Rapid Platelet Function Assay Research Articles

Current methods of measuring platelet activity: pros and cons.

: Platelets play a pivotal role in controlling hemorrhaging from vessels of the human body. The impairment of platelets may lead to the development of bleeding manifestations. Unraveling the precise defects of platelets by means of suitable laboratory methods paves the way for the effective control and management of platelet disorders. Choosing the most appropriate approach for the detection of platelet disorders may be difficult for a researcher or clinical internist when faced with ordering a platelet-function test. The aim of the current study was to provide a user-friendly overview of the advantages and disadvantages of the available detection systems. To reach this goal, 11 commonly used methods of studying platelet activity were evaluated and compared in detail. A literature search, with no time or language limitations, was conducted in Google Scholar and Medline. All publications published before June 2019 were analyzed. The following laboratory methods were compared: number and size of platelets, bleeding time, clot retraction time, platelet function assay 100 & 200, Rapid platelet function assay, flow cytometry, light transmission aggregometry, multiple electrode aggregometry, 96-well plate aggregometry, cone and plate(let) analyzer (Impact-R), and Plateletworks (single platelet counting system). This article provides the reader with a rapid comparison of the different systems used to study platelets activities.

Safety and efficacy of antiplatelet response assay and drug adjustment in coil embolization: a propensity score analysis.

The purpose of this study was to explore the safety and efficacy of an antiplatelet response assay and drug adjustment to prevent delayed thromboembolic events after stent-assisted coil embolization. A total of 370 patients were enrolled in this study between December 2005 and July 2014. Of these, 124 patients were placed into the drug resistance test (DRT) group with drug adjustment according to response to an antiplatelet agent, and 246 patients comprised the control group with a standard antiplatelet regimen. The response to the antiplatelet agent was evaluated with the VerifyNow Rapid Platelet Function Assay. Propensity score matching analysis was performed with one-to-multiple matching. Among 370 patients, delayed thromboembolic events occurred in 28 (7.6%) patients including 25 (10.2%) in the control group and three (2.4%) in the DRT group. Antiplatelet response test (p=0.012), diabetes mellitus (DM) (p=0.014), and hypertension (HTN) (p<0.001) were associated with delayed infarction in multivariate analysis. In propensity score matching analysis, 331 patients were matched (control group (n=229) vs. DRT group (n=103)), and antiplatelet response (hazard ratio 0.247, 95% confidence interval 0.070-0.868, p=0.029) was correlated with delayed infarction. Conversely, the two groups were not significantly different with regard to total (p=0.368) or major hemorrhagic complications (p=0.108). Antiplatelet drug adjustment according to the results of an antiplatelet response assay might be associated with a decreased risk of delayed thromboembolic infarction compared with the standard antiplatelet regimen.

Platelet activation, coagulation activation and C‐reactive protein in simultaneous samples from the vascular access and peripheral veins of haemodialysis patients

Most studies of haemodialysis (HD) patients compare venous blood samples from controls with samples from the vascular access (VA) of HD patients. We hypothesised that VA samples may be more prothrombotic compared with venous samples. Samples were taken simultaneously from the VA and the contralateral antecubital vein, from 26 patients immediately before HD. Platelet function was assessed by (1) flow cytometric measurement of P-selectin expression and fibrinogen binding (±ADP) and 2) Ultegra rapid platelet function assay. Plasma soluble P-selectin, von Willebrand factor antigen, high sensitivity C-reactive Protein (hs-CRP), thrombin-antithrombin III complex and D-dimer measured by ELISA. Thrombin receptor activating peptide-induced platelet aggregation (P < 0.001) and hs-CRP (P < 0.001) were higher in VA compared with venous samples. Unstimulated platelet fibrinogen binding (P = 0.016) and ADP-stimulated P-selectin expression (P = 0.008) were lower in VA compared with venous samples. The significant difference in hsCRP persisted when patients taking and not taking antiplatelet therapy were analysed separately, but platelet activation remained significantly different only in the nonantiplatelet group. There are statistically significant differences between sampling sites, although samples from the VA do not appear to be more pro-thrombotic. Future studies comparing HD patients with controls should ensure uniformity of sampling sites to prevent inaccurate conclusions being drawn.

