Platelet Aggregation Pattern on Light Transmission Aggregometry Among Malaysian Healthy Individuals

@#Introduction: Platelet aggregation test using light transmission aggregometry (LTA) is considered as the gold standard for evaluation of platelet function. Variations of platelet aggregation had been reported in apparently healthy individuals whereby a normal cut–off value established locally is highly recommended. This study aims to determine the platelet aggregation pattern and the preliminary findings on reference values for multiple agonists–induced platelet aggregation among Malaysian healthy individuals in a single centre. Method: A total number of 63 informed consented healthy individuals consisted of Malay, Chinese and Indian were recruited among staff and blood donors at National Blood Centre, Kuala Lumpur. Platelet aggregation was measured using LTA against adenosine diphosphate 10 µM (ADP10), collagen 0.19 mg/mL (COL), ristocetin 1.5 mg/mL (RIS), arachidonic acid 1 mM (AA) and epinephrine 10 µM (EPI). Results were expressed as percent final aggregation (%FA). Reference values were calculated from mean±2SD. Results: Age, gender and ethnic groups had no significant effect on platelet aggregation. A variability of platelet aggregation response to EPI was observed among the healthy individuals. Ten of 33 respondents (30%) had impaired aggregation with <20% FA in response to EPI. The local population showed a slightly higher aggregation pattern in response to COL, RIS, AA and EPI (excluding non-responders) compared to manufacturer’s reference values. Conclusion: This study has provided a glimpse of the aggregation pattern of the local nationality showing considerable differences in the reference values from manufacturer’s; thus highlighting the need of establishing local reference values.

Platelet function tests: A 5-year audit of platelet function tests done for bleeding disorders in a tertiary care center of a developing country

Introduction: The platelet function disorders remain largely undiagnosed or incompletely diagnosed in developing nations due to lack of availability of tests like lumiaggregometry, granule release assay or molecular testing. We performed a retrospective analysis of all the platelet function test (PFT) carried out in past 5 years by Light transmission aggregometery (LTA) using a panel of agonist. The indications and the test results were analyzed by two hematopathologist with the aim to look into the present diagnostic facilities or lack of it for correct diagnosis. This is essential for better management and genetic counselling. Materials and Methods: The PFT was performed both on patients and healthy unrelated age specific controls by light transmission aggregometry on Chronolog platelet aggregometer using platelet rich plasma. The panel of agonists included ADP (10?m/l and 2.0 ?m/l), epinephrine (10.0 ?m/l), collagen (2?g/ml), arachidonic acid (0.75 mM) and ristocetin (1.25 mg/ml & 0.25 mg/l). Results: The 5 years records of 110 cases were audited, 101 of these were tested for clinical bleeding , 35 adults and 66 children. The adults included 29 women and 6 men, 17 to 82 years of age. The children were 16 years to 3 months of age, 30 girls and 36 boys. Platelet function test abnormality was found in 31.6% (32/101) cases ,a majority remained undiagnosed of these about 21% had clinically significant bleeding.The cases diagnosed included Glanzmann Thromboasthenia-11 , von Willebrand Disease-6, Bernard Soulier'syndrome-1, storage pool disorder-6, mild defect of Epinephrine-3, isolated defect with collagen in1. Conclusion: An epidemiologically large proportion of platelet function disorders amongst people living in developing nations remain undiagnosed. This lacunae needs to be highlighted and addressed on larger scale. The options available are to increase the available armamentarium of tests or international collaboration with a specialized laboratory to aid in complete diagnosis.

Research progress of platelet function tests in antiplatelet effect on monitoring P2Y12 receptor antagonist / 天津医药

