Platelet function analyzer (PFA)-100 closure time in the evaluation of platelet disorders and platelet function

Randomized Phase I Trial of the α-Synuclein Antibody Lu AF82422

BACKGROUND

Immunotherapy targeting pathological α-synuclein (α-syn) species is a promising strategy for slowing disease progression in neurodegenerative synucleinopathies, including Parkinson's disease (PD).

OBJECTIVE

The aim was to evaluate the safety, tolerability, pharmacokinetics, and target engagement of ascending doses of Lu AF82422.

METHODS

In this first-in-human study (NCT03611569), healthy participants (18-55 years, cohort A) and patients with PD (40-80 years, Hoehn and Yahr stage ≤3, cohort B) were enrolled in ascending-dose cohorts and randomly assigned to receive single intravenous infusions of Lu AF82422 (cohorts A1-A6: 75, 225, 750, 2250 4500, and 9000 mg, respectively; cohorts B1 and B2: 2250 and 9000 mg, respectively) or placebo. Participants were monitored during a 12-week observational period.

RESULTS

Overall, single intravenous infusions of Lu AF82422 were safe and well tolerated, and no serious adverse events (AE) were observed; the most common AEs were related to the study on lumbar punctures, headache, and common infections. Lu AF82422 concentrations (in plasma and cerebrospinal fluid [CSF]) increased in a dose-proportional manner with no observable differences between cohorts; mean plasma half-life was 700 h. Plasma concentrations of Lu AF82422 had an immediate, concentration-dependent lowering effect on the plasma concentration of free α-syn and on the ratio of free to total α-syn in all cohorts and lowered the free-to-total α-syn ratio in CSF in the high-dose PD cohort.

CONCLUSIONS

The safety and pharmacokinetic profile of Lu AF82422 were appropriate for further clinical development, and results indicated peripheral target engagement. The central target engagement observed in participants with PD indicates that the doses of Lu AF82422 tested may provide CSF concentrations sufficient to target aggregated forms of α-syn. © 2024 H. Lundbeck A/S. Movement Disorders published by Wiley Periodicals LLC on behalf of International Parkinson and Movement Disorder Society.

The evolving knowledge on primary hemostasis in patients with cirrhosis: A comprehensive review

Patients with cirrhosis develop complex alterations in primary hemostasis that include both hypocoagulable and hypercoagulable features. This includes thrombocytopenia, multiple alterations of platelet function, and increased plasma levels of von Willebrand factor. Contrary to the historical view that platelet dysfunction in cirrhosis might be responsible for an increased bleeding tendency, the current theory posits a rebalanced hemostasis in patients with cirrhosis. Severe thrombocytopenia is not indicative of the bleeding risk in patients undergoing invasive procedures and does not dictate per se the need for pre-procedural prophylaxis. A more comprehensive and individualized risk assessment should combine hemostatic impairment, the severity of decompensation and systemic inflammation, and the presence of additional factors that may impair platelet function, such as acute kidney injury and bacterial infections. Although there are multiple, complex alterations of platelet function in cirrhosis, their net effect is not yet fully understood. More investigations evaluating the association between alterations of platelet function and bleeding/thrombosis may improve risk stratification in patients with decompensated cirrhosis. Besides hemostasis, the assessment of von Willebrand factor Ag and ADP-induced, whole-blood platelet aggregation normalized by platelet count (VITRO score and PLT ratio) are promising biomarkers to predict the risk of hepatic decompensation and survival in both compensated and decompensated patients. Further investigations into the in vivo interplay between platelets, circulating blood elements, and endothelial cells may help advance our understanding of cirrhotic coagulopathy. Here, we review the complex changes in platelets and primary hemostasis in cirrhosis and their potential clinical implications.

Platelet function analyzer-200 closure curve analysis and assessment of flow-obstructed samples

BACKGROUND

The Platelet function analyzer-200 can determine the effect of clopidogrel in cats. Flow obstruction is an error that causes uninterpretable results. Closure curves and parameters initial flow rate (IF) and total volume (TV) are displayed by the PFA-200 and may allow interpretation of results in cases of flow obstruction. The primary hemostasis components (PHC) are calculated values that normalize these parameters.

