Point-of-Care Whole Blood Impedance Aggregometry Versus Classical Light Transmission Aggregometry for Detecting Aspirin and Clopidogrel: The Results of a Pilot Study

BACKGROUND: We determined whether whole blood impedance aggregometry using the Multiplate detects the effects of antiplatelet drugs as reliably as does classical light transmission aggregometry (LTA) or the platelet function analyzer PFA-100(R). METHODS: Multiplate (M) assays, measuring changes in electrical resistance as aggregation units over time (AU*min), and LTA assays induced by collagen (COL), adenosine diphosphate (ADP) or arachidonic acid (AA) and PFA-100 testing, using epinephrine (PFA100-EPI) or ADP (PFA100-ADP) cartridges, were performed simultaneously using arterial blood samples obtained before induction of anesthesia in 70 consecutive patients scheduled for elective coronary artery bypass grafting. Patients in group A (n = 48) served as controls, patients in group B (n = 11) received aspirin 100 mg/d and those in group C (n = 11) aspirin 100 mg/d and clopidogrel 75 mg/d until the day before surgery. RESULTS: In controls the median (1st, 3rd quartiles) change in impedance AU*min for M-COL (374 [231-469]) was significantly greater than in patients receiving aspirin (164 [86-211], P = 0.0009) or receiving aspirin and clopidogrel (118 [101-244], P = 0.004). M-ADP values in controls were 258 (158-389), in patients receiving aspirin 261 (159-393), and in patients receiving aspirin and clopidogrel 88 (48-231, P = 0.054). M-AA values were significantly lower in patients receiving aspirin alone (45 [28-60], P = 0.0004) or aspirin and clopidogrel (44 [26-221], P = 0.008) than in controls (200 [86-345]). The areas under the receiver operating characteristic curves indicating the ability to discriminate patients taking aspirin from those not taking aspirin were comparable for COL and AA assays using whole blood impedance aggregometry or classical LTA (M-COL 0.84 [P = 0.001], LTA-COL 0.85 [P = < .001], M-AA 0.84 [P = < .001] and LTA-AA 0.87 [P = < .001]), but only 0.74 for PFA-100-EPI (P = 0.03). Similarly, for discrimination of patients not taking antiplatelet drugs from patients taking clopidogrel and aspirin the areas under the receiver operating characteristic curve were also comparable for both aggregometry methods M-COL 0.77 (P = 0.006), LTA-COL 0.78 (P = 0.004), M-ADP 0.74 (P = 0.015), LTA-ADP 0.73 (P = 0.018). CONCLUSION: Results achieved with the bedside Multiplate assays were not different than those obtained with classical aggregometry for detecting the effects of aspirin and clopidogrel in preoperative patients scheduled for elective cardiac surgery.