Evaluation of a diagnostic platelet aggregation test strategy for platelet rich plasma samples with low platelet counts

INTRODUCTION

Light transmission aggregometry (LTA) is important for diagnosing platelet function disorders (PFD) and von Willebrand disease (VWD) affecting ristocetin-induced platelet aggregation (RIPA). Nonetheless, data is lacking on the utility of LTA for investigating thrombocytopenic patients and platelet rich plasma samples with low platelet counts (L-PRP). Previously, we developed a strategy for diagnostic LTA assessment of L-PRP that included: (1) acceptance of referrals/samples, regardless of thrombocytopenia severity, (2) tailored agonist selection, based on which are informative for L-PRP with mildly or severely low platelet counts, and (3) interpretation of maximal aggregation (MA) using regression-derived 95% confidence intervals, determined for diluted control L-PRP (C-L-PRP).

METHODS

To further evaluate the L-PRP LTA strategy, we evaluated findings for a subsequent patient cohort.

RESULTS

Between 2008 and 2021, the L-PRP strategy was applied to 211 samples (11.7% of all LTA samples) from 192 unique patients, whose platelet counts (median [range] × 109 /L) for blood and L-PRP were: 105 [13-282; 89% with thrombocytopenia] and 164 [17-249], respectively. Patient-L-PRP had more abnormal MA findings than simultaneously tested C-L-PRP (p-values <0.001). Among patients with accessible electronic medical records (n = 181), L-PRP LTA uncovered significant aggregation abnormalities in 45 (24.9%), including 18/30 (60%) with <80 × 109  platelets/L L-PRP, and ruled out PFD, and VWD affecting RIPA, in others. The L-PRP LTA strategy helped diagnose VWD affecting RIPA, Bernard Soulier syndrome, familial platelet disorder with myeloid malignancy, suspected ITGA2B/ITGB3-related thrombocytopenia, and acquired PFD.

CONCLUSION

Diagnostic LTA with L-PRP, using a strategy that considers thrombocytopenia severity, is feasible and informative.

Altered whole blood thrombin generation and hyperresponsive platelets in patients with pancreatic cancer

BACKGROUND

Thromboembolic disease is a major complication in patients with pancreatic ductal adenocarcinoma (PDAC). Patients with PDAC often have altered blood cell counts, which are associated with venous thromboembolism (VTE) development. The high thrombotic risk in patients with PDAC may be partially caused by procoagulant blood cells.

OBJECTIVES

The aim of this study was to compare blood cell-dependent coagulation between patients with PDAC (n = 18) and healthy controls matched for age and sex (n = 18).

METHODS

Thrombin generation (TG) was measured in whole blood (WB) and plasma. The capacity of platelets to release granules (PGRCs) was measured in WB. We explored the occurrence of thromboembolic events in patients with PDAC during a 6-month follow-up.

RESULTS

Patients showed an increased endogenous thrombin potential in WB compared with controls. This difference was not observed in plasma, indicating a procoagulant effect of blood cells. Both in WB and plasma, the lag time was prolonged in patients compared with controls. Patients had hyperresponsive platelets, with a shorter time to peak granule release. Of the 18 patients with PDAC, 4 developed a venous thromboembolism (22%) and 1 developed an arterial thrombosis (6%). A shorter lag time in WB, but not in plasma, and an increased PGRC were associated with thromboembolic events.

CONCLUSION

Patients with PDAC have an increased and delayed WB TG coagulation profile compared with controls. A shorter lag time in WB TG and increased PGRC are associated with the incidence of thromboembolic events. Platelets appear to be key players in thrombosis development. Measuring hemostasis in WB could improve thrombosis risk estimation in patients with PDAC.

Cold-stored platelet hemostatic capacity is maintained for three weeks of storage and associated with taurine metabolism

BACKGROUND

Platelet (PLT) product transfusion is a life-saving therapy for actively bleeding patients. There is an urgent need to maintain PLT function and extend shelf life to improve outcomes in these patients. Cold-stored PLT (CS-PLT) maintain hemostatic potential better than room temperature-stored PLT (RT-PLT). However, whether function in long-term CS-PLT is maintained under physiological flow regimes and/or determined by cold-induced metabolic changes is unknown.

OBJECTIVES

This study aimed to (i) compare the function of RT-PLT and CS-PLT under physiological flow conditions, (ii) determine whether CS-PLT maintain function after 3 weeks of storage, and (iii) identify metabolic pathways associated with the CS-PLT lesion.

METHODS

We performed phenotypic and functional assessments of RT- and CS-PLT (22 °C and 4 °C storage, respectively; N = 10 unique donors) at storage days 0, 5, and/or 21 via metabolomics, flow cytometry, aggregation, thrombin generation, viscoelastic testing, and a microfluidic assay to measure primary hemostatic function.

RESULTS

Day 21 4 °C PLT formed an occlusive thrombus under arterial shear at a similar rate to day 5 22 °C PLT. Day 21 4 °C PLTs had enhanced thrombin generation capacity compared with day 0 PLT and maintained functionality comparable to day RT-PLT across all assays performed. Key metrics from microfluidic assessment, flow cytometry, thrombin generation, and aggregation were associated with 4 °C storage, and metabolites involved in taurine and purine metabolism significantly correlated with these metrics. Taurine supplementation of PLT during storage improved hemostatic function under flow.

CONCLUSION

CS-PLT stored for 3 weeks maintain hemostatic activity, and storage-induced phenotype and function are associated with taurine and purine metabolism.

Impact of lipid emulsions in parenteral nutrition on platelets: a literature review

Lipid emulsions are essential components of parenteral nutrition solutions that provide energy and essential fatty acids. The complexity of the formulations of lipid emulsions may lead to adverse outcomes such as platelet reactivity and changes in platelet aggregation and related coagulation. Platelets are responsible for haemostasis; they activate and demonstrate morphological changes upon extracellular factors to maintain blood fluidity and vascular integrity. Although parenteral nutrition lipid emulsions are generally found safe with regard to modulation of platelet activity, studies are still accumulating. Thus, this review aims to investigate platelet-related changes by parenteral nutrition lipid emulsions in human studies. Studies have pointed out patients at risk of bleeding and increased platelet aggregation responses due to the administration of lipid emulsions. Lipid emulsions may further benefit patients at high risk of thrombosis due to anti-thrombotic effects and should be cautiously used in patients with thrombocytopenia. The reported platelet-related changes might be associated with the fatty acid change in the plasma membranes of platelets following changes in platelet synthesis and plasma levels of eicosanoids. In conclusion, studies investigating platelets and parenteral nutrition should be supported to minimize the adverse effects and to benefit from the potential protective effects of parenteral nutrition lipid emulsions.

Standardization of definition and management for bleeding disorder of unknown cause: communication from the SSC of the ISTH

In many patients referred with significant bleeding phenotype, laboratory testing fails to define any hemostatic abnormalities. Clinical practice with respect to diagnosis and management of this patient cohort poses significant clinical challenges. We recommend that bleeding history in these patients should be objectively assessed using the International Society on Thrombosis and Haemostasis (ISTH) bleeding assessment tool. Patients with increased bleeding assessment tool scores should progress to hemostasis laboratory testing. To diagnose bleeding disorder of unknown cause (BDUC), normal complete blood count, prothrombin time, activated partial thromboplastin time, thrombin time, von Willebrand factor antigen, von Willebrand factor function, coagulation factors VIII, IX, and XI, and platelet light transmission aggregometry should be the minimum laboratory assessment. In some laboratories, additional specialized hemostasis testing may be performed to identify other rare causes of bleeding. We recommend that patients with a significant bleeding phenotype but normal laboratory investigations should be registered with a diagnosis of BDUC in preference to other terminology. Global hemostatic tests and markers of fibrinolysis demonstrate variable abnormalities, and their clinical significance remains uncertain. Targeted genomic sequencing examining candidate hemostatic genes has a low diagnostic yield. Underlying BDUC should be considered in patients with heavy menstrual bleeding since delays in diagnosis often extend to many years and negatively impact quality of life. Treatment options for BDUC patients include tranexamic acid, desmopressin, and platelet transfusions.

A novel technique to quantify the kinetics of blood clot contraction based on the expulsion of fluorescently labeled albumin into serum

BACKGROUND

The platelet-driven contraction or retraction of blood clots has been utilized to obtain blood serum for laboratory studies, but now, in vitro clot contraction assays are used in research laboratories and clinics to assess platelet functionality. The static final extent of clot contraction measured using a clot size or expelled serum volume can be supplemented substantially with a dynamic analysis.

OBJECTIVES

To provide a step-by-step protocol for a relatively simple and affordable new automated methodology to follow the kinetics of blood clot contraction, which allows for simultaneous measurements of various samples at a time and requires only a fluorescence plate reader.

METHODS

The kinetics of clot contraction in whole blood was assessed by continuously detecting the fluorescence intensity of fluorescein isothiocyanate-albumin added to a blood sample before clotting and expelled into the serum during clot shrinkage.

RESULTS

The clots are formed and fluorescence is measured in the wells of a black multiwell plate using a standard plate fluorescent reader. The specificity of this technique for clot contraction has been demonstrated by the strong inhibitory effects of blebbistatin, latrunculin A, and abciximab. To validate the new technique, increased fluorescence intensity in the contracting clots was measured in parallel with a visual decrease in clot size performed with the same blood samples.