Prothrombotic Changes in Platelet, Endothelial and Coagulation Function following Hemodialysis

Patients on hemodialysis (HD) have an increased risk of thrombotic events, including myocardial infarction and vascular access thrombosis. The study hypothesis is that a single session of dialysis leads to platelet, endothelial and coagulation activation. Our aim is to determine the effect of a single HD session on prothrombotic vascular biomarkers before and after a single session of hemodialysis. Blood samples were taken from the vascular access of 55 patients immediately before and after a hemodialysis session. Platelet function was assessed by (1) flow cytometric measurement of P-selectin expression and fibrinogen binding +/- ADP stimulation, (2) Ultegra rapid platelet function assay (RPFA) using the agonists thrombin receptor activating peptide (TRAP) and arachidonic acid (AA), (3) soluble P-selectin, and (4) soluble CD40L. Coagulation (thrombin-antithrombin III [TAT] and D-dimer), endothelial von Willebrand factor (vWF) and high sensitivity C-Reactive protein (hsCRP) were assessed by ELISA. Unfractionated heparin was given to all patients during dialysis and 30 patients (55%) were on antiplatelet agents. Post-hemodialysis there were significant increases in unstimulated platelet P-selectin (p=.037), stimulated P-selectin (p<.001), soluble P-selectin (p<.001) and soluble CD40L (p=.036). Stimulated platelet fibrinogen binding was increased post-hemodialysis (p<.001) but unstimulated fibrinogen binding was unchanged. TRAP- (p<.001] and AA-(p=.009) stimulated aggregation were reduced post-hemodialysis. There were increases post-hemodialysis in TAT (p<.001), D-dimer (p<.001), vWF (p<.001) and hsCRP (p=.011). This study has shown that despite heparin therapy, a single session of HD induced increases in platelet, endothelial, and coagulation activation. More effective medical strategies to reduce the prothrombotic state of patients on hemodialysis should be investigated.

DMSO inhibits human platelet activation through cyclooxygenase-1 inhibition. A novel agent for drug eluting stents?

Background: DMSO is routinely infused together with hematopoietic cells in patients undergoing myeloablative therapy and was recently found to inhibit smooth muscle cells proliferation and arterial thrombus formation in the mouse by preventing tissue factor (TF), a key activator of the coagulation cascade. This study was designed to investigate whether DMSO prevents platelet activation and thus, whether it may represent an interesting agent to be used on drug eluting stents. Methods and results: Human venous blood from healthy volunteers was collected in citrated tubes and platelet activation was studied by cone and platelet analyzer (CPA) and rapid-platelet-function-assay (RPFA). CPA analysis showed that DMSO-treated platelets exhibit a lower adherence in response to shear stress (−15.54 ± 0.9427%, n = 5, P < 0.0001 versus control). Additionally, aggregometry studies revealed that DMSO-treated, arachidonate-stimulated platelets had an increased lag phase (18.0% ± 4.031, n = 9, P = 0.0004 versus control) as well as a decreased maximal aggregation (−6.388 ± 2.212%, n = 6, P = 0.0162 versus control). Inhibitory action of DMSO could be rescued by exogenous thromboxane A2 and was mediated, at least in part, by COX-1 inhibition. Conclusions: Clinically relevant concentrations of DMSO impair platelet activation by a thromboxane A2-dependent, COX-1-mediated effect. This finding may be crucial for the previously reported anti-thrombotic property displayed by DMSO. Our findings support a role for DMSO as a novel drug to prevent not only proliferation, but also thrombotic complications of drug eluting stents.