OBJECTIVES

To determine if closure curves and research parameters allow detecting the effect of clopidogrel in cases of flow obstruction.

METHODS

A review of closure curves identified those with flow obstruction and paired analysis that did not. Non-flow-obstructed curves were used to categorize curves with respect to clopidogrel effects. IF, TV, PHC(1), and PHC(2) were evaluated to determine if these could be used to categorize if a sample exhibited the effects of clopidogrel. Curves were visually analyzed, and characteristics identified that were more common with or without the effect of clopidogrel. Visual analysis of curves was performed by blinded observers to determine if a visual analysis was able to predict the effect of clopidogrel.

RESULTS

Analysis of parameters was able to predict closure or non-closure in flow-obstructed curves. TV, PHC(1), and PHC(2) had area under the curve of the receiver operating characteristics of 0.79, 0.79, and 0.87. Visual curve analysis was unable to predict closure, with an average accuracy of only 55%, among three reviewers. Agreement between reviewers was poor (Fleiss' Kappa 0.06).

CONCLUSIONS

Visual curve analysis was unable to determine the effect of clopidogrel in flow-obstructed samples. Numerical parameters were able to detect the effect of clopidogrel with a high degree of accuracy in flow-obstructed samples.

The efficacy of aspirin to inhibit platelet aggregation in patients hospitalised with a severe infection: a multicentre, open-label, randomised controlled trial

Patients with severe infection have an increased risk of cardiovascular events. A possible underlying mechanism is inflammation-induced platelet aggregation. We investigated whether hyperaggregation occurs during infection, and whether aspirin inhibits this. In this multicentre, open-label, randomised controlled trial, patients hospitalised due to acute infection were randomised to receive 10 days of aspirin treatment (80 mg 1dd or 40 mg 2dd) or no intervention (1:1:1 allocation). Measurements were performed during infection (T1; days 1-3), after intervention (T2; day 14) and without infection (T3; day > 90). The primary endpoint was platelet aggregation measured by the Platelet Function Analyzer® closure time (CT), and the secondary outcomes were serum and plasma thromboxane B2 (sTxB2 and pTxB2). Fifty-four patients (28 females) were included between January 2018 and December 2020. CT was 18% (95%CI 6;32) higher at T3 compared with T1 in the control group (n = 16), whereas sTxB2 and pTxB2 did not differ. Aspirin prolonged CT with 100% (95%CI 77; 127) from T1 to T2 in the intervention group (n = 38), while it increased with only 12% (95%CI 1;25) in controls. sTxB2 decreased with 95% (95%CI - 97; - 92) from T1 to T2, while it increased in the control group. pTxB2 was not affected compared with controls. Platelet aggregation is increased during severe infection, and this can be inhibited by aspirin. Optimisation of the treatment regimen may further diminish the persisting pTxB2 levels that point towards remaining platelet activity. This trial was registered on 13 April 2017 at EudraCT (2016-004303-32).

Efficacy and Safety Analysis of Combination Therapy Consisting of Intravenous Immunoglobulin and Corticosteroids versus Respective Monotherapies in the Treatment of Relapsed ITP in Adults