CONCLUSION

The resulting clot contraction dynamics based on the expulsion of fluorescein isothiocyanate-albumin can be quantified using a number of kinetic parameters as well as a phase kinetics analysis. The advantages and drawbacks of the new technique are discussed.

Association of laboratory test results with the bleeding history in patients with inherited platelet function disorders (the Bleeding Assesment Tool - LABoratory tests substudy): communication from the Platelet Physiology ISTH-SSC

Background

In hemophilia and von Willebrand disease, the degree of alteration of laboratory assays correlates with bleeding manifestations. Few studies have assessed the predictive value for bleeding of laboratory assays in patients with inherited platelet function disorders (IPFDs).

Objectives

To assess whether there is an association between platelet function assay results and bleeding history, as evaluated by the International Society on Thrombosis and Haemostasis (ISTH) bleeding assessment tool (BAT).

Methods

Centers participating in the international ISTH-BAT validation study were asked to provide results of the diagnostic assays employed for the patients they enrolled, and the association with the individual patients' bleeding score (BS) was assessed.

Results

Sixty-eight patients with 14 different IPFDs were included. Maximal amplitude of platelet aggregation was significantly lower in patients with a pathologic BS and correlated inversely with the BS, a finding largely driven by the subgroup of patients with Glanzmann thrombasthenia and CalDAG-GEFI deficiency; after their exclusion, TRAP-induced aggregation remained significantly lower in patients with a pathologic BS. Bleeding time was significantly more prolonged in patients with a high BS than in those with a normal BS (27.1 ± 6.2 minutes vs 15.1 ± 10.6 minutes; P < .01). Reduced α-granule content was significantly more common among patients with a pathologic BS than among those with a normal BS (80% vs 20%; P < .05). Receiver operating characteristic curve analysis revealed a significant discriminative ability of all the aforementioned tests for pathologic BS (P < .001), also after exclusion of patients with Glanzmann thrombasthenia and CalDAG-GEFI deficiency.

Conclusion

This study shows that altered platelet laboratory assay results are associated with an abnormal ISTH-BAT BS in IPFD.

Coagulation Testing in Real-World Setting: Insights From a Comprehensive Survey

The objective of this survey was to gain a real-world perspective on coagulation testing by evaluating the availability of various coagulation laboratory tests, assessing specific analytic and postanalytic steps in clinical laboratories in Korea.Participants were surveyed using a 65-question questionnaire specifically focused on their coagulation testing practices related to prothrombin time (PT), activated partial thromboplastin time (aPTT), plasma-mixing studies, lupus anticoagulant (LA) tests, platelet function tests, coagulation factor assays, and the composition of hemostasis and thrombosis test panels. The survey was performed between July and September 2022.The survey achieved a 77.9% (81 of 104) response rate. PT or aPTT tests were performed directly at all participating institutions, followed by D-dimer and fibrinogen tests, platelet function test, and plasma-mixing studies in order of frequency. Variations existed in the performance of mixing test and LA assessment. Patterns of coagulating testing differed depending on the size of the hospital. The survey revealed that most laboratories conducted coagulation tests following the international guidelines such as Clinical Laboratory Standards Institute guidelines and the Korean Laboratory Certification system. However, some coagulation tests, including mixing test and LA tests, are yet to be standardized in Korea.Continuous education on coagulation test methods and internal and external quality control are required to encourage laboratories to enhance the performance of coagulation testing.

Preanalytical conditions for multiparameter platelet flow cytometry

Background

Flow cytometry is an important technique for understanding multiple aspects of blood platelet biology. Despite the widespread use of the platform for assessing platelet function, the optimization and careful consideration of preanalytical conditions, sample processing techniques, and data analysis strategies should be regularly assessed. When set up and designed with optimal conditions, it can ensure the acquisition of robust and reproducible flow cytometry data. However, these parameters are rarely described despite their importance.

Objectives

We aimed to characterize the effects of several preanalytical variables on the analysis of blood platelets by multiparameter fluorescent flow cytometry.

Methods

We assessed anticoagulant choice, sample material, sample processing, and storage times on 4 distinct and commonly used markers of platelet activation, including fibrinogen binding, expression of CD62P and CD42b, and phosphatidylserine exposure.

Results

The use of suboptimal conditions led to increases in basal platelet activity and reduced sensitivities to stimulation; however, the use of optimal conditions protected the platelets from artifactual stimulation and preserved basal activity and sensitivity to activation.

Conclusion

The optimal preanalytical conditions identified here for the measurement of platelet phenotype by flow cytometry suggest a framework for future development of multiparameter platelet assays for high-quality data sets and advanced analysis.

The rate of platelet activation determines thrombus size and structure at arterial shear

BACKGROUND

The response of platelets to activating stimuli and pharmaceutical agents varies greatly within the normal population. Current platelet function tests measure endpoint levels of platelet activation without taking the speed at which platelets activate into account, potentially missing vital metrics to characterise platelet reactivity.

OBJECTIVES

To identify variability, to agonist and between individuals, in platelet activation kinetics and assess the impact of this on thrombus formation.

METHODS

We have developed a bespoke real-time flow cytometry assay and analysis package that measures the rate of platelet activation over time using two parameters of platelet activation, fibrinogen binding and P-selectin exposure.

RESULTS

The rate of platelet activation varied considerably within the normal population but did not correlate with maximal platelet activation, demonstrating that platelet activation rate is a separate and novel metric to describe platelet reactivity. The relative rate of platelet response between agonists was strongly correlated, suggesting a central control mechanism regulates the rate of platelet response to all agonists.

CONCLUSIONS

For the first time, we have shown that platelet response rate corresponds to thrombus size and structure, where faster responders form larger, more densely packed thrombi at arterial, but crucially not venous shear. We have demonstrated that the rate of platelet activation is an important metric in stratifying individual platelet responses and will provide a novel focus for the design and development of anti-platelet therapy, targeting high shear thrombosis without exacerbating bleeding at low shear.

Postinjury platelet aggregation and venous thromboembolism

BACKGROUND

Posttraumatic venous thromboembolism (VTE) remains prevalent in severely injured patients despite chemoprophylaxis. Importantly, although platelets are central to thrombosis, they are not routinely targeted in prevention of posttraumatic VTE. Furthermore, platelets from injured patients show ex vivo evidence of increased activation yet impaired aggregation, consistent with functional exhaustion. However, the relationship of this platelet functional phenotype with development of posttraumatic VTE is unknown. We hypothesized that, following injury, impaired ex vivo platelet aggregation (PA) is associated with the development of posttraumatic VTE.

METHODS

We performed a secondary analysis of 133 severely injured patients from a prospective observational study investigating coagulation and inflammation (2011-2019). Platelet aggregation in response to stimulation with adenosine diphosphate (ADP), collagen, and thrombin was measured at presentation (preresuscitation) and 24 hours (postresuscitation). Viscoelastic clot strength and lysis were measured in parallel by thromboelastography. Multivariable regression examined relationships between PA at presentation, 24 hours, and the change (δ) in PA between presentation and 24 hours with development of VTE.

RESULTS

The 133 patients were severely injured (median Injury Severity Score, 25), and 14% developed VTE (all >48 hours after admission). At presentation, platelet count and PA were not significantly different between those with and without incident VTE. However, at 24 hours, those who subsequently developed VTE had significantly lower platelet counts (126 × 10 9 /L vs. 164 × 10 9 /L, p = 0.01) and lower PA in response to ADP ( p < 0.05), collagen ( p < 0.05), and thrombin ( p = 0.06). Importantly, the magnitude of decrease in PA (δ) from presentation to 24 hours was independently associated with development of VTE (adjusted odds ratios per 10 aggregation unit decrease: δ-ADP, 1.31 [ p = 0.03]; δ-collagen, 1.36 [ p = 0.01]; δ-thrombin, 1.41 [ p < 0.01]).

CONCLUSION

Severely injured patients with decreasing ex vivo measures of PA despite resuscitation have an increased risk of developing VTE. This may have implications for predicting development of VTE and for studying platelet targeted chemoprophylaxis regimens.

LEVEL OF EVIDENCE

Prognostic/Epidemiological; Level III.

Arterial and venous blood sampling is equally applicable for coagulation and fibrinolysis analyses

OBJECTIVES

No consensus exists upon whether arterial and venous blood samples are equivalent when it comes to coagulation analyses. We therefore conducted a comparative cohort study to clarify if arteriovenous differences affect analyses of primary and secondary hemostasis as well as fibrinolysis.

METHODS

Simultaneous paired blood samplings were obtained from a cannula in the radial artery and an antecubital venipuncture in 100 patients immediately before or one day after thoracic surgery. Analyses of platelet count and aggregation, International Normalized Ratio (INR), activated partial thromboplastin time (APTT), antithrombin, thrombin time, fibrinogen, D-dimer, rotational thromboelastometry (ROTEM), thrombin generation, prothrombin fragment 1 + 2, and an in-house dynamic fibrin clot formation and lysis assay were performed.

RESULTS

No differences were found between arterial and venous samples for the far majority of parameters. The only differences were found in INR, median (IQR): venous, 1.1 (0.2) vs. arterial, 1.1 (0.2) (p<0.002) and in prothrombin fragment 1 + 2: venous, 289 (209) pmol/L vs. arterial, 279 (191) pmol/L (p<0.002).

CONCLUSIONS

The sampling site does not affect the majority of coagulation analyses. Small differences were found for two parameters. Due to numerically very discrete differences, they are of no clinical relevance. In conclusion, the present data suggest that both samples obtained from arterial and venous blood may be applied for analyses of coagulation and fibrinolysis.

