Clopidogrel response: head-to-head comparison of different platelet assays to identify clopidogrel non responder patients after coronary stenting.

OBJECTIVES

We investigated the agreement between different platelet tests to identify clopidogrel non response.

BACKGROUND

Biological definition of clopidogrel non response remains controversial. Different platelet tests have been linked with recurrent ischemic events and proposed for daily practice.

METHODS

We prospectively investigated the agreement of platelet tests to isolate clopidogrel non response in patients receiving high 150 mg clopidogrel maintenance dose after coronary stenting. Clopidogrel response was assessed with ADP-induced aggregation (ADP-Ag) (non response if >70%), Platelet reactivity index VASP (PRI VASP) (non response if >50%) and Verify Now Point-of-care assay (VN) (non response if PRU > 240 AU).

RESULTS

Seventy consecutive patients were included. The rates of non-responders were respectively: 13% (n = 9) with the ADP-Ag, 39% (n = 27) with the PRI VASP and 33% (n = 23) with the VN. We observed significant correlation between different platelet tests assessing clopidogrel response: r = 0.55 (p < 0.0001) for ADP-Ag and PRI VASP, r = 0.64 (p < 0.0001) for ADP-Ag and VN and r = 0.59 (p < 0.0001) for PRI VASP and VN. However, using the most common thresholds, the agreement between the difference tests was poor: 0.35 for ADP-Ag and PRI VASP, 0.36 for ADP-Ag and VN and 0.46 for PRI VASP and VN.

CONCLUSION

This study showed that assessment of platelet function inhibition by clopidogrel is highly test-specific. Indeed, our results demonstrated a poor agreement between different platelet assays and suggested that identification of clopidogrel non responders is test-dependent.