Objective  In this study, we aimed to evaluate the efficacy and safety of combination therapy, consisting of intravenous immunoglobulin (IVIg) and corticosteroids, in comparison to respective monotherapies in the treatment of relapsed immune thrombocytopenia (ITP) in adults. Methods  A retrospective analysis of clinical data was conducted on 205 adult patients with relapsed ITP who received first-line combination therapy or monotherapy in multiple centers across China from January 2010 to December 2022. The study evaluated the patients' clinical characteristics, efficacy, and safety. Results  We found that the proportion of patients with platelet counts in complete response was significantly higher in the combination group (71.83%) compared with the IVIg group (43.48%) and the corticosteroids group (23.08%). The mean PLT _max in the combination group (178 × 10 ⁹ /L) was significantly higher than that in the IVIg group (109 × 10 ⁹ /L) and the corticosteroids group (76 × 10 ⁹ /L). Additionally, the average time for platelet counts to reach 30 × 10 ⁹ /L, 50 × 10 ⁹ /L, and 100 × 10 ⁹ /L in the combination group was significantly shorter than in the monotherapy groups. The proportion curves for reaching these platelet counts during treatment were also significantly different from those in the monotherapy groups. However, there were no significant differences in the effective rate, clinical characteristics, and adverse events among the three groups. Conclusion  We concluded that combining IVIg and corticosteroids was a more effective and faster treatment for relapsed ITP in adults than using either therapy alone. The findings of this study provided clinical evidence and reference for the use of first-line combination therapy in the treatment of relapsed ITP in adults.

Testing strategies used in the diagnosis of rare inherited bleeding disorders

INTRODUCTION

Rare Bleeding Disorders have a low population prevalence and may not be recognized by most clinicians. In addition, knowledge gaps of the indicated laboratory tests and their availability add to the potential for delayed diagnosis or misdiagnosis. The lack of widely available commercial, regulatory body approved esoteric tests limit them to reference laboratories, thus limiting easy access for patients.

AREAS COVERED

A literature search of Pubmed, Medline, Embase and review of international society guidelines was performed. Additional references from published articles were reviewed. A patient-centered approach to recognition and evaluation of RBD is discussed.

EXPERT OPINION

Recognition of RBD relies on obtaining a detailed patient personal and family hemostatic history. Inquiry into a history of involvement of other organ systems is important and if present should lead to suspicion of an inherited platelet disorder or a variant of Ehlers Danlos Syndrome. Multiple factors contribute to the complexity of development of efficient algorithms for diagnostic testing. Limitations in diagnostic sensitivity and specificity of screening tests, diagnostic tests, and esoteric tests further compound the complexity of establishing a diagnosis. Educational efforts focusing on clinician awareness of RBDs and available testing options are vital for optimal management of such patients.

A novel quantitative method to evaluate the contribution of platelet products to white thrombus formation in reconstituted blood under flow conditions

BACKGROUND AND OBJECTIVES

Currently, the quality of platelet (PLT) products is evaluated using a series of in vitro tests, which only analyse PLTs as an inspection material. However, it would be ideal to assess the physiological functions of PLTs under conditions similar to the sequential blood haemostatic process. In this study, we attempted to establish an in vitro system where the thrombogenicity of PLT products was evaluated in the presence of red blood cells (RBCs) and plasma using a microchamber under constant shear stress (600/s).

MATERIALS AND METHODS

Blood samples were reconstituted by mixing PLT products, standard human plasma (SHP) and standard RBCs. Each component was serially diluted keeping the other two components fixed. The samples were applied onto a flow chamber system (Total Thrombus-formation Analysis System [T-TAS]), and white thrombus formation (WTF) was assessed under large arterial shear conditions.

RESULTS

We observed a good correlation between the PLT numbers in the test samples and WTF. The WTF of samples containing ≦10% SHP was significantly lower than those containing ≧40% SHP, and no difference was observed in WTF among samples containing 40%-100% SHP. WTF significantly declined in the absence of RBCs, whereas no change in WTF was observed in the presence of RBCs, over haematocrit range of 12.5%-50%.

CONCLUSION

The WTF assessed on the T-TAS using reconstituted blood may serve as a new physiological blood thrombus test to quantitatively determine the quality of PLT products.

