Comparing light transmission aggregometry and PFA100 for monitoring antiplatelet therapy in patients with coronary heart disease

Many patients undergoing antiplatelet therapy continue to experience thrombotic events and failure of therapy leading to so-called ‘resistance’ to antiplatelet therapy. Recently, there has been an increasing focus on in vitro laboratory monitoring of platelet functions, which has the promise of identifying these patients. This study aimed to document the prevalence of laboratory evidence of resistance to aspirin and clopidogrel therapy in Saudi patients with stable coronary heart disease (CHD). Light transmission aggregometry in platelet-rich plasma was performed in response to adenosine diphosphate (ADP), arachidonic acid (AA), collagen and adrenaline. In addition, a platelet function analyser (PFA100) was employed using both collagen/ADP and collagen/epinephrine cartridges. Light transmission aggregometry (LTA) identified the resistance to aspirin and clopidogrel therapy, according to the persistence of the aggregation response to AA aggregation, to be 13% and 26%, respectively. By PFA100 testing, closure times within the limits of laboratory reference values indicated residual platelet reactivity, and the prevalence of resistance to anti-platelet therapy was reported to be 33% for collagen/ADP cartridges and 30.7% for collagen/epinephrine. A concordance between LTA and PFA100 CT was noted in only 22.6% of patients. This study showed a wide prevalence of on-treatment platelet reactivity in patients with CHD on dual platelet therapy (aspirin and clopidogrel). In addition, the global whole blood test of platelet function by PFA100 estimated a much higher prevalence of resistance than LTA when compared to the gold standard and more specific LTA analysis.