Assessment of the bioequivalence of brand and biogeneric formulations of abciximab for the treatment of acute coronary syndrome: A prospective, open-label, randomized, controlled study in Korean patients

Background: Abciximab has been found to reduce major adverse cardiovascular events in patients with acute coronary syndrome (ACS). A previous study reported on the tolerability of biogeneric abciximab in patients with ACS. This formulation has been approved by the Korea Food and Drug Administration and is currently being marketed. Its ex vivo antiplate-let effect, however, has not been compared with that of branded abciximab. Objective: The purpose of the present study was to compare ex vivo antiplatelet activity, angiographic outcome, and bleeding complications between biogeneric and branded abciximab. Methods: This prospective, open-label, randomized, controlled study was conducted in Korea. Patients with ACS who underwent percutaneous coronary intervention (PCI) were randomized to receive bioge-neric abciximab or branded abciximab. All patients received intracoronary unfractionated heparin 70 IU/kg and either biogeneric or branded abciximab 0.25 mg/kg IV bolus ~10 minutes before undergoing PCI, followed by a 0.125 μg/kg/min 12-hour infusion of the same formulation. The antiplatelet effect of both drugs was assessed at 3 time points (at baseline, and 10 minutes and 24 hours after the end of the bolus infusion) using a validated rapid platelet-function assay. Results: In total, 37 patients (30 men and 7 women; 19 receiving biogeneric abciximab and 18 receiving branded abciximab) were included. Patient demographics did not differ significantly between the 2 groups (16 men [84.2%] and 3 women [15.8%] in the biogeneric group vs 14 men [77.8%] and 4 women [22.2%] in the branded group; mean [SD] age, 65 [11] vs 60 [10] years; weight, 64.6 [8.7] vs 67.9 [10.1] kg, respectively). The bolus and the continuous infusion of the biogeneric and branded formulations achieved similar levels of platelet inhibition, with a mean (SD) inhibition of platelet aggregation >90% at 10 minutes after the end of the bolus infusion (94.7% [8.2%] vs 92.6% [16.9%], respectively; P = NS) and >65% at 24 hours (68.1% [9.8%] vs 70.9% [9.7%]; P = NS) compared with baseline. One thrombolysis in myocardial infarction major bleeding complication (retro-peritoneal hemorrhage) was reported in a patient who received biogeneric abciximab. Conclusion: There were no statistically significant differences in the antiplatelet effects of these 2 formulations in this small, selected population of Korean patients with ACS.

Pro-thrombotic changes in platelet, endothelial and coagulation function following haemodialysis

Purpose: Patients on hemodialysis (HD) have an increased risk of thrombotic events, including myocardial infarction and vascular access thrombosis. The study hypothesis is that a single session of dialysis leads to platelet, endothelial & coagulation activation. Our aim is to determine the effect of a single HD session on prothrombotic vascular biomarkers before and after a single session of hemodialysis. Methods: Blood samples were taken from the vascular access of 55 patients immediately before and after a hemodialysis session. Platelet function was assessed by (1) flow cytometric measurement of P-selectin expression and fibrinogen binding ± ADP stimulation, (2) Ultegra rapid platelet function assay (RPFA) using the agonists thrombin receptor activating peptide (TRAP) and arachidonic acid (AA), (3) soluble P-selectin, and (4) soluble CD40L. Coagulation (thrombin-antithrombin III [TAT] and D-dimer), endothelial von Willebrand factor (vWF) and high sensitivity C-Reactive protein (hsCRP) were assessed by ELISA. Results: Unfractionated heparin was given to all patients during dialysis and 30 patients (55%) were on antiplatelet agents. Post-hemodialysis there were significant increases in unstimulated platelet P-selectin (p=.037), stimulated P-selectin (p<.001), soluble P-selectin (p<.001) and soluble CD40L (p=.036). Stimulated platelet fibrinogen binding was increased post-hemodialysis (p<.001) but unstimulated fibrinogen binding was unchanged. TRAP- (p<.001) and AA-(p=.009) stimulated aggregation were reduced post-hemodialysis. There were increases post-hemodialysis in TAT (p<.001), D-dimer (p<.001), vWF (p<.001) and hsCRP (p=.011). Conclusion: This study has shown that despite heparin therapy, a single session of HD induced increases in platelet, endothelial, and coagulation activation. More effective medical strategies to reduce the prothrombotic state of patients on hemodialysis should be investigated.

