The Cone-and-Plate(let) analyzer is not suitable to monitor clopidogrel therapy: A comparison with the flowcytometric VASP assay and optical aggregometry

Introduction

High on-clopidogrel platelet reactivity has been associated with an increased risk for atherothrombotic events. A new player on the horizon is the IMPACT-R ADP-test using ADP pre-stimulation. We here report the results of a thorough evaluation of this new device.

Materials and methods

The IMPACT-R ADP-test was evaluated in different categories of subjects. First, normal range values were determined in healthy subjects (n = 46). Second, the effect of 600 mg of clopidogrel was evaluated with the IMPACT-R ADP-test and two other well-validated methods (flowcytometric VASP-analysis and optical aggregometry) in 21 patients. Third, a head-to-head comparison between the IMPACT-R ADP-test and optical aggregometry was performed in a large cohort of patients on dual antiplatelet therapy.

Results

The results of the IMPACT-R ADP-test were highly variable throughout healthy subjects. The administration of a high clopidogrel loading dose resulted in a small but significant increase in surface coverage but 61.9% of the patients were still identified as clopidogrel nonresponder. In contrast, optical aggregometry and VASP-analysis identified 24% and 33% of these patients as a clopidogrel nonresponder, respectively. Head-to-head comparison with optical aggregometry in 451 patients showed only a modest correlation between both methods (r ∼ 0.20, p < 0.0001).

Conclusions

The IMPACT-R ADP-test is relatively insensitive to the effects of clopidogrel and cannot substitute for methods such as flowcytometric VASP-analysis and optical aggregometry. Further studies are required to establish the clinical usefulness of IMPACT-R ADP-test to accurately predict the occurrence of major adverse cardiovascular events in patients with high on-clopidogrel platelet reactivity before it can be implemented in clinical practice.