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.