CYP2C19*2 and *3 Polymorphisms Are Associated with High Post- Treatment Platelet Reactivity in Korean Patients with Acute Coronary Syndrome Undergoing Percutanous Coronary Intervention.

Background: Cytochrome P450 (CYP) 2C19 is an enzyme showing genetic polymorphism that may cause marked interindividual and interethnic variation in the metabolism and disposition of its substrates. CYP2C19*2 and CYP2C19*3 are the most common of CYP2C19 polymorphisms, and show phenotypic poor metabolism. Recent data have shown that the CYP2C19*2 loss-of-function allele is associated with a marked decrease in platelet response to clopidogrel in healthy controls and Caucasian patients with acute coronary syndrome. However, It is unknown whether CYP2C19 *3, which is frequently noted in Asian, is also associated with platelet response to clopidogrel. Therefore, this study was conducted to analyze the effect of CYP2C19 *2 and *3 polymorphisms on high post-treatment platelet reactivity (HPPR) on clopidogrel in Korean patients with acute coronary syndrome, as a representative of Asian populations.Methods: The study included 136 consecutive patients undergoing percutanous coronary intervention (PCI). Adenosine diphosphate (ADP)-induced platelet aggregation by light transmittance aggregometry (LTA) and the VerifyNow P2Y12 assay (Ultegra rapid platelet function assay; Accumetrics Inc., USA) were assessed after a loading dose and after the maintenance dose of clopidogrel before discharge. CYP2C19 genotype was analyzed by Snapshot method.Results: The genotypic distributions of CYP2C19*1/*1, *1/*2, *1/*3, *2/*2, and *2/*3 were 57 (41.9%), 47 (34.6%), 12 (8.8%), 14 (10.3%), 6 (4.4%), and 6(4.4%), respectively. The frequencies of CYP2C19 mutant alleles in Korean were higher than Caucasians. The CYP2C19*2 and CYP2C19*3 polymorphisms were significantly associated with persistent higher platelet aggregation by LTA, and lower inhibition of platelet reactivity by VerifyNow P2Y12 assay after clopidogrel than CYP2C19*1 genotype. The CYP2C19*2 and *3 alleles were more frequent in clopidogrel hyporesponsiveness, defined by persistent HPPR (5 uM ADP-induced platelet aggregation >50%; p = 0.01).Conclusions: This study suggests that the CYPC19*2 and *3 alleles influence clopidogrel hyporesponsiveness after clopidogrel in Asian patients with acute coronary syndromes undergoing PCI. These findings can have a significant impact on the future design of pharmacognetic antiaggregant strategies for acute coronary syndrome on antiplatelet treatment.

Clopidogrel and Aspirin in Cardiovascular Medicine: Responders or Not -- Current Best Available Evidence

Dual antiplatelet therapy represents an important advance for patients with established coronary artery disease. It is an important strategy for patients with acute coronary syndromes and those undergoing percutaneous transcatheter coronary interventions. Clopidogrel effectively inhibits ADP-induced platelet activation and aggregation by selectively and irreversibly blocking the P2Y(12) receptor on the platelet membrane. Aspirin works by irreversibly acetylating the cyclooxygenase (COX-1) enzyme, thus suppressing the production of thromboxane A(2) (TxA(2)) and inhibiting platelet activation and aggregation. Variable platelet response and potential resistance to therapy has emerged with aspirin and clopidogrel. The definitions of antiplatelet agents variability in responsiveness and nonresponsiveness are discussed. Clopidogrel and aspirin responsiveness as they are measured in the laboratory by various techniques (platelet aggregometry and point-of-care assays such as platelet function analyzer [PFA-100] and rapid platelet function assay [RPFA]) are evaluated. The mechanisms responsible for variations in responsiveness to antiplatelet agents such as clinical, cellular and genetic factors are defined. Aspirin and clopidogrel resistance are emerging clinical entities with potentially severe consequences such as myocardial infarction, stroke or death. The therapeutic interventions to deal with nonresponsiveness are reported, although specific recommendations are not clearly established. In the future, routine measurement of platelet function in patients with cardiovascular disease may become the standard of care. Personalized antithrombotic treatment strategies may be determined by ex-vivo measurements that identify critical pathways influencing thrombotic risk in the individual patient.