The hemostatic profile of cold-stored whole blood from non-greyhound and greyhound dogs over 42 days

Objectives

To compare the hemostatic characteristics of cold-stored whole blood (CSWB) from non-greyhound dogs (NGD) and greyhound dogs (GD) over 42 days of storage, notably, platelet closure time (PCT) (NGD only), manual platelet count (PLT) (GD only), ellagic acid (INTEM) and tissue factor activated (EXTEM) rotational thromboelastometry, prothrombin (PT) and activated partial thromboplastin time (aPTT), fibrinogen concentration (FIB), and the activities of factors (F) FII, FV, FVII, FVIII, FIX, FX, FXIII antigen (FXIII:Ag), and von Willebrand factor antigen (vWF:Ag).

Design

Whole blood from 10 NGD and 10 GD, was refrigerated in CPD blood bags at 4°C for 42 days. Blood was analyzed before refrigeration (day 0) and at day 1 (d1), 3, 5, 7, 10, 14, 17, 21, 24, 28, 31, 35, 38, and 42. Multivariate linear mixed effects models were created to evaluate coagulation parameters over time and compare NGD and GD. Data are summarized as estimated marginal means with 95% confidence intervals. Significance was set at P < 0.05.

Results

The PCT for all NGD CSWB was above the device limit by d7. The PLT for GD CSWB did not change during storage. The mean alpha-angle for INTEM and EXTEM decreased to <50% of baseline at d38 and d31 for NGD, and d31 and d17 for GD CSWB. The mean maximum clot firmness (MCF) for INTEM and EXTEM reduced to <50% of baseline at d42 and d28 for both GD and NGD. PT and aPTT for NGD and GD increased over time. For NGD CSWB, the mean FVIII and vWF:Ag activities decreased to <50% of baseline at d7 and d28, respectively, and FIB reached 0.982 g/dL by d24. For GD CSWB, FVIII, FXIII:Ag and FV activities decreased to <50% of baseline by d3, d38, and d38, respectively, and FIB was 0.982 g/dL at baseline. Alpha-angle and MCF for both INTEM and EXTEM, and activities for FII, FV, FIX, FXIII:Ag were significantly lower, and vWF:Ag was significantly higher overall in GD CSWB compared with NGD. A significant difference in the pattern of change over time was detected between NGD and GD in EXTEM alpha-angle, INTEM and EXTEM MCF, FII, and FVIII activities.

Conclusions

The in vitro viscoelastic parameters of GD and NGD CSWB declines over 42 days, but numerous hemostatic parameters (INTEM and EXTEM alpha-angle and MCF, activity of FII, FV, FV, FVII, FIX, FX, FXIII:Ag, vWF:Ag, and FIB) remain within 50% of baseline for more than 14 days. CSWB from GD compared to NGD has reduced hemostatic activity overall, but a similar pattern of decline for most parameters over time.

Diagnosing Czech Patients with Inherited Platelet Disorders

A single-center study was conducted on 120 patients with inherited disorders of primary hemostasis followed at our hematological center. These patients presented a variety of bleeding symptoms; however, they had no definitive diagnosis. Establishing a diagnosis has consequences for the investigation of probands in families and for treatment management; therefore, we aimed to improve the diagnosis rate in these patients by implementing advanced diagnostic methods. According to the accepted international guidelines at the time of study, we investigated platelet morphology, platelet function assay, light-transmission aggregometry, and flow cytometry. Using only these methods, we were unable to make a definitive diagnosis for most of our patients. However, next-generation sequencing (NGS), which was applied in 31 patients, allowed us to establish definitive diagnoses in six cases (variants in ANKRD26, ITGA2B, and F8) and helped us to identify suspected variants (NBEAL2, F2, BLOC1S6, AP3D1, GP1BB, ANO6, CD36, and ITGB3) and new suspected variants (GFI1B, FGA, GP1BA, and ITGA2B) in 11 patients. The role of NGS in patients with suspicious bleeding symptoms is growing and it changes the diagnostic algorithm. The greatest disadvantage of NGS, aside from the cost, is the occurrence of gene variants of uncertain significance.