The P2Y12 receptor antagonist is used widely in prevention and treatment of cardiovascular and cerebrovascular disease. Monitoring changes of platelet function after treatment can improve the prognosis of patients. The platelet function test is the important way to evaluate high residual platelet reactivity after antiplatelet treatment, including light transmission aggregometry (LTA), whole blood impedance aggregometry assay (WBIA), vasodilator- stimulated phosphoprotein (VASP), thrombelastogram (TEG), platelet function analyzer- 100 (PFA-100) and VerifyNow system (VerifyNow). It is very different for the reflecting ability with residual reactivity of platelets among these tests after anti-platelet therapy, and also significant difference for assessment effect. Among them, LTA is a classic method for the curative effect evaluation of anti-platelet agents, which is convenient and cheap, but it is susceptible to the operating and environment interference. The clinical application of WBIA is less, and which lacks threshold value for assessment. VASP is sensitive for the changes of platelet function, but the test is complex and expensive. TEG can monitor the inhibition ratio of drugs on anti-platelets, but it needs to verify the safety of treatment. It is not clear for sensitivity and specificity with monitoring anti-platelet agent by PFA-100. VerifyNow is effective and reliable, but the cost is high. The evidence of clinical study shows that LTA, VASP and VerifyNow can reflect the effect of platelet inhibition of P2Y12 receptor antagonists sensitively, and is associated with the risk of major adverse cardiac events (MACE) in patients with cadiovascular diseases.

Deciphering the platelet function test inacute coronary syndrome patients subjected to anti-platelet therapy / 中华检验医学杂志

Anti-platelet therapy plays a key role in acute coronary syndrome ( ACS ) treatments.Platelet function tests could monitor the effect of anti-platelet drugs′, however, it is still under debate that whether platelet function monitoring could be used to adjust antiplatelet therapy.Additionally, there are a number of platelet function assays, and each of them has specifically advantages and disadvantages.This article reviewed evidence-based information, guidelines, consensus and clinical experience about platelet function monitoring in ACS patients, which was intend to help laboratory technicians and clinicians understanding the value of platelet function tests in monitoring anti-platelet therapy.

An Assay of Measuring Platelet Reactivity Using Monoclonal Antibody against Activated Platelet Glycoprotein IIb/IIIa in Patients Taking Clopidogrel

BACKGROUND AND OBJECTIVES: Residual platelet reactivity in patients who are taking clopidogrel is commonly measured with VerifyNow assay, which is based on the principle of light transmission aggregometry. However, to evaluate the residual platelet reactivity, it would be more accurate if the reactivity of platelet glycoprotein (GP) IIb/IIIa is directly monitored. In this study, PAC1, a monoclonal antibody against activated platelet GP IIb/IIIa, was used to measure the residual platelet reactivity. SUBJECTS AND METHODS: Twenty seven patients with coronary artery disease taking clopidogrel were enrolled. Platelets in whole blood were stained with fluorescein isothiocyanate (FITC)-conjugated PAC1. Mean fluorescence intensity (MFI) and % positive platelets (PP) were measured with flow cytometry, and the binding index (BI; MFI x %PP/100) was calculated. P2Y12 reaction unit (PRU) and % inhibition of VerifyNow assay were also measured in the usual manner. RESULTS: PRU of VerifyNow assay correlated significantly with MFI, %PP, and BI at 10 microM (r=0.59, 0.73, and 0.60, respectively, all p<0.005) and 20 microM of adenosine diphosphate (ADP; r=0.61, 0.75, and 0.63, respectively, all p<0.005). The % inhibition also correlated significantly with MFI, %PP, and BI at 10 microM (r=-0.60, -0.69, and -0.59, respectively, all p<0.005) and 20 microM of ADP (r=-0.63, -0.71, and -0.62, respectively, all p<0.005). CONCLUSION: Direct measurements of the reactivity of platelet GP IIb/IIIa were feasible using PAC1 and flow cytometry in patients taking clopidogrel. Further clinical studies are required to determine the cut-off values which would define high residual platelet reactivity in patients on this treatment protocol.

A pharmacodynamic study of the optimal P2Y12 inhibitor regimen for East Asian patients with acute coronary syndrome