A pilot study of resistance to aspirin in stroke patients

Aspirin resistance has been shown to be a significant risk factor for recurrent cardiovascular ischaemic events. However, there are a lack of data correlating aspirin resistance and risk of cerebrovascular ischaemic events. This pilot study aimed to determine the prevalence of aspirin resistance in an Australian stroke population and to correlate aspirin resistance with an increased risk of ischaemic stroke. Fifty patients treated with aspirin for 2 years were tested for aspirin resistance using the Ultegra Rapid Platelet Function Assay (Accumetrics, San Diego, CA, USA) on admission to Royal Melbourne Hospital for ischaemic stroke. The 2-year history of ischaemic stroke and transient ischaemic attack (TIA) were assessed. Prevalence of aspirin resistance among our patients was 30%. Univariate analysis suggested a non-significant trend towards increased rate of previous ischaemic stroke or TIA and aspirin resistance (odds ratio, OR = 3.88; 95% confidence interval 0.54–29.87; p = 0.18). This study shows that aspirin resistance is prevalent within the Australian ischaemic stroke population.

Elevated Plasma Fibrinogen and Diabetes Mellitus Are Associated With Lower Inhibition of Platelet Reactivity With Clopidogrel

The goal of this study was to identify factors associated with lower platelet inhibition (PI) with clopidogrel in subjects with cardiovascular disease (CVD). A heterogeneous platelet reactivity response to clopidogrel exists, and the clinical or biochemical predictors of suboptimal PI with clopidogrel remain unclear. This study prospectively enrolled subjects with CVD requiring treatment with clopidogrel (75 mg daily for > or =7 days or 600-mg bolus > or =24 h before recruitment). A bedside rapid platelet function assay (VerifyNow, Acccumetrics, San Diego, California) to measure maximal and clopidogrel-mediated platelet reactivity was utilized, and factors associated with lower PI were identified. A heterogeneous, normally distributed PI (mean 40.8 +/- 26.2%) response to clopidogrel was observed in 157 subjects (age 67.2 +/- 12.2 years; 59.9% men). Multiple variable analysis of clinical and biochemical factors known to affect platelet reactivity revealed lower PI in patients with an elevated plasma fibrinogen level (> or =375 mg/dl), diabetes mellitus, and increased body mass index (BMI) (> or =25 kg/m(2)). On testing for interaction, elevated fibrinogen level was associated with diabetic status, resulting in lower PI in diabetic patients (23.9 +/- 3.9% vs. 45.1 +/- 4.5%, p < 0.001), but not nondiabetic patients (44.7 +/- 4.4% vs. 46.3 +/- 4.8%, p = 0.244). Increased BMI remained independently associated with lower PI after clopidogrel therapy regardless of diabetic status or fibrinogen level (36.8 +/- 9.0% vs. 49.0 +/- 7.0%, p < 0.001). Elevated plasma fibrinogen (> or =375 mg/dl) in the presence of diabetes mellitus and increased BMI (> or =25 kg/m(2)) are associated with lower PI with clopidogrel in patients with CVD.

Platelet activation increases with the severity of peripheral arterial disease: Implications for clinical management