The use of a low-flux hemo-dialyzer is associated with impaired platelet aggregation in patients undergoing chronic hemodialysis

In patients with chronic hemodialysis (HD), both abnormal thrombotic and bleeding events are commonly observed. Uremic platelet dysfunction is one of the important attributing factors. Moreover, HD may also result in aggregation dysfunction of platelets during the therapeutic procedure. However, how the HD process affects platelet and coagulation function is unknown and dialyzer membrane flux could have an impact on it. We aimed to compare the impacts of low-flux and high-flux HD on the platelet function of patients undergoing chronic HD. This was a cross-sectional study conducted in the HD unit of E-Da hospital in Taiwan. A total of 78 patients with maintenance HD three times per week for more than one year, including 40 with high- and 38 with low-flux hemodialysis, were recruited. Their platelet functions were evaluated using an in vitro platelet function analyzer (PFA-100) before and after the HD session. Of the 78 patients undergoing HD, 60 (76%) had prolonged pre-dialysis collagen/epinephrine (CEPI) and collagen/adenosine diphosphate closure times. Those receiving low-flux dialyzer had a significant increase in CEPI closure time (pre-dialysis 212.3 ± 62.1 seconds. post-dialysis 241.5 ± 64.3 seconds, P = .01), but not collagen/adenosine diphosphate closure time, after HD. After adjusting confounding factors, only the low-flux dialyzer demonstrated an independent association with the prolonged CEPI closure time after HD therapy (odds ratio = 23.31, 95% CI: 1.94-280.61, P = .01). We observed that impaired platelet aggregation is prevalent in patients undergoing chronic HD. Therefore, the use of low-flux dialyzers may further worsen platelet aggregation after dialysis. Patients with uremic bleeding diathesis should take precautions. We suggest that further studies using flow cytometry should be conducted to explore the mechanism of dialysis flux and platelet activity during HD.

The Pharmacological Effects of Silver Nanoparticles Functionalized with Eptifibatide on Platelets and Endothelial Cells

Purpose

In the search for new drug delivery platforms for cardiovascular diseases and coating of medical devices, we synthesized eptifibatide-functionalized silver nanoparticles (AgNPs-EPI) and examined the pharmacological activity of AgNPs-EPI on platelets and endothelial cells in vitro and ex vivo.

Methods

Spherical AgNPs linked to eptifibatide were synthesized and characterized. Cytotoxicity was measured in microvascular endothelial cells (HMEC-1), platelets and red blood cells. Platelet mitochondrial respiration was measured using the Oxygraph-2k, a high-resolution modular respirometry system. The effect of AgNPs-EPI on the aggregation of washed platelets was measured by light aggregometry and the ex vivo occlusion time was determined using a reference laboratory method. The surface amount of platelet receptors such as P-selectin and GPIIb/IIIa was measured. The influence of AgNPS-EPI on blood coagulation science was assessed. Finally, the effect of AgNPs-EPI on endothelial cells was measured by the levels of 6-keto-PGF1alpha, tPa, cGMP and vWF.

Results

We describe the synthesis of AgNPs using eptifibatide as the stabilizing ligand. The molecules of this drug are directly bonded to the surface of the nanoparticles. The synthesized AgNPs-EPI did not affect the viability of platelets, endothelial cells and erythrocytes. Preincubation of platelets with AgNPs-EPI protected by mitochondrial oxidative phosphorylation capacity. AgNPs-EPI inhibited aggregation-induced P-selectin expression and GPIIb/IIIa conformational changes in platelets. AgNPs-EPI caused prolongation of the occlusion time in the presence of collagen/ADP and collagen/adrenaline. AgNPs-EPI regulated levels of 6-keto-PGF1alpha, tPa, vWf and cGMP produced in thrombin stimulated HMEC-1 cells.

Conclusion

AgNPs-EPI show anti-aggregatory activity at concentrations lower than those required by the free drug acting via regulation of platelet aggregation, blood coagulation, and endothelial cell activity. Our results provide proof-of-principle evidence that AgNPs may be used as an effective delivery platform for antiplatelet drugs.