Reduced platelet function in preterm neonates compared with term neonates

Background

A reduced platelet function might contribute to the longer bleeding time seen in preterm neonates. However, the previously used platelet function testing in neonates is limited due to methodological limitations, mainly caused by difficulties in obtaining adequate blood volume. Therefore, the platelet function in preterm neonates is sparsely investigated. The aim of this study was to compare platelet function in preterm neonates at birth and at expected term age with platelet function in term neonates at birth.

Methods

We included 43 preterm neonates born at gestational age (GA) 28 + 0 to 34 + 0 and 21 term neonates born at GA 38 + 0 to 41 + 0. Within the first 24 hours of life, 1-1.5 mL peripheral blood was obtained and for preterm neonates, resampling was performed at expected term age (GA 38 + 0 to 41 + 0). Platelet function testing included impedance aggregometry and platelet activation measured by flow cytometry. In addition, platelet count was determined.

Results

Platelet count and platelet activation were reduced in preterm neonates compared with term neonates at birth, but we found no difference in impedance aggregometry at birth. At expected term age, platelet count and aggregation exceeded term levels, but platelet activation remained impaired in the preterm.

Conclusion

Preterm neonatal function is decreased at birth and does not seem to reach term levels during the first 4 to 13 weeks of life.

Effects of ex vivo blood anticoagulation and preanalytical processing time on the proteome content of platelets

BACKGROUND

Ex vivo assays of platelet function critically inform mechanistic and clinical hematology studies, where effects of divergent blood processing methods on platelet composition are apparent, but unspecified.

OBJECTIVE

Here, we evaluate how different blood anticoagulation options and processing times affect platelet function and protein content ex vivo.

METHODS

Parallel blood samples were collected from healthy human donors into sodium citrate, acid citrate dextrose, EDTA or heparin, and processed over an extended time course for functional and biochemical experiments, including platelet proteome quantification with multiplexed tandem mass tag (TMT) labeling and triple quadrupole mass spectrometry (MS).

RESULTS

Each anticoagulant had time-dependent effects on platelet function in whole blood. For instance, heparin enhanced platelet agonist reactivity, platelet-monocyte aggregate formation and platelet extracellular vesicle release, while EDTA increased platelet α-granule secretion. Following platelet isolation, TMT-MS quantified 3357 proteins amongst all prepared platelet samples. Altogether, >400 proteins were differentially abundant in platelets isolated from blood processed at 24 h versus 1 h post-phlebotomy, including proteins pertinent to membrane trafficking and exocytosis. Anticoagulant-specific effects on platelet proteomes included increased complement system and decreased α-granule proteins in platelets from EDTA-anticoagulated blood. Platelets prepared from heparinized blood had higher levels of histone and neutrophil-associated proteins in a manner related to neutrophil extracellular trap (NET) formation and platelet:NET interactions in whole blood ex vivo.

CONCLUSION

Our results demonstrate that different anticoagulants routinely used for blood collection have varying effects on platelets ex vivo, where methodology-associated alterations in platelet proteome may influence mechanistic, translational and biomarker studies.

Comprehensive phenotyping of human platelets by single-cell cytometry

Platelets are small anucleate blood cells that contribute to hemostasis, immunity, and inflammation. Circulating platelets are heterogeneous in size, age, receptor expression, and reactivity. They inherit many features from megakaryocytes and are further modified on exposure to bioactive substances in the bloodstream. Among these substances, prothrombotic agonists, vasodilators, and bloodborne pathogens modulate platelet phenotypes via distinct signaling cascades. The ability of platelets to respond to (patho)physiologic signals is incompletely understood but likely depends on their repertoire of surface receptors, which may partition them into discrete subsets with specialized functions and divergent abilities. The single-cell resolution of flow and mass cytometry is ideal for immunophenotyping and allows the identification of platelet subsets in remarkable detail. In this report, we describe the surface markers and gating strategies needed for the comprehensive characterization of platelets.

Blood loss after coronary artery bypass by aspirin responsiveness assessed with preoperative VerifyNow aspirin testing

BACKGROUND

Aspirin is important for preventing thrombotic events but also increases bleeding complications. Minimizing bleeding while preventing thrombotic events remains challenging in patients undergoing coronary artery bypass grafting (CABG). Establishing the patient's preoperative aspirin response could distinguish patients at risk for perioperative blood loss.

OBJECTIVE

Aim was to compare 12-h blood loss after CABG between aspirin-sensitive and aspirin-resistant patients.

PATIENTS/METHODS

The primary analysis of this substudy of the POPular CABG trial (NCT02352402) included patients that used aspirin monotherapy preoperatively. A preoperative platelet function test by the VerifyNow aspirin assay was performed before CABG and patients were classified as aspirin-sensitive or aspirin-resistant based on an aspirin reaction units cutoff value of 550. The primary end point was 12-hour blood loss after CABG. The secondary end point was, among others, clinical bleeding events after CABG.

RESULTS

A total of 128 patients were included in the primary analysis. Of these, 116 patients were aspirin sensitive and 12 were aspirin resistant. Mean blood loss 12 hours after CABG was 555 ± 278 mL in aspirin-sensitive patients and 406±110 mL in aspirin-resistant patients (P = .04). All bleeding events (n = 15; 11.7%) occurred in aspirin-sensitive patients.

CONCLUSIONS

In patients who are on aspirin preoperatively, aspirin sensitivity was associated with 12-hour blood loss after CABG, suggesting that preoperative VerifyNow aspirin testing could identify patients undergoing CABG at high risk for perioperative bleeding.

[Platelet function tests and Chinese medicines with antiplatelet function:a review]

Platelet function tests have been increasingly used to assist in the diagnosis of platelet disorders and prethrombotic state, monitoring of the efficacy of antiplatelet therapies, and personalized treatment. On the basis of light transmission aggregometry, new methods for platelet function test have been developed successively. At present, the research and development of platelet function detector is in its infancy in China. The active constituents of antiplatelet Chinese medicines can be classified into terpenoids, flavonoids, saponins, organic acids, lignans, diketones, volatile oils, and stilbenes. The results of dose-antiplatelet effect relationship of Chinese medicines and the active constituents showed that the effective concentration of the extracts or monomers of Chinese medicines was at micromolar level(μmol·L~(-1)), among which salvianolic acid B and ginkgolide K, ginkgolide B, and ginkgolide A had the strongest antiplatelet effect. These results suggest that the antiplatelet effect of Chinese medicine may be weaker than that of chemical drugs and biological products. Therefore, it is necessary to explore the structure-activity relationship of the active constituents in existing Chinese medicines and further improve their efficacy through structure modification. The antiplatelet effect of Chinese medicines and the constituents involves multiple pathways and multiple targets. These research results provide a reference for clinical application of them. However, there is still a lack of large-scale multi-center clinical trials to confirm the efficacy and safety of them. The regularity of the relationship between the structures of various constituents and their corresponding functions is still unknown and the relevant signal transduction pathways and structure-activity relationship need to be further studied. This paper summarized and analyzed the determination methods of platelet functions and the research results of antiplatelet Chinese medicines, which is of reference value for the research of effective and safe antiplatelet Chinese medicines.

Whole blood dynamic platelet aggregation counting and 1-year clinical outcomes in patients with coronary heart diseases treated with clopidogrel

In the setting of coronary heart diseases (CHDs) on treatment with clopidogrel, ADP-induced platelet aggregation has been demonstrated with ischemic events. However, there were very limited data for predicting ischemic events by platelet function test via dynamic platelet aggregation counting (DPAC). The present study aimed to evaluate the relationship between adenosine diphosphate (ADP)-induced whole blood platelet aggregation rates (PARs) and clinical outcomes in patients with CHDs on treatment with clopidogrel. We have retrospectively analyzed the clinical data of consecutive patients with CHDs based on the electronic medical records between May 2016 and December 2018. The primary endpoint was a composite endpoint events (CEEs) of ischemic cardiovascular events (including acute coronary syndrome, heart failure, transient ischemic attack, and cerebral infarction) and all-cause death. A total of 490 patients (mean age 66.6 years, 71% man) were received ADP-induced PARs via DPAC. On follow-up (mean 374 days), 107 subjects (21.8%) developed CEEs. Cox regression analysis indicated that the risk of CEEs was independently associated with ADP-induced whole blood PARs [HR: 1.023, 95% CI: 1.005-1.041, P = .011]. The distribution of CYP2C19 loss of function gene was higher in patients with on-treatment platelet hyperresponsiveness (10/12 vs 38/75, P = .042). In conclusion, ADP-induced whole blood PARs via DPAC is feasible, which can predict the incidence of 1-year CEEs in patients with CHDs on treatment with clopidogrel. CYP2C19 gene polymorphism was associated with clopidogrel on-treatment platelet hyperresponsiveness.

Immunophenotypic Analysis of Platelets by Flow Cytometry

Platelets are small but very abundant blood cells that play a key role in hemostasis, contributing to thrombus formation at sites of injury. The ability of platelets to perform this function, as well as functions in immunity and inflammation, is dependent on the presence of cell surface glycoproteins and changes in their quantity and conformation after platelet stimulation. In this article, we describe the characterization of platelet surface markers and platelet function using platelet-specific fluorescent probes and flow cytometry. Unlike traditional platelet tests, immunophenotypic analysis of platelets by flow cytometry allows the analysis of platelet function in samples with very low platelet counts as often encountered in clinical situations. © 2021 Wiley Periodicals LLC. Basic Protocol 1: Immunophenotyping of platelet surface receptors Alternate Protocol: Fix-first method for immunophenotyping of platelet surface receptors Basic Protocol 2: Determination of platelet activation using P-selectin expression and/or PAC1 binding Basic Protocol 3: Determination of procoagulant platelets using annexin V binding or antibodies specific for coagulation factor V/Va or X/Xa Support Protocol: Preparation of isolated platelets.

