Background: Fast platelet function tests can identify weak clopidogrel responders, but data on variability over time in clopidogrel responsiveness in several clinical settings are lacking. We wanted to explore long-term variability of multiple electrode aggregometry (MEA) measurements and the agreement between MEA and light transmission aggregometry (LTA) in patients with non-ST elevation myocardial infarction (NSTEMI) treated with aspirin and clopidogrel.
Methods: Parallel MEA and LTA were performed at baseline and after 6 and 12 weeks in 31 patients treated with percutaneous coronary intervention after NSTEMI. Adenosine diphosphate (ADP) concentrations 2 μM, 6.5 μM and 10 μM were used. Parallel testings in both arterial and venous blood were performed at baseline. MEA and LTA cut-off levels were applied to discriminate aggregation values suggesting presence or absence of high platelet reactivity (HPR).
Results: Arterial and venous MEA and LTA aggregation were similar. Within-subject variability in both MEA and LTA aggregation throughout the study was moderate. According to MEA, eight patients had HPR at baseline (MEA aggregation > 47 U). Defining > 47% as the LTA aggregation HPR cut-off level, the same number of patients (eight) had HPR according to LTA. Of the 93 MEA/LTA observations 81 (87.1%) gave the same HPR classification. MEA vs. LTA agreement at baseline was slightly inferior to that obtained after 12 weeks.
Conclusions: MEA and LTA aggregation in arterial and venous blood seem similar. Within-subject variability over time was moderate, and the agreement between LTA and MEA was good, and stable in most patients.