Platelet Mapping Assay Interference Due to Platelet Activation in Heparinized Samples

OBJECTIVES: Thromboelastography Platelet Mapping (TEGPM) is an assay designed to detect platelet inhibition due to aspirin or clopidogrel-like drugs. The purpose of this study was to evaluate potential causes of error in the design or operation of the assay. METHODS: We evaluated percent inhibition of platelets due to aspirin or clopidogrel using TEGPM, which measures clot viscoelastic maximum amplitude (MA) after activation with adenosine diphosphate (ADP) or arachidonic acid (AA) and subtraction of MA due to fibrin (MAFibrin). RESULTS: MAFibrin measured in heparinized blood showed an unstable increasing pattern in 28% of samples (16 of 58). The platelet aggregation inhibitor eptifibatide corrected increasing MAFibrin in 14 of 16 cases, while the thrombin inhibitor argatroban corrected increasing MAFibrin in six of 16 cases, suggesting that unanticipated platelet activation/ aggregation was a more important cause of unstable rising MAFibrin than uninhibited thrombin. The unstable increased MAFibrin falsely increased percent ADP inhibition on average from 19% to 38% and percent AA inhibition from 29% to 58%. Heparinized samples showed platelet clumping and had procoagulant platelet microvesicle levels double those in citrate anticoagulant. CONCLUSIONS: Unanticipated platelet activation/aggregation occurring in the heparinized TEGPM samples lead to erroneous percent inhibition results.