BACKGROUND/AIMS: Newer P2Y12 inhibitors, such as prasugrel and ticagrelor, have greater antiplatelet efficacy but may increase the risk of bleeding. In this study, we compared the pharmacodynamic efficacy of prasugrel and ticagrelor in East Asian patients with acute coronary syndrome (ACS). METHODS: We selected 83 ACS patients undergoing percutaneous coronary intervention who were discharged with 90 mg ticagrelor twice daily (n = 24), 10 mg prasugrel daily (n = 39) or 5 mg prasugrel daily (n = 20). After 2 to 4 weeks, on-treatment platelet reactivity (OPR) was assessed in terms of P2Y12 reaction units (PRUs) using the VerifyNow P2Y12 assay (Accumetrics). We compared East Asian (85 < PRU < or = 275) and Caucasian (85 < PRU < or = 208) criteria for assessing the therapeutic window of OPR. RESULTS: OPR was lowest in the ticagrelor group, followed by the 10 mg prasugrel and 5 mg prasugrel groups (49.1 ± 29.9 vs. 83.7 ± 57.1 vs. 168.5 ± 60.8, respectively; p < 0.001). The 5 mg prasugrel group had the highest proportion of patients with OPR values within the therapeutic window, followed by the 10 mg prasugrel and ticagrelor groups (90.0% vs. 46.2% vs. 12.5%, respectively; p < 0.001 for East Asian criteria; 60.0% vs. 43.6% vs. 12.5%, respectively; p < 0.001 for Caucasian criteria). CONCLUSIONS: Short-term administration of 5 mg prasugrel facilitated maintenance within the therapeutic window of OPR compared with the 10 mg prasugrel and ticagrelor groups. Thus, 5 mg prasugrel daily may be the optimal antiplatelet regimen for stabilized East Asian ACS patients.

Platelet function assay to determine the optimal preoperative cessation period of aspirin

BACKGROUND: This study was conducted to assess preoperative residual antiplatelet-induced platelet dysfunction using a platelet function assay to determine the optimal cessation period of aspirin during the preoperative period. METHODS: Patients older than 20 years, who were scheduled for elective surgery under general anesthesia, were enrolled prospectively. The last ingestion of the aspirin had occurred within the previous 10 days before surgery (aspirin 100 mg per day). No history of antiplatelet intake was documented in the control group. Platelet function was assessed using a platelet function analyzer-100 (PFA-100). Receiver operating characteristic (ROC) curves were plotted to determine the ability of aspirin cessation time in order to predict platelet function as assessed by the PFA. Patients were assigned to groups according to the period of aspirin discontinuation. RESULTS: Two hundred patients were enrolled in this study (100 control group and 100 aspirin group). The mean PFA value of the control group was significantly lower than that of the treated groups. The areas under the ROC curve (0.65, P = 0.03) of aspirin cessation period to discriminate PFA prolongation were significant. There were significant decreases in PFA values when aspirin medication was discontinued for 7 days, but not when the intake was discontinued for 5 days. CONCLUSIONS: Platelet function recovered if aspirin intake was discontinued > 7 days prior to surgery; therefore, in these patients, a preoperative platelet function test is not essential. However, the residual antiplatelet effect of aspirin should be assessed using the PFA in patients who discontinue aspirin less than 7 days prior to surgery.

Aspirin Resistance May Not Be Associated with Clinical Outcome after Acute Ischemic Stroke: Comparison with Three Different Platelet Function Assays / 대한뇌졸중학회지

BACKGROUND: Aspirin resistance (AR) in platelet function assays showed substantial variation depending on the methods used to evaluate it. METHODS: In this study, we prospectively compared the results of Multiplate impedance platelet aggregometry (IPA) with those of light transmission aggregometry (LTA) and VerifyNow(R) system in determination of the prevalence of aspirin resistance (AR) and investigated the correlation between its presence and poor outcome (modified Rankin scale >2) in 105 patients with aspirin after acute ischemic stroke (AIS). RESULTS: After 5 days of using aspirin, 15 patients (14.3%) were classified as aspirin-resistance with the use of IPA, 24 patients (22.9%) by the LTA, and 14 patients (13.3%) by VerifyNow. Good agreement between the results of IPA and VerifyNow, was found (R=0.674, P<0.01). The concordance rate of AR detection was high between VerifyNow and IPA (k=0.72, P<0.01), albeit quite low between LTA and IPA. Regarding on its influence on clinical outcome after AIS, there wasn't any significant relationship between occurrence of poor outcome and the presence of AR in three platelet function assays. CONCLUSION: This study reveals that the incidence of AR in AIS might be highly test-specific. IPA seems to be similar to VerifyNow as a platelet function test.