Platelet function assays for the diagnosis of aspirin resistance

Aspirin, an antiplatelet drug, is commonly used at low doses for numerous indications, including prophylaxis of cardiovascular, neurovascular, and venous thromboembolic events. Due to review articles suggesting that aspirin resistance may result in poorer outcomes, interest in assessing platelet function is increasing. Despite this, platelet function tests are rarely used as part of routine clinical practice and therefore, a basic understanding of these tests may be lacking. Although aspirin resistance can be categorized as clinical or laboratory resistance, determining laboratory resistance is the only way to determine resistance before treatment failure occurs. Therefore, knowledge of platelet assays to determine aspirin resistance is of importance. The following review aims to provide a framework for clinicians to understand the main principles of platelet function tests. This includes comparison of the most frequently used platelet assays to diagnose aspirin resistance, including the basic mechanism, methodology, reference ranges, inter-assay comparison, and their respective clinical considerations when using.

Platelet Immunophenotyping by High-Dimensional Mass Cytometry

Platelets are small blood cells that contribute to hemostasis, immunity, and inflammation. Characterization of platelet surface markers allows for differentiation of activated platelets from resting platelets, diagnosis of platelet disorders, and investigation of platelet biology and pathology. In this article, we describe the use of mass cytometry or "CyTOF" (mass spectroscopy detection of metal-tagged antibodies on individual cells) to measure a large number of markers on each platelet and to identify platelet subsets based on the shared expression of multiple markers. This powerful new approach provides a vastly more detailed picture of platelet immunophenotypes than conventional flow cytometry and enables investigation of the roles of platelet subsets in health and disease. © 2021 Wiley Periodicals LLC. Basic Protocol: Platelet immunophenotyping by high-dimensional mass cytometry Support Protocol: Data preprocessing.

Platelet Receptor Activity for Predicting Survival in Patients with Intracranial Bleeding

Blood coagulation disorders in patients with intracranial bleeding as a result of head injuries or ruptured aneurysms are a diagnostic and therapeutic problem and appropriate assessments are needed to limit CNS damage and to implement preventive measures. The aim of the study was to monitor changes in platelet aggregation and to assess the importance of platelet dysfunction for predicting survival. Platelet receptor function analysis was performed using the agonists arachidonic acid (ASPI), adenosine diphosphate (ADP), collagen (COL), thrombin receptor activating protein (TRAP), ristocetin (RISTO) upon admission to the ICU and on days 2, 3, and 5. On admission, the ASPI, ADP, COL, TRAP, and RISTO tests indicated there was reduced platelet aggregation, despite there being a normal platelet count. In ‘Non-survivors’, the platelet response to all agonists was suppressed throughout the study period, while in ‘Survivors’ it improved. Measuring platelet function in ICU patients with intracranial bleeding is a strong predictor related to outcome: patients with impaired platelet aggregation had a lower 28-day survival rate compared to patients with normal platelet aggregation (log-rank test p = 0.014). The results indicated that measuring platelet aggregation can be helpful in the early detection, diagnosis, and treatment of bleeding disorders.

Analysis of individualized antiplatelet therapy for patients of acute coronary syndrome after percutaneous coronary intervention under the guidance of platelet function: A one-center retrospective cohort study

There is controversy in clinical application of antiplatelet drugs by monitoring platelet function. Therefore, we explored whether early and dynamic medication could bring better clinical outcomes for patients under the guidance of platelet function tests (PFT).In this retrospective cohort study, we analyzed the prognostic events of 1550 patients with acute coronary syndrome (ACS) at Tianjin People's Hospital in China. They received dual antiplatelet therapy (DAPT) after percutaneous coronary intervention (PCI) from January 2017 to December 2018. The primary endpoint was based on the Bleeding Academic Research Consortium (BARC) 3 or 5 major bleeding. Secondary endpoints included MACCE (all-cause death, nonfatal myocardial infarction, stroke, stent thrombosis, and unplanned target vessel reconstruction) and BARC 1 to 2 minor bleeding. The endpoint events within 1 year after PCI were recorded. Patients were divided into a guided group and a control group according to the drug adjustment by PFT results. After the propensity scores matched, the end points of 2 groups were compared, and subgroup analysis was performed on major bleeding events.After propensity score matching, there were 511 cases in the guided group and the control group, respectively. The primary endpoint events occurred in 10 patients (1.96%) in the guided group and 23 patients (4.5%) in the control group (HR: 0.45; 95% CI, 0.21-0.95; P = .037). After the guided group adjusted drug doses, the risk of major bleeding was lower than standard DAPT of the control group. Although some patients in the guided group reduced doses earlier, the incidence of MACCE events did not increase in the guided group compared with the control group (4.89% vs 6.07%; P = .41). There was no statistical difference in BARC 1 to 2 minor bleeding (P = .22). Subgroup analysis showed that PFT was more effective in patients with diabetes and multivessel disease.Early observation of dynamic PFT in ACS patients after PCI can guide individualized antiplatelet therapy to reduce the risk of major bleeding without increasing the risk of ischemia.

Platelet Phenotyping and Function Testing in Thrombocytopenia

Patients who suffer from inherited or acquired thrombocytopenia can be also affected by platelet function defects, which potentially increase the risk of severe and life-threatening bleeding complications. A plethora of tests and assays for platelet phenotyping and function analysis are available, which are, in part, feasible in clinical practice due to adequate point-of-care qualities. However, most of them are time-consuming, require experienced and skilled personnel for platelet handling and processing, and are therefore well-established only in specialized laboratories. This review summarizes major indications, methods/assays for platelet phenotyping, and in vitro function testing in blood samples with reduced platelet count in relation to their clinical practicability. In addition, the diagnostic significance, difficulties, and challenges of selected tests to evaluate the hemostatic capacity and specific defects of platelets with reduced number are addressed.

Good Platelets Gone Bad: The Effects of Trauma Patient Plasma on Healthy Platelet Aggregation

BACKGROUND

Altered postinjury platelet behavior is recognized in the pathophysiology of trauma-induced coagulopathy (TIC), but the mechanisms remain largely undefined. Studies suggest that soluble factors released by injury may inhibit signaling pathways and induce structural changes in circulating platelets. Given this, we sought to examine the impact of treating healthy platelets with plasma from injured patients. We hypothesized that healthy platelets treated ex-vivo with plasma from injured patients with shock would impair platelet aggregation, while treatment with plasma from injured patients with significant injury burden, but without shock, would enhance platelet aggregation.

METHODS

Plasma samples were isolated from injured patients (pretransfusion) and healthy donors at a Level I trauma center and stored at -80°C. Plasma samples from four separate patients in each of the following stratified clinical groups were used: mild injury/no shock (injury severity score [ISS] 2-15, base excess [BE]>-6), mild injury/with shock (ISS 2-15, BE≤-6), severe injury/no shock (ISS>25, BE>-6), severe injury/with shock (ISS>25, BE≤-6), minimal injury (ISS 0/1, BE>-6), and healthy. Platelets were isolated from three healthy adult males and were treated with plasma for 30 min. Aggregation was stimulated with a thrombin receptor agonist and measured via multiple-electrode platelet aggregometry. Data were normalized to HEPES Tyrode's (HT) buffer-only treated platelets. Associations of plasma treatment groups with platelet aggregation measures were tested with Mann-Whitney U tests.

RESULTS

Platelets treated with plasma from patients with shock (regardless of degree of injury) had significantly impaired thrombin-stimulated aggregation compared with platelets treated with plasma from patients without shock (P = 0.002). Conversely, platelets treated with plasma from patients with severe injury, but without shock, had amplified thrombin-stimulated aggregation (P = 0.030).

CONCLUSION

Shock-mediated soluble factors impair platelet aggregation, and tissue injury-mediated soluble factors amplify platelet aggregation. Future characterization of these soluble factors will support development of novel treatments of TIC.

A microchip flow-chamber assay screens congenital primary hemostasis disorders

BACKGROUND

Von Willebrand disease (VWD) and platelet function disorders (PFDs) are congenital bleeding disorders caused by primary hemostasis defects. Platelet function tests are time-consuming and require considerable amounts of blood sample, and there have been no easy-to-use assays for assessing platelet function quickly and sensitively. We report the usefulness of a microchip flow-chamber system (T-TAS^® ) for detecting and/or predicting clinical severity in patients with VWD type 1 and type 2N and platelet storage pool disease. Here, we developed an application of a screening assay for primary hemostasis disorders.

METHODS

Microchips coated with collagen (PL-chip) and collagen/thromboplastin (AR-chip) were utilized to evaluate platelet thrombus formation (PTF) at high shear and fibrin-rich PTF at low shear, respectively, in whole blood samples from 22 patients with VWD (16 type 2A, four type 2B, two type 3) and four patients with PFDs (two BSS, two Glanzmann thrombasthenia). The time-to-increase by 10 kPa (T₁₀ ) was calculated from flow pressure curves. Also, whole blood-induced platelet aggregation was assessed using Multiplate^® analysis.