Platelet abnormalities in patients with Parkinson's disease undergoing preoperative evaluation for deep brain stimulation

Normal hemostatic function is important for reduction of the risk of intracranial hemorrhage during stereotactic neurosurgery including deep brain stimulation (DBS) surgery. This study investigates the hemostatic function in patients with Parkinson’s disease (PD) undergoing preoperative evaluation for DBS, with emphasis on the number and function of platelets. In 107 PD patients, only one had abnormal activated partial prothrombin time and normal prothrombin time. Among the other 106 patients, six (5.7%) had only thrombocytopenia, seven (6.6%) only prolonged bleeding time (BT), and 14 (13.2%) only prolonged closure time (CT) of platelet function analyzer 100 (PFA-100). Totally, 34 of the 106 patients (32.1%) had at least one of three kinds of platelet abnormalities. No factor was found to be associated with the occurrence of platelet abnormalities except that abnormal platelet group and prolonged BT subgroup had more patients using selegiline and lower UPDRS-III motor subscore with medication off than normal platelet group (p < 0.05). The use of selegiline was significantly correlated with prolonged BT (p = 0.0041) and platelet abnormality (p = 0.0197). Therefore, it is important to have detailed evaluation of the hemostatic function for PD patients undergoing preoperative evaluation for DBS, especially the platelet number and function.

Towards 50 years of platelet function analyser (PFA) testing

The platelet function analyser (PFA) is a prevalent platelet function screening instrument, and comes in two models-the original PFA-100 and the contemporary PFA-200. The instruments have 'identical' output, being a 'closure time' (CT). Moreover, normal reference ranges provided by the manufacturer, for the specific test cartridges, are the same for both models. There are three different types of test cartridge: collagen/epinephrine (C/Epi), collagen/adenosine diphosphate (C/ADP), and "Innovance PFA P2Y" (only available in certain geographical locations). The PFA-100 was released in the mid 1990s, and so is approaching 50 years of age. The PFA-200, released in some locations in the mid 2010s, is destined to eventually replace the PFA-100, but is not yet available in the USA. The test system is highly sensitive to von Willebrand disease (VWD; C/Epi and C/ADP) and to aspirin therapy (C/Epi only), but only has moderate sensitivity to defects in platelet function and/or deficiencies in platelet number. Accordingly, recommendations for use for screening platelet function vary according to user experience. Some workers have alternatively used the PFA to assess thrombosis risk or pre-operative bleeding risk. In this review, we provide an overview of the history of PFA, and summarise its current clinical utility.

Assay validity of point-of-care platelet function tests in thrombocytopenic blood samples

Introduction

Point-of-care (POC) platelet function tests are faster and easier to perform than in-depth assessment by flow cytometry. At low platelet counts, however, POC tests are prone to assess platelet function incorrectly. Lower limits of platelet count required to obtain valid test results were defined and a testing method to facilitate comparability between different tests was established.

Materials and methods

We assessed platelet function in whole blood samples of healthy volunteers at decreasing platelet counts (> 100, 80-100, 50-80, 30-50 and < 30 x10⁹/L) using two POC tests: impedance aggregometry and in-vitro bleeding time. Flow cytometry served as the gold standard. The number of platelets needed to reach 50% of the maximum function (ED₅₀) and the lower reference limit (ED_ref) were calculated to define limits of test validity.

Results

The minimal platelet count required for reliable test results was 100 x10⁹/L for impedance aggregometry and in-vitro bleeding time but only 30 x10⁹/L for flow cytometry. Comparison of ED₅₀ and ED_ref showed significantly lower values for flow cytometry than either POC test (P value < 0.05) but no difference between POC tests nor between the used platelet agonists within a test method.

Conclusion

Calculating the ED₅₀ and ED_ref provides an effective way to compare values from different platelet function assays. Flow cytometry enables correct platelet function testing as long as platelet count is > 30 x10⁹/L whereas impedance aggregometry and in-vitro bleeding time are inconsistent unless platelet count is > 100 x10⁹/L.

