (80%; κ = 0.36, P = 0.008). The κ coefficient for all comparisons with VASP was less than 0.30.
CONCLUSIONS Changes in the responder status over time are present for all platelet function tests, but a large discrepancy between the tests does not allow a careful assessment of this phenomenon. The tests showed only moderate agreement (in relation to one another and to time points), which significantly limits their interchangeable use in clinical practice.