RESULTS

PL-chip T₁₀ values ≥10 min successfully distinguished patients with all types of VWD and PFDs from healthy controls, irrespective of age, bleeding scores, and von Willebrand factor levels. However, AR-chip assay incompletely distinguished between type 2A patients and healthy ones. Multiplate analysis permitted screening of PFDs and type 3 VWD, but values in type 2A partially overlapped with those in controls. PL-chip assay did not reflect the clinical severity in these patients.

CONCLUSIONS

T-TAS with PL-chip could be a quick screening tool for congenital primary hemostasis disorder, VWD, and PFDs.

The routine use of platelet function tests in elective coronary artery bypass grafting: A prospective observational trial

BACKGROUND

Preoperative use of platelet function tests contributes to the decrease of re-intervention rate due to bleeding and the necessity of transfusion in coronary artery bypass grafting (CABG) patients. The aim was to investigate the predictive value and to justify routine preoperative use of multiple electrode aggregometry in these patients.

METHODS

A prospective observational trial which included 416 consecutive patients subjected to elective isolated CABG was conducted. The Multiplate® test was used to assess platelet function. Platelet function test results, postoperative blood loss, and transfusion requirements were compared between high and low bleeding risk patients. Receiver operating characteristic analysis was performed to assess the sensitivity and specificity of the arachidonic acid (ASPI) and adenosine di-phosphate high sensitive (ADPHS) tests.

RESULTS

ADPHS and ASPI test results significantly predicted total bleeding > 1000 ml (AUC, 0.685, p < .001; 0.695, p = .039). Sensitivity and specificity were 62.9% and 40.0%, for ADPHS ≤602, and 70.8% and 41.8%, for ASPI ≤ 453. The sensitivity and specificity of cut-off values recommended by the manufacturer were 84.2% and 40.0% for ADPHS ≤ 500, while for ASPI < 600 the values were 54.7% and 62.2%. More platelets and cryoprecipitate were transfused in patients with ADPHS ≤ 602.5 (p < .001; p = .035). Patients with ADPHS ≤ 500 had a higher rate of red blood count, platelet and cryoprecipitate transfusion (p<.001p<.001; p = .013). The manufacturer's ASPI test cut-off values showed no statistically significant prediction for a higher transfusion rate.

CONCLUSION

Preoperative platelet function tests should be conducted systematically for all elective CABG patients who were on dual antiplatelet therapy after adjusting test cut-off values for each population.

Lights and Shadows of Platelet Function Tests to Guide the Best Therapeutic Approach

The key role of platelets in pathophysiology of Acute Coronary Syndromes (ACS) has been well recognized. Platelet activation and aggregation, together with tissue factor-pathway activation, lead to acute thrombus formation in the coronary vessels at sites of plaque rupture. Thus, antiplatelet therapy with drugs able to interfere with platelet activation/aggregation represents a cornerstone of ACS treatment in intensive care units and catheterisation labs. Several observational studies have described that residual high platelet reactivity, despite antiplatelet therapy, is associated with increased risk of nonfatal Myocardial Infarction (MI), definite/probable stent thrombosis and cardiovascular mortality. Thus, assessment of platelet function with reliable and reproducible platelet function tests might be crucial to identify patients at high risk of thrombosis or not responding to ongoing antiplatelet strategies. However, despite this promising background, some randomized clinical trials have failed to demonstrate improvement in outcomes when using platelet function tests for clinical decision-making. This review, after describing platelet biology and pathophysiology of ACS, briefly considers the drugs currently approved for use in patients with ACS or treated by the percutaneous coronary intervention (PCI). Finally, we provide an updated overview of the current methods to evaluate platelet reactivity in the clinical setting of ACS illustrating their potential advantages/limitations in current clinical practice.

The role of platelets in bleeding in patients with thrombocytopenia and hematological disease

This review evaluates the role of platelets in bleeding risk among patients with hematological disease and thrombocytopenia. Platelets are pivotal in primary hemostasis, and possess non-hemostatic properties involved in angiogenesis, tissue repair, inflammation and metastatis. Also, platelets safeguard vascular integrity in inflamed vessels. Overall, bleeding risk depends on the underlying disease, and patients with cancer and platelet count <6-10 × 109/L have a markedly increased bleeding risk, while the platelet count does not correlate with bleeding risk at higher platelet counts. Other factors might affect platelet properties and thus bleeding risk, for example, drugs, low hematocrit, coagulation system impairments or transfusion of dysfunctional donor platelets. For patients with leukemia and immune thrombocytopenia, reduced platelet activation, platelet aggregation, or thrombopoiesis, reflected by the reduced presence of reticulated platelets, are associated with bleeding phenotype. However, mechanistic insight into the cause of reduced platelet function in different thrombocytopenic conditions is sparse, except for some inherited platelet disorders. Promising tools for platelet function studies in thrombocytopenia are flow cytometry and biomarker studies on platelet constituents. An important message from this current paper is that bleeding risk assessment must be tailored to specific patient populations and cannot be applied broadly to all patients with thrombocytopenia.

Optimized tool for evaluation of platelet function measured by impedance aggregometry

Platelet aggregation measured by impedance aggregometry is highly dependent on platelet count. We previously developed a tool to interpret impedance aggregometry based on the strong linear correlation between platelet counts and platelet aggregation at reduced platelet counts. The present study aimed to optimize the tool by expanding the model to include normal platelet counts. We combined data from three previous studies on 266 healthy individuals measuring impedance aggregometry with four agonists (collagen, adenosine diphosphate, thrombin receptor activating peptide-6, and ristocetin). Reduced platelet counts were established in vitro. The investigated platelet counts ranged from 26-425x10⁹/L. A positive linear correlation was found between platelet counts and platelet aggregation across normal and reduced platelet counts (all p-values <0.001). We established 95% prediction intervals for healthy platelet aggregation in relation to platelet count. The new expanded model serves as an optimized tool for evaluation of platelet aggregation at normal and reduced platelet counts.

The Influence of Prostaglandin E1 and Use of Inhibitor Percentage on the Correlation between the Multiplate and VerifyNow in Patients on Dual Antiplatelet Therapy

Platelet function tests (PFT), such as the Multiple Electrode Analyzer (Multiplate) and VerifyNow, show little concordance in patients using antiplatelet drugs. A major difference between these tests is the use of prostaglandin E1 (PGE1) to inhibit P2Y1-platelet-receptor activation in VerifyNow and is proposed to be of influence in the discrepancy between these tests. We aimed to investigate whether the presence of PGE1 could provide an explanation for the moderate correlation and concordance between Multiplate and VerifyNow by adding PGE1 to the Multiplate ADP assay, also known as the ADP-high sensitivity (ADP-HS) assay. We also aimed to investigate whether the difference in baseline platelet function as measured by the VerifyNow and Multiplate could (partly) explain the moderate correlation between the tests, by plotting ADP assay results against baseline function as measured by the corresponding device, which is expressed as the 'inhibitor percentage.' Fifty-one patients who underwent percutaneous coronary intervention (PCI) received dual antiplatelet therapy and were considered to have a high risk of ischemic or bleeding complications were included. The addition of 20 µl PGE1 in the Multiplate resulted in a significant reduction in Arbitrary Aggregation Units, but did not improve correlation with the VerifyNow. The correlation between VerifyNow and Multiplate inhibitor percentage was moderate. Based on these results, we concluded that neither PGE1 nor the calculation of the inhibitor percentage greatly influenced the correlation between PFTs.

Sensitivity of Viscoelastic Tests to Platelet Function

Viscoelastic tests provide a dynamic assessment of coagulation, by exploring the time to clot formation and the clot strength. Using specific activators or inhibitors, additional factors can be explored, like the fibrinogen contribution to clot strength. Since the early days, various attempts have been done to measure platelet function with viscoelastic test. In general, the difference between the maximum clot strength and the fibrinogen contribution is considered an index of platelet contribution. However, this parameter does not clearly split platelet count from function; additionally, the extensive thrombin generation of standard activated viscoelastic tests activates platelet through the protease activated receptors, bypassing the other pathways. For this reason, standard viscoelastic tests cannot be used to assess platelet reactivity under the effects of aspirin or P2Y12 inhibitors. To overcome this limitation, a specific test was developed (thromboelastography platelet mapping). This test has been compared with the gold standard of light transmission aggregometry and with other point-of-care tests, with conflicting results. In general, the use of viscoelastic tests to assess the effects of antiplatelet agents is still limited. Conversely, platelet contribution to clot strength in the setting of coagulopathic bleeding is considered an important parameter to trigger platelet transfusion or desmopressin.

An in vitro model to mimic the thrombotic occlusion of small vessels in catastrophic antiphospholipid syndrome (CAPS)

Platelet activation and decrease in platelet count characterize the development of the most feared form of antiphospholipid syndrome (APS), i.e. catastrophic APS (CAPS). We aimed to assess if immuno-affinity purified anti-β2-glycoprotein I (aβ2GPI) antibodies enhance platelet activation inducing a significant flow obstruction in a platelet function analyzer (PFA). Affinity purified aβ2GPI antibodies were obtained from 13 triple positive patients with a strong lupus anticoagulant (LA) and high titers of IgG anticardiolipin antibodies (aCL) and IgG aβ2GPI. Platelet activation stimulated by adenosine diphosphate (ADP) in the presence or absence of aβ2GPI was measured by the expression of P-selectin on platelet surface using flow cytometry. P-selectin expression remained close to baseline when normal whole blood was incubated with aβ2GPI alone. When stimulated using aβ2GPI combined with ADP, P-selectin expression (28.42 ± 5.15% vs. 20.98 ± 3.94%, p = 0.0076) was significantly higher than ADP alone. Closure time of normal whole blood passed through the PFA was significantly shorter using affinity purified aβ2GPI than control IgG both in Col/ADP (160.1 ± 62.1 s vs. 218.6 ± 43.8 s; p = 0.021) and Col/EPI cartridges (149.5 ± 26.7 s vs. 186.9 ± 45.5 s; p = 0.030). Thus, platelet activation is enhanced by aβ2GPI antibodies with a consequent premature closure in a PFA, possibly resembling that in microcirculation in patients with CAPS.