Advances in the diagnosis of heritable platelet disorders

The last decade has seen large increases in the number of patients registered with heritable platelet disorders in national databases of bleeding disorders. Although individually rare, collectively they are a relatively common cause of heritable bleeding. This revolution has come about through the application of high-throughput sequencing strategies and efforts to standardize diagnostic testing. There is renewed interest in established parameters such as platelet volume and utilising simple tools such as blood smears. The diagnostic yield from peripheral blood smears can be improved with new microscopy techniques that could potentially assist in determining which patients need to be referred to tertiary centres for specialist testing. A better understanding of the other clinical features that can accompany abnormalities of platelet number or function, can lead to better clinical management and prevention of serious complications. There are challenges for clinicians who need to be aware of these developments, understand the limitations of new diagnostic techniques and keep abreast of strategies for incorporation into clinical practice. This review discusses some of these approaches, the limitations that clinicians need to be aware of and techniques that may enter clinical use in the future.

Platelet function testing: Current practice among clinical centres in Northern Europe

Introduction

Platelet function tests are used to screen and diagnose patients with possible inherited platelet function defects (IPFD). Some acquired platelet dysfunction may be caused by certain drugs or comorbidities, which need to be excluded before testing.

Aims

To identify current practice among centres performing platelet function tests in Northern Europe.

Methods

A total of 14 clinical centres from Sweden (six), Finland (two), Denmark (two), Norway (one), Estonia (two) and Iceland (one) completed the survey questionnaire, the population capture area of about 29.5 million.

Results

Six of the 14 (42.8%) centres providing platelet function assessment represent comprehensive treatment centres (EUHANET status). A Bleeding score (BS) or ISTH bleeding assessment tool (ISTH BAT score) is evaluated in 11/14 (78.6%) centres and family history in all. Five/14 centres (35.7%) use structured preanalytical patient instructions, and 10/14 (71.4%) recorded questionnaire on the preassessment of avoidance of any drugs or natural products affecting platelet functions. Preliminary investigations of screening tests of coagulation are performed in 10/14 (71.4%), while in 4/14 (28.6%), the diagnostic work‐up of IPFD and von Willebrand disease (VWD) is performed simultaneously. The work‐up of IPFD includes peripheral blood smear in 10/14 (71.4%), platelet aggregometry in all, flow cytometry in 10/14 (71.4%) and Platelet Function Analysis (PFA) in 3/11 (28.6%). Molecular genetic diagnosis is available in 7/14 (50%) centres.

Conclusions

The considerable variability in the current practice illustrates the need for harmonization between the Northern European centres according to the international registers (i.e. EUHASS) and IPFD guidelines (ISTH, EHA).

Diagnostic workup of inherited platelet disorders

Inherited platelet disorders (IPDs) can cause mucocutaneous bleeding due to impaired primary hemostatic function of platelets, thrombocytopenia, or both. Recent advances in molecular technology can help identify many genes related to platelet biology, control the overall steps of megakaryopoiesis, and cause IPD. In this article, currently available laboratory tools for diagnosing IPDs with the characteristic laboratory features of each IPD are reviewed, and a general diagnostic approach for the evaluation of IPD patients is presented.

Screening and diagnosis of inherited platelet disorders

Inherited platelet disorders are important conditions that often manifest with bleeding. These disorders have heterogeneous underlying pathologies. Some are syndromic disorders with non-blood phenotypic features, and others are associated with an increased predisposition to developing myelodysplasia and leukemia. Platelet disorders can present with thrombocytopenia, defects in platelet function, or both. As the underlying pathogenesis of inherited thrombocytopenias and platelet function disorders are quite diverse, their evaluation requires a thorough clinical assessment and specialized diagnostic tests, that often challenge diagnostic laboratories. At present, many of the commonly encountered, non-syndromic platelet disorders do not have a defined molecular cause. Nonetheless, significant progress has been made over the past few decades to improve the diagnostic evaluation of inherited platelet disorders, from the