Patients with peripheral arterial disease (PAD) have increased mortality from cardiovascular events compared with age and sex matched controls Platelets play a major role in atherosclerosis and thrombotic vascular events. Platelet reactivity is increased in patients with PAD compared with healthy controls. We aimed to determine the relationship, if any, between platelet activation and severity of disease. One hundred eighty-two patients with intermittent claudication (IC) or subcritical limb ischemia (SLI), defined as the presence of rest pain or ulceration, had the following investigations performed: platelet P-selectin expression and bound fibrinogen by flow cytometric analysis and platelet aggregation using the rapid platelet function assay with arachidonic acid (AA) and thrombin receptor activation peptide (TRAP) as agonists. Patients with SLI compared with IC had significantly enhanced ADP stimulated P-selectin expression (median 42.45% [inter-quartile range 33.32% to 58.5%] vs 35.2% [26.07% to 46.32%], P = .002) and bound fibrinogen (73.7% [54.3% to 83.2%] vs 63.7% [43.8% to 76.5%], P = .001). TRAP stimulated aggregation was higher (207 [153 to 238] PAU vs 183[155 to 199] PAU, P = .04) but AA mediated aggregation was not significantly different. An ankle-brachial pressure index (ABPI) of less than 0.6 was associated with increased ADP stimulated P-selectin and bound fibrinogen (P < .05). ABPI correlated inversely with ADP stimulated P-selectin expression (r = -0.228, P = .003), ADP stimulated fibrinogen binding (r = -0.156, P = .043) and TRAP stimulated aggregation (r = -0.179, P = .04). We have demonstrated for the first time that progression of severity of PAD is not only reflected by symptoms, signs, and ABPI but also by increased platelet activity as assessed by both flow cytometry and aggregation. As patients with more severe PAD have increased cardiovascular mortality, our findings suggest that new strategies for platelet inhibitory therapy are indicated in these patients.

Aspirin Resistance and Adverse Clinical Events in Patients with Coronary Artery Disease

Purpose We sought to determine the clinical significance of aspirin resistance measured by a point-of-care assay in stable patients with coronary artery disease (CAD). Methods We used the VerifyNow Aspirin (Accumetrics Inc, San Diego, Calif) to determine aspirin responsiveness of 468 stable CAD patients on aspirin 80 to 325 mg daily for ≥4 weeks. Aspirin resistance was defined as an Aspirin Reaction Unit ≥550. The primary outcome was the composite of cardiovascular death, myocardial infarction (MI), unstable angina requiring hospitalization, stroke, and transient ischemic attack. Results Aspirin resistance was noted in 128 (27.4%) patients. After a mean follow-up of 379 ± 200 days, patients with aspirin resistance were at increased risk of the composite outcome compared to patients who were aspirin-sensitive (15.6% vs 5.3%, hazard ratio [HR] 3.12, 95% confidence intervals [CI], 1.65-5.91, P < .001). Cox proportional hazard regression modeling identified aspirin resistance, diabetes, prior MI, and a low hemoglobin to be independently associated with major adverse long-term outcomes (HR for aspirin resistance 2.46, 95% CI, 1.27-4.76, P = .007). Conclusions Aspirin resistance, defined by an aggregation-based rapid platelet function assay, is associated with an increased risk of adverse clinical outcomes in stable patients with CAD.

Assessing aspirin responsiveness using the Verify Now Aspirin assay

We read with great interest the study of Dyskiewicz-Korpanty et al. recently published in Thrombosis Research [1]. They evaluate aspirin responsiveness in 50 healthy subjects taking 325 mg/d during 3 days using whole blood impedance platelet aggregation and the rapid platelet function assay Verify Now™ Aspirin (RPFA, Accumetrics, San Diego, USA). Arachidonic acid-induced whole blood platelet aggregation (AA-aggregation) showed a 100% inhibition by aspirin in all subjects while there was a more limited effect when collagen was used as the agonist.

Measuring Aspirin Resistance, Clopidogrel Responsiveness, and Postprocedural Markers of Myonecrosis in Patients Undergoing Percutaneous Coronary Intervention