Platelet preparation for function testing in the laboratory and clinic: Historical and practical aspects

Laboratory tests of platelet function are instrumental in studying platelet physiology and inherited or acquired platelet abnormalities. Light transmission aggregometry, developed in the early 1960s, is still considered the gold standard for the identification and diagnosis of platelet function disorders. Since then, novel techniques have been developed, including flow-based assays and flow cytometry. In this tutorial, we describe the basic methodologies for the preparation of citrated platelet-rich plasma and washed platelet suspensions and discuss their respective advantages and limitations as well as important factors to consider to perform high-quality tests of platelet function. In addition, the methodologies of the main platelet function tests (light transmission aggregation, flow-based assays, and flow cytometric assays) are described, and their respective strengths and limitations are discussed to assess various aspects of platelet biology.

Platelet Function During Extracorporeal Membrane Oxygenation in Adult Patients

Objective: Hemorrhagic and thromboembolic complications are common during support with extracorporeal membrane oxygenation (ECMO). As platelets play a pivotal role in hemostasis, we aimed to clarify how ECMO support affects platelet function.

Methods: We included 33 adult patients undergoing ECMO support at a tertiary ECMO referral center at Aarhus University Hospital, Denmark. Blood samples were collected on the first morning following ECMO initiation, and subsequently every morning until the 7th (±1) day. Platelet aggregation was evaluated by whole blood impedance aggregometry (Multiplate^® Analyzer) using adenosine diphosphate (ADPtest), arachidonic acid (ASPItest), and thrombin-receptor-agonist-peptide-6 (TRAPtest) as agonists. A new model was applied, taking platelet count into consideration in interpretation of impedance aggregometry analyses. On the 1st and 3rd day, platelet activation was assessed by flow cytometry (Navios) using collagen-related peptide, ADP, TRAP, and arachidonic acid as agonists.

Results: Blood samples from all 33 patients were analyzed on day 1 of ECMO support; 24 patients were still receiving ECMO and analyzed on day 3; 12 patients were analyzed on day 7 (±1). After ECMO initiation, platelet counts decreased significantly (p < 0.002) and remained low during ECMO support. ECMO patients demonstrated significantly reduced platelet aggregation on day 1 compared with healthy controls (all p < 0.001). However, when taking platelet count into consideration, platelet aggregation relative to platelet count did not differ from healthy controls. Flow cytometry analyses demonstrated impaired platelet activation in ECMO patients on day 1 compared with healthy controls (all p < 0.03). No substantial difference was found in platelet activation from day 1 to day 3 on ECMO support.

Conclusions: Employing impedance aggregometry and flow cytometry, we found both impaired platelet aggregation and decreased platelet activation on day 1 of ECMO support compared with healthy controls. However, platelet aggregation was not impaired, when interpreted relative to the low platelet counts. Furthermore, levels of bound fibrinogen, on the surface of activated platelets in ECMO patients, were higher than in healthy controls. Together, these findings suggestively oppose that platelets are universally impaired during ECMO support. No marked difference in activation from day 1 to day 3 was seen during ECMO support.

[Reference values of platelet aggregometry in healthy subjects.]

In this article, we set forth the average values and reference intervals of platelet aggregation in practically healthy individuals on the AggRAM optical aggregometer. The reference intervals of platelet aggregation activity with 5 µg/ml adenosine-5`-diphosphate and the area under the aggregation curve were 67,4-92,5% and 54,5-85,3; the reference intervals of platelet activity with 10 µg/ml adenosine-5`-diphosphate and the area under the aggregation curve were 76,8-97,2%% and 68,8-90,4. The obtained values of indicators can be used as reference in the clinical diagnostic laboratory of the University Hospital of Semey State Medical University.

Evaluation of Platelet Parameters in Children with Autism Spectrum Disorder: Elongated Collagen-Adenosine Diphosphate and Collagen-Epinephrine Closure Times

Changes related to the serotonin system play a key role in the etiology of autism spectrum disorder (ASD). Although we know that platelets are associated with the serotonin system, their relation to ASD has not yet been elucidated. In this study, we aim to investigate platelet parameters in children with ASD. Forty patients with ASD according to Diagnostic and Statistical Manual of Mental Disorders 5 (DSM-5) and 30 healthy controls were included in the study. A complete blood count was done to measure parameters relating to platelet morphology. Moreover, prothrombin time (PT) and activated partial thromboplastin time (aPTT) were evaluated. Lastly, platelet functions were assessed with a platelet functions analyzer 100 (PFA-100) device by measuring collagen-ADP and collagen-epinephrine (EPI) closure times. There was not a significant difference between the groups in terms of platelet count, mean platelet volume (MPV), platelet distribution width, plateletcrit, PT, or aPTT parameters for ASD patients when compared to the control group (P > 0.05). However, MPV in severe ASD, as quantified by the Childhood Autism Rating Scale, was found to be significantly lower when compared to mild to moderate ASD (P = 0.047). Moreover, in terms of platelet functions, the elongation in collagen-ADP and collagen-EPI closure times were significantly higher for the ASD group (P = 0.044). These results may suggest an impairment in platelet functions rather than in platelet morphology for children with ASD. Considering these results, further investigation of thrombocyte functions in the ASD may lead to a better understanding of the pathogenesis of ASD and to the development of our limited knowledge of this disorder. Autism Res 2019, 12: 1069-1076. © 2019 International Society for Autism Research, Wiley Periodicals, Inc. LAY SUMMARY: Serotonin is a chemical that is found in brain as wells as in blood cells that function in blood clotting in the human body. There are problems related to serotonin in brains of people who have autism. Thus, blood clotting cells may also be affected in people who have autism. In this study, we compare blood clotting functions of children with autism with that of healthy controls.

Diagnostic utility of the ISTH bleeding assessment tool in patients with suspected platelet function disorders

Essentials The utility of bleeding assessment tools regarding platelet function disorders is still elusive. We studied consecutive patients in a prospective cohort study in a tertiary hospital. Substantially higher scorings were observed in patients with platelet function disorders. Bleeding assessment tools might provide a useful screening tool.

BACKGROUND

Bleeding assessment tools (BATs) have been widely implemented in the evaluation of patients with suspected bleeding disorders. However, diagnostic BAT utility regarding platelet function disorders is still elusive.

AIM

We aimed to assess the diagnostic value of the International Society on Thrombosis and Haemostasis BAT (ISTH-BAT) for platelet function disorders in clinical practice.

METHODS

The clinical characteristics and laboratory data of all consecutive patients with a suspected bleeding disorder referred between January 2012 and March 2017 to an outpatient unit of a university hospital were prospectively collected. The diagnostic evaluation was performed according to current recommendations following a prespecified protocol and platelet function was tested using light transmission aggregometry as well as flow cytometry.

RESULTS

Five hundred and fifty-five patients were assessed; 66.9% were female, median age was 43.7 years (interquartile range [IQR] 29.3, 61.7). Confirmed platelet function disorder was diagnosed in 54 patients (9.7%), possible platelet function disorder in 64 patients (11.5%), and other disorders in 170 patients (30.6%). Median scoring of the ISTH-BAT was 2 in patients without a bleeding disorder (IQR 1, 3), 4 in patients with a possible platelet function disorder (2, 7), and 7 in patients with confirmed platelet function disorder (5, 9). Area under the receiver operating characteristic curve (the area under the curve [AUC]) was 0.75 (95% CI 0.70, 0.80).

CONCLUSIONS

Presence of a platelet function disorder was associated with substantially higher BAT scorings compared to patients without. Our data suggest that the ISTH-BAT provides a useful screening tool for patients with suspected platelet function disorders.

Multiple electrode aggregometry and thromboelastography in thrombocytopenic patients with haematological malignancies

BACKGROUND

In thrombocytopenic patients better assessment of bleeding risk than that provided by platelet count alone is required. Multiplate® aggregometry and thromboelastography (TEG) could be used, but information on their role in such patients is limited. The primary aim of this study was to investigate the feasibility of Multiplate® analyses in patients with haematological malignancies. A secondary aim was to explore whether a multiple logistic regression model combining Multiplate®, TEG, clinical and laboratory variables was associated with risk of bleeding.

MATERIALS AND METHODS

This was an exploratory, prospective observational study of thrombocytopenic patients with haematological malignancies. Total platelet count (TPC), white blood cell count, C-reactive protein (CRP) level, temperature and bleeding status were recorded daily. TEG and Multiplate® analyses with four agonists were performed on weekdays.