Platelet Function Assay for Clopidogrel and Ticlopidine in Patients With Ischemic Stroke

BACKGROUND: The rapid platelet function assay (RPFA) has recently been developed and used to monitor the antiplatelet effects on the P2Y12 ADP receptor. We describe the platelet response to clopidogrel and ticlopidine using the RPFA and identify the clinical factor related to laboratory resistance in patients with ischemic stroke. METHODS: Of the 172 outpatients with ischemic stroke or transient ischemic attack (TIA) enrolled in this study, 86 were taking clopidogrel (75 mg/day) and 86 were taking ticlopidine (500 mg/day). Demographic data, vascular risk factors, stroke subtypes, and the results of blood tests were recorded. Inhibition is described as the percentage change from baseline aggregation, and is calculated from the P2Y12 reaction unit (PRU) and the base PRU on the RPFA. Those patients who displayed ineffective aggregation-inhibition (inhibition <20%) on the RPFA were defined as nonresponders. RESULTS: The response of platelet aggregation-inhibition to clopidogrel and ticlopidine exhibited a variable distribution (PRU; coefficient of variability, 0.477). Ineffective platelet inhibition was detected in 25.6% of the clopidogrel group and 3.5% of the ticlopidine group (p<0.001). In addition to clopidogrel, TIA and diabetes exhibited significantly higher ineffective platelet inhibition in a univariate analysis. In the multivariate analysis, clopidogrel and TIA remained significant, and diabetes fell to borderline significance (p=0.061). CONCLUSIONS: The response to clopidogrel and ticlopidine can vary between patients. Platelet inhibition is lower for clopidogrel than for ticlopidine on the platelet function test in patients with ischemic stroke. The clinical impact of these results remains uncertain; further investigations are needed.

Monitoring Platelet Inhibition by Clopidogrel Using Rapid Platelet Function Assay in Patients With Ischemic Stroke

BACKGROUND: Clopidogrel inhibits platelet P2Y12 adenosine diphosphate (ADP) receptors and has been widely used in patients with ischemic stroke. However, a considerable number of patients suffer from cerebrovascular events despite the use of clopidogrel. The rapid platelet function assay (RPFA) has been used for monitoring the antiplatelet effects on the P2Y12 ADP receptor. This study was performed to measure the platelet response to clopidogrel using RPFA in patients with ischemic stroke, and to identify the clinical factor related with clopidogrel resistance. METHODS: A total of 86 patients taking clopidogrel (75 mg/day) were enrolled. Demographic data, vascular risk factors, the presence of obesity and metabolic syndrome, drug history, hemoglobin, platelet counts, and stroke subtypes were recorded. RPFA presented the results as P2Y12 Reaction Units (PRU), base PRU (BASE), and Inhibition (%). Inhibition was calculated as (1-PRU/BASE)x100. The patients showing ineffective aggregation- inhibition (percentage of Inhibition < 20) on RPFA were defined as non-responders to clopidogrel. RESULTS: The response of platelet aggregation-inhibition to clopidogrel showed a variable distribution with mean and standard deviation of 32.2+/-22.3%. Twenty four (27.9%) patients showed the inhibition below 20%. There was no difference between responders and non-responders regarding the clinical factors above. We found no influence of co-medication with the statins on platelet response to clopidogrel. CONCLUSIONS: There is a patient variability in response to clopidogrel and a considerable portion of stroke patients have clopidogrel resistance on the platelet function test. The clinical usefulness of routine platelet function test requires further validation.

Changes of platelet and blood coagulating function during endovascular graft exclusion / 第二军医大学学报

Objective:To study the changes of platelet and blood coagulating function during endovascular graft exclusion(EVGE), providing reference for reasonable use of heparin and platelet. Methods:Using sonoclot analysis (SCT), 20 patients accepted EVGE were measured for ACT, clot rate, platelet function and hematocrit (HCT) and platelet count (PLT) after anesthesia induction(T 1), heparination(0.3 0.5 mg/kg)(T 2) and EVGE(T 3), respectively. The reasons for variability were analyzed. Results:ACT, clot rate and blood platelet function were normal at T 1. At T 2 ACT was prolonged [(289? 61.1) s,] clot rate and platelet function were decreased ( P