Aspirin and clopidogrel are proven to prevent thromboembolic events during percutaneous coronary intervention (PCI). Enzyme release of creatine kinase-MB (CK-MB) enzyme during PCI has been associated with an increased risk of future adverse cardiac events. This study examined the correlation between measurements of aspirin resistance and the level of inhibition of the thienopyridine-specific P2Y12 platelet receptor and CK-MB release after PCI. We prospectively studied 330 patients with elective PCI treated with drug-eluting stents. Patients were pretreated with aspirin and clopidogrel. Patients with positive CK-MB or acute coronary syndrome and those on glycoprotein IIb/IIIa inhibitors were excluded. Serum assays of aspirin resistance (Ultegra Rapid Platelet Function Assay-ASA, Accumetrics) and clopidogrel resistance (Rapid Platelet Function Assay P2Y12, Accumetrics) were performed before PCI. Serum troponinI and CK-MB levels were measured at 8, 16, and 24 hours after PCI. Aspirin resistance unit (ARU) measurement > or =550 was detected in 12 patients (3.7%). Mean platelet reactivity unit (PRU; measurement of inhibition of P2Y12 activity) was 192.2 +/- 95.4 (lower PRU, more inhibition of P2Y12 receptor). There was no correlation between level of ARU or PRU and troponin I or CK-MB release after PCI at any time point. Only multivessel coronary disease was found to be a predictor of any increase in CK-MB in a multivariate analysis (odds ratio 2.2, 95% confidence interval 1.4 to 3.3, p = 0.0003). A positive correlation was found between levels of ARU and PRU. Target vessel revascularization/major adverse cardiac event rate at 6 months was 8.2% with no correlation between ARU or PRU and release of cardiac enzymes or occurrence of adverse cardiac events. In conclusion, this study does not support routine measurements of aspirin and clopidogrel resistance in stable patients undergoing PCI.

Comparison of a rapid platelet function assay – Verify Now™ Aspirin – with whole blood impedance aggregometry for the detection of aspirin resistance

The reported incidence of aspirin resistance or non-responsiveness ranges between 5 and 30% [1]. There is neither a uniformly accepted definition of aspirin resistance nor an established standard method to assess aspirin non-responsiveness in the laboratory. The PFA-100™ has been most often used to assess aspirin effect. Aspirin non-responsiveness by the PFA-100™ is defined as an absence of a prolongation of the Collagen–Epinephrine cartridge closure time [2]. The second most widely used method is Born's optical platelet aggregometry, a labor intensive, time-consuming method that requires technical expertise.

Association Between Level of Platelet Inhibition After Early Use of Abciximab and Myocardial Reperfusion in ST-Elevation Acute Myocardial Infarction Treated by Primary Percutaneous Coronary Intervention

The interindividual response to antiplatelet treatment is considerable, with the magnitude of response often related to the appearance of clinical events after elective percutaneous coronary intervention (PCI). We investigated whether platelet aggregation inhibition (PAI) by early administration of abciximab would affect myocardial reperfusion outcomes observed after PCI in patients with acute ST-elevation myocardial infarction (STEMI). Consecutive patients with STEMI who were treated with PCI in our center were recruited (n = 56). Successful reperfusion was defined as a final Thrombolysis In Myocardial Infarction grade 3 flow, myocardial blush grade 2 or 3, and ST-segment resolution >50%. PAI grade was determined with the Ultegra Rapid Platelet Function Assay. Successful reperfusion criteria were observed in 34 patients (61%). There were 6 patients (11%) with a PAI value <80% and 34 (61%) with a PAI value > or =95%. Eight patients (36%) of those whose PAI was <95% had all the indicators of successful reperfusion compared with 26 patients (77%) whose PAI was > or =95% (p = 0.005). After adjusting for other variables (time from symptom onset to balloon, which was independently associated with myocardial reperfusion), the relation remained significant (p = 0.006). In conclusion, in patients with STEMI that was treated with direct PCI, higher platelet inhibition responses with early administration of abciximab were associated with better myocardial reperfusion outcomes.

Variability in Extent of Platelet Function Inhibition After Administration of Optimal Dose of Glycoprotein IIb/IIIa Receptor Blockers in Patients Undergoing a High-Risk Percutaneous Coronary Intervention