RESULTS

Ten patients were enrolled into the study. The median number of days in a study period was 21. Bleeding was observed on 64 of 298 study days. TPC <20×109/L and <10×109/L occurred on 119 and 25 days, respectively. When TPC was <33×109/L, many samples showed no aggregation, regardless of bleeding status. Despite this, the odds of World Health Organization (WHO) grade 2 bleeding decreased significantly as aggregation increased and Multiplate® had a negative predictive value (NPV) of 96% and a positive predictive value (PPV) of 19% for significant bleeding. In the multiple logistic regression model collagen-activated Multiplate® aggregation, TEG angle, TEG reaction time and CRP significantly affected the odds of WHO grade 2 bleeding. The combined model had a NPV of 99% and a PPV of 19%.

DISCUSSION

Our findings suggest that the markers of platelet function and haemostasis provided by Multiplate® aggregometry and TEG may add information to support prediction of bleeding, although platelet count still remains the most accessible analysis for routine testing.

Observational Study of Platelet Reactivity in Patients Presenting With ST-Segment Elevation Myocardial Infarction Due to Coronary Stent Thrombosis Undergoing Primary Percutaneous Coronary Intervention: Results From the European PREvention of Stent Thrombosis by an Interdisciplinary Global European Effort Registry

OBJECTIVES

High platelet reactivity (HPR) was studied in patients presenting with ST-segment elevation myocardial infarction (STEMI) due to stent thrombosis (ST) undergoing immediate percutaneous coronary intervention (PCI).

BACKGROUND

HPR on P2Y₁₂ inhibitors (HPR-ADP) is frequently observed in stable patients who have experienced ST. The HPR rates in patients presenting with ST for immediate PCI are unknown.

METHODS

Consecutive patients presenting with definite ST were included in a multicenter ST registry. Platelet reactivity was measured before immediate PCI with the VerifyNow P2Y₁₂ or Aspirin assay.

RESULTS

Platelet reactivity was measured in 129 ST patients presenting with STEMI undergoing immediate PCI. HPR-ADP was observed in 76% of the patients, and HPR on aspirin (HPR-AA) was observed in 13% of the patients. HPR rates were similar in patients who were on maintenance P2Y₁₂ inhibitor or aspirin since stent placement versus those without these medications. In addition, HPR-ADP was similar in patients loaded with a P2Y₁₂ inhibitor shortly before immediate PCI versus those who were not. In contrast, HPR-AA trended to be lower in patients loaded with aspirin as compared with those not loaded.

CONCLUSIONS

Approximately 3 out of 4 ST patients with STEMI undergoing immediate PCI had HPR-ADP, and 13% had HPR-AA. Whether patients were on maintenance antiplatelet therapy while developing ST or loaded with P2Y₁₂ inhibitors shortly before undergoing immediate PCI had no influence on the HPR rates. This raises concerns that the majority of patients with ST have suboptimal platelet inhibition undergoing immediate PCI.

Intraoperative infusion of noradrenaline improves platelet aggregation in patients undergoing coronary artery bypass grafting: a randomized controlled trial

Essentials Strategies to improve platelet function may reduce excessive bleeding during cardiac surgery. Patients were randomized to standard care or standard care + noradrenaline infusion. Low-dose noradrenaline improved intraoperative platelet aggregation and clot formation. Noradrenaline may be considered to improve intraoperative hemostasis during cardiac surgery. SUMMARY: Background New approaches to prevent bleeding complications during cardiac surgery are needed. Objective To investigate if noradrenaline (NA) enhances platelet aggregation in patients undergoing coronary artery bypass grafting (CABG). Patients/Methods Twenty-four patients undergoing coronary artery bypass grafting (CABG) were included in a prospective parallel-group randomized study. All patients but one were treated with acetylsalicylic acid (ASA). In the treatment group (n = 12), mean arterial blood pressure (MAP) was maintained at pre-induction levels by NA infusion. In the control group (n = 12), NA was administered only if MAP decreased below 60 mmHg. Platelet aggregation (impedance aggregometry with ADP, arachidonic acid [AA] and thrombin-receptor activating peptide [TRAP] as initiators) and clot formation (clotting time, clot formation time and maximum clot firmness by EXTEM, INTEM and FIBTEM tests with thromboelastometry) were assessed before and 50 min after anesthesia induction (before cardiopulmonary bypass was initiated). Results All patients in the treatment group received NA (median dose after 50 min 0.09 (range 0-0.26) μg kg-1  min-1 ). Four patients in the control group also received NA (0.03-0.12 μg kg-1  min-1 ). There were differences between the treatment group and the control group in ADP- and AA-induced aggregation changes (ADP, +16 [25th-75th percentiles, 5-26] vs. -7 [-19 to -1] U; AA, +12 [-4 to 16] vs. -9 [-13 to 1] U). INTEM maximum clot firmness increased in the treatment group but not in the control group. Conclusion Infusion of clinically relevant doses of NA enhanced platelet aggregation and clot firmness in ASA-treated CABG patients. NA infusion is hence a potential new method to acutely improve platelet reactivity in patients on antiplatelet therapy undergoing surgery.

Platelet function testing at low platelet counts: When can you trust your analysis?

BACKGROUND

Although flow cytometry is often brought forward as a preferable method in the setting of thrombocytopenia, the relative effects of low sample counts on results from flow cytometry-based platelet function testing (FC-PFT) in comparison with light transmission aggregometry (LTA) and multiple electrode aggregometry (MEA) has not been reported.

OBJECTIVES

To compare the effects of different sample platelet counts (10, 50, 100, and 200 × 109 L-1) on platelet activation measured with FC-PFT, LTA, and MEA using the same anticoagulant and agonist concentrations as for the commercial MEA test.

METHODS

Platelets were stimulated with two commonly used platelet agonists (ADP [6.5 μmol L-1] and PAR1-AP [TRAP, 32 μmol L-1]). The specified sample platelet counts were obtained by combining platelet-rich and platelet poor hirudinized plasma in different proportions with or without red blood cells.

RESULTS

For FC, P-selectin exposure and PAC-1 binding was reduced at 10 × 109 L-1 after stimulation with PAR1-AP (by approximately 20% and 50%, respectively), but remained relatively unchanged when ADP was used as agonist (n = 9). The platelet count-dependent effects observed with PAR1-AP were eliminated when samples were pre-incubated with apyrase, implying that reduced purinergic signaling was the main underlying factor (n = 5). Both aggregometry-based PFTs showed a 50% reduction at 50 × 109 L-1 and more than 80% reduction at 10 × 109 L-1, irrespective of agonist used (n = 7).

CONCLUSIONS

Although FC-PFT is generally preferable to aggregometry-based PFTs in situations with low sample platelet counts, a careful optimization of experimental parameters is still required in order to eliminate platelet count-related effects.

Arachidonic acid causes lysis of blood cells and ADP-dependent platelet activation responses in platelet function tests

The use of arachidonic acid (AA) to stimulate platelets is considered as a specific approach to study aspirin treatment efficacy. However, very high concentrations of AA are used, and it has been previously reported that AA can induce cell lysis in other settings. Several clinical studies have reported decreased responses to AA in whole blood tests in the presence of clopidogrel. Our aim was to investigate whether unspecific effects contribute to AA-induced aggregation and platelet activation in light transmission aggregometry (LTA) in platelet-rich plasma (PRP), and in assays using whole blood, multiple electrode aggregometry (MEA, Multiplate®), and flow cytometry. We report that cell lysis, especially of red blood cells, does occur at concentrations of AA used in the clinical tests and that ADP is very important for the AA-induced platelet activation responses. In flow cytometry, very limited platelet activation was detected before reaching AA concentrations in the millimolar range, where cell lysis also occurred, making it problematic to develop a reliable flow cytometry assay using AA as reagent. We conclude that cell lysis and ADP release contribute to AA-induced platelet responses, most markedly in whole blood assays. This finding could potentially explain some differences between studies comparing methods using whole blood and PRP and also how clopidogrel treatment could influence AA-induced aggregation results in previously published studies. Our findings highlight some issues with AA as reagent for platelet activation, which also have an impact on how platelet activation assays using AA should be interpreted.

Investigation of the contribution of an underlying platelet defect in women with unexplained heavy menstrual bleeding

Heavy menstrual bleeding (HMB) is often undiagnosed in women and can cause discomfort and distress. A haemostatic cause for excessive bleeding is often not routinely investigated and can lead to hysterectomy at an early age. A prospective cohort study was carried out to determine whether certain patients with unexplained HMB have an underlying platelet function defect (PFD). The Genotyping and Phenotyping of Platelets (GAPP) study recruited 175 women with HMB and 44 unrelated volunteers from 25 Haemophilia Centres across the UK, and a tertiary gynaecology service. Bleeding history was assessed using the International Society on Thrombosis and Haemostasis Bleeding Assessment Tool (ISTH-BAT). Platelet count, platelet size, haemoglobin and mean corpuscular volume were measured in whole blood using the Sysmex XN-1000 Haematology Analyzer. Platelet function testing using lumiaggregometry and flow cytometry was performed in patients included in this study. A PFD was identified in 47% (82/175) of patients with HMB. Cutaneous bleeding was the most frequent additional bleeding symptom (89% in PFD and 83% with no PFD). Whole blood platelet count was significantly lower (P < 0.0001) between the PFD group and no PFD group. The prevalence of anaemia did not differ between patients and healthy volunteers. Clinical evaluation alone is insufficient to determine presence of an underlying PFD in patients with HMB. Platelet function tests may be considered and clinical guidelines may include them in their algorithms. An appropriate diagnosis and subsequent tailored management of HMB may prevent unnecessary surgery and help manage future haemostatic challenges.