The Ultegra Rapid Platelet Function Assay was used to measure the inhibition of platelet aggregation at baseline and 10 minutes and 8 hours after starting therapy in 114 patients undergoing high-risk percutaneous coronary intervention with the planned use of a glycoprotein IIb/IIIa inhibitor. The abciximab-treated patients received a 0.25 mg/kg bolus, followed by a 0.125 microg/kg/min infusion for 12 hours; the eptifibatide-treated patients received 2 boluses of 180 microg/kg administered 10 minutes apart, followed by a 2 microg/kg/min infusion for 24 hours; the tirofiban-treated patients received a 25 microg/kg bolus, followed by a 0.15 microg/kg/min infusion for 18 hours. Ten minutes after starting therapy, the mean level of platelet inhibition was 86 +/- 9% for abciximab, 92 +/- 6% for eptifibatide, and 95 +/- 5% for tirofiban (p <0.001); > or =95% platelet inhibition was achieved in 29% of the patients treated with abciximab, 44% of those receiving eptifibatide, and 68% of the those receiving tirofiban (p = 0.02). In conclusion, at the evaluated doses, tirofiban seemed to be the most effective drug in achieving "optimal" platelet inhibition very early after percutaneous coronary intervention.

Comparison of Rapid Platelet Function Assay with Whole Blood Platelet Impedance Aggregometry for the Definition of Aspirin Resistance.

The reported incidence of aspirin (ASA) resistance ranges from 5 to 30%. Various platelet function assays have been employed to detect aspirin resistance in patients with cardio- and cerebrovascular disease. Such a high proposed incidence of ASA resistance poses a critical need for a rapid point-of -care (POC) platelet function test. Unfortunately, no uniformly accepted definition of ASA resistance exists. Platelet aggregation studies that have been used to define ASA resistance are time consuming and require special technical expertise. The Ultegra Rapid Platelet Function -ASA (RPFA-ASA) has been developed as a POC test that is performed without sample processing. This optical method measures agglutination of fibrinogen-coated beads upon platelet activation with arachidonic acid. In the presence of aspirin effect, however, the agglutination of the beads is inhibited. The described cutoff of ≥ 550 Aspirin Reaction Units (ARU) is termed non-responsiveness to ASA based on a preclinical study and subsequent correlation with epinephrine-induced platelet aggregation in platelet rich plasma. Since RPFA-ASA uses whole blood, we validated its performance characteristics against a classic whole blood platelet aggregation assay (WBA). We studied 50 healthy volunteers, aged 25–75 (24 men, 26 women) with normal CBC, who had not ingested anti-platelet drugs for 14 days prior to the study. Baseline studies included WBA (dual channel aggregometer, Chrono-log Inc., Havertown, PA) using both arachidonic acid (AA -0.5; 0.25 mM) and collagen (1; 2 μg/mL) as well as an RPFA-ASA assay (Accumetrics Inc., San Diego, CA). These studies were repeated after 3 days of ASA (325 mg/d) intake. Based on a review of the literature, we defined an adequate ASA response as a completely inhibited AA-induced platelet aggregation and at least 30% inhibition of collagen-induced aggregation (both concentrations of the agonist). Thus, those with < 30% inhibition of aggregation response to collagen were considered ASA resistant. Eleven subjects were ASA resistant by WBA (20%; 8 females and 3 males (aged 25–63). In contrast, since all 50 subjects achieved ARU values of < 550 ARU, none were recognized as an ASA non-responder by the RPFA-ASA. While the current cutoff of < 550 ARU posed by the Ultegra RPFA-ASA does identify those who have taken ASA, the assay is unable to recognize ASA non-responders. Thus, based on these data, the appropriate cutoff for the recognition of ASA resistance by the RPFA-ASA should be re-adjusted to a significantly lower level to ensure appropriate assay results.

Pharmacodynamics of two different dosing regimens of tirofiban in citrate or PPACK anticoagulated blood

The primary objective of this study was to compare the inhibitory activity of tirofiban measured with the rapid platelet function assay (RPFA) and with light transmission aggregometry using two different anticoagulants (citrate versus PPACK). Twenty patients treated with tirofiban for percutaneous coronary intervention were studied at six time points during tirofiban treatment. Tirofiban was given with a bolus dose of 10 µg/kg and an infusion of 0.10 µg/kg per min (10 patients) or with a bolus dose of 15 µg/kg and an infusion of 0.15 µg/kg per min (10 patients). Inhibition of platelet function appeared highest using citrated blood and the RPFA-device and lowest when assessed by aggregometry in PPACK-anticoagulated blood. Only the higher dose of tirofiban achieved an inhibition of platelet aggregation of at least 80% in all test systems.