Hemostatic abnormalities in patients with Ehlers-Danlos syndrome

Essentials Ehlers-Danlos Syndrome (EDS) is a rare heterogeneous group of inherited collagen disorders. A cohort of EDS patients was investigated for bleeding tendency and hemostatic abnormalities. EDS is associated with an increased risk of bleeding. EDS patients have platelet function abnormalities, whose severity correlates with bleeding risk. SUMMARY: Background Ehlers-Danlos syndrome (EDS) includes a heterogeneous group of connective tissue disorders affecting skin, bones, vessels, and other organs. Patients with EDS have an increased risk of bleeding, but a comprehensive study of hemostasis in EDS patients is lacking. Objective To investigate the bleeding tendency of a cohort of patients with EDS by using the Bleeding Assessment Tool of the ISTH, the bleeding severity score (BSS). Methods The BSS was defined as abnormal when it was ≥ 4 in men and ≥ 6 in women. Patients with a bleeding tendency were compared with those without in terms of type and number of hemostatic abnormalities. Results Fifty-nine of 141 patients with EDS (41.7%) had an abnormal BSS. Prothrombin time and activated partial thromboplastin time were slightly prolonged in 10 patients (7.1%) because of mild coagulation factor deficiencies, which were not responsible for the bleeding diathesis. von Willebrand factor antigen, ristocetin cofactor, endogenous thrombin potential and platelet count were normal in all patients. At least one platelet function abnormality was found in 53 patients (90%) with an abnormal BSS and in 64 (78%) with a normal BSS (adjusted odds ratio [OR] 2.55, 95% confidence interval [CI] 0.87-7.48). The risk of bleeding progressively increased with the number of platelet function abnormalities, reaching an OR of 5.19 (95% CI 1.32-20.45) when more than three abnormalities were detected. Conclusions Our results show that nearly half of patients with EDS have an abnormal BSS, which, in 90% of cases, appear, at least in part, to be attributable to platelet function abnormalities. Abnormalities of primary hemostasis may contribute to the risk of bleeding in patients with EDS.

Platelet Function During Extracorporeal Membrane Oxygenation in Adult Patients: A Systematic Review

Background: Hemorrhagic and thromboembolic complications are common during treatment with extracorporeal membrane oxygenation (ECMO), resulting in considerable morbidity and mortality. This emphasizes the clinical relevance of understanding hemostatic changes occurring during ECMO treatment. As platelets are key players in hemostasis, detailed knowledge on how ECMO treatment affects platelet function is of great importance. We therefore aimed to systematically summarize and discuss existing knowledge on platelet function during ECMO treatment in adult patients. Methods: Systematic review complying with the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines. Objectives and methods were specified in a PROSPERO protocol (ID no CRD42018084059). The MEDLINE/PubMed, EMBASE, and Web of Science databases were systematically searched on September 10, 2018. A standardized quality assessment tool was used to assess the risk of bias in included studies. Primary outcome was platelet function during ECMO treatment, measured as platelet adhesion, activation or aggregation. Secondary outcomes were thrombosis, bleeding, and mortality during ECMO treatment. Results: A total of 591 studies were identified, of which seven were eligible for inclusion in the qualitative synthesis. Of these, one study investigated expression of platelet adhesion receptors and found them to be reduced during ECMO treatment; two studies reported a decrease in platelet activation markers during ECMO treatment; and five studies demonstrated reduced platelet aggregation during ECMO treatment. Three studies reported on thrombosis, mortality and/or bleeding during ECMO treatment; no thromboembolic events were reported; all three studies reported frequent bleeding episodes defined on basis of transfusion requirements. An in-hospital mortality of 35-40% and a 30-day mortality of roughly 30% were reported in three different studies. Conclusions: The present systematic review reveals a substantial knowledge gap regarding platelet function during ECMO treatment in adult patients and underscores the demand for more and well-designed studies on this topic. There is suggested evidence of reduced platelet adhesion, decreased platelet activation, and reduced platelet aggregation in adult patients during ECMO treatment. Importantly, platelet aggregation results need to be interpreted in the light of low platelet counts. The associations of platelet function and bleeding and/or thromboembolic complications during ECMO treatment remain to be fully elucidated.

Platelet function after cardiac surgery and its association with severe postoperative bleeding: the PLATFORM study

Platelet dysfunction after cardiac surgery is a determinant of postoperative bleeding. The existing guidelines suggest the use of desmopressin and/or platelet concentrate transfusions in case of platelet dysfunction in bleeding patients, but no cut-off values for platelet activity exist in the literature. The Platelet Function in the Operating Room (PLATFORM) study aims to identify the relationship between platelet function after cardiopulmonary bypass and severe bleeding, finding adequate predictive values of platelet function for severe bleeding. The PLATFORM is a prospective cohort study on 490 adult patients receiving cardiac surgery with cardiopulmonary bypass. Patients received platelet function tests (multiple electrode aggregometry ADPtest and TRAPtest) before surgery and after cardiopulmonary bypass, and routine coagulation tests before surgery and at the arrival in the intensive care unit. The post-cardiopulmonary bypass ADPtest and TRAPtest were significantly (P = 0.001) associated with severe bleeding, as well as the post-cardiopulmonary bypass activated partial thromboplastin time, the international normalized ratio, and the fibrinogen concentration. At a multivariable analysis, the ADPtest (odds ratio 0.962, 95% confidence interval 0.936-0.989, P = 0.005) and the activated partial thromboplastin time (odds ratio 1.097, 95% confidence interval 1.016-1.185, P = 0.017) remained independently associated with severe bleeding. The post-cardiopulmonary bypass ADPtest had the best discrimination, with an area under the curve of 0.712. The best positive predictive value (42%) was found at a cut-off ≤8 U. In conclusion, platelet function tests after cardiopulmonary bypass are significantly associated with postoperative bleeding. However, postoperative bleeding has a multifactorial nature, and the measure of platelet function alone does not provide a high positive predictive value for severe bleeding.

Assessment of whole blood coagulation with a microfluidic dielectric sensor

Essentials ClotChip is a novel microsensor for comprehensive assessment of ex vivo hemostasis. Clinical samples show high sensitivity to detecting the entire hemostatic process. ClotChip readout exhibits distinct information on coagulation factor and platelet abnormalities. ClotChip has potential as a point-of-care platform for comprehensive hemostatic analysis.

SUMMARY

Background Rapid point-of-care (POC) assessment of hemostasis is clinically important in patients with a variety of coagulation factor and platelet defects who have bleeding disorders. Objective To evaluate a novel dielectric microsensor, termed ClotChip, which is based on the electrical technique of dielectric spectroscopy for rapid, comprehensive assessment of whole blood coagulation. Methods The ClotChip is a three-dimensional, parallel-plate, capacitive sensor integrated into a single-use microfluidic channel with miniscule sample volume (< 10 μL). The ClotChip readout is defined as the temporal variation in the real part of dielectric permittivity of whole blood at 1 MHz. Results The ClotChip readout exhibits two distinct parameters, namely, the time to reach a permittivity peak (Tpeak ) and the maximum change in permittivity after the peak (Δεr,max ), which are, respectively, sensitive towards detecting non-cellular (i.e. coagulation factor) and cellular (i.e. platelet) abnormalities in the hemostatic process. We evaluated the performance of ClotChip using clinical blood samples from 15 healthy volunteers and 12 patients suffering from coagulation defects. The ClotChip Tpeak parameter exhibited superior sensitivity at distinguishing coagulation disorders as compared with conventional screening coagulation tests. Moreover, the ClotChip Δεr,max parameter detected platelet function inhibition induced by aspirin and exhibited strong positive correlation with light transmission aggregometry. Conclusions This study demonstrates that ClotChip assesses multiple aspects of the hemostatic process in whole blood on a single disposable cartridge, highlighting its potential as a POC platform for rapid, comprehensive hemostatic analysis.

Adrenaline enhances in vitro platelet activation and aggregation in blood samples from ticagrelor-treated patients

BACKGROUND

Temporarily improved platelet reactivity may reduce the bleeding in patients on antiplatelet therapy who have ongoing bleeding or who are in need of acute surgery. Adrenaline can bind to adrenergic α2A-receptors on platelets and potentially enhance platelet reactivity.

OBJECTIVE

To assess if adrenaline can improve adenosine diphosphate (ADP)-induced platelet aggregation and activation in blood samples from patients on dual antiplatelet therapy with acetylsalicylic acid (ASA) and the ADP-receptor antagonist ticagrelor.

METHODS

Blood samples were collected from a total of forty acute coronary syndrome patients on dual antiplatelet therapy with ASA and ticagrelor. ADP-induced platelet aggregation (by impedance aggregometry) and activation (by flow cytometry) were assessed before and after supplementation with adrenaline and/or platelet concentrate.

RESULTS

Adrenaline supplementation (770 nmol L-1) increased median ADP-induced aggregation from 15 (25-75th percentiles: 10-20) to 26 (18-38) aggregation units. The effect was independent of concomitant platelet supplementation. Adrenaline also increased ADP-induced platelet activation: from 40% (36-54%) to 83% (74-88%) platelets with active fibrinogen receptor (binding PAC-1) and from 13% (7-21%) to 35% (18-50%) P-selectin-expressing platelets.

CONCLUSIONS

Adrenaline potentiated ADP-induced platelet aggregation and activation in blood samples from ticagrelor-treated patients. Adrenaline infusion may be a new method to enhance platelet function in ticagrelor-treated patients who are in need of acute surgery or have ongoing bleeding. In vivo studies are needed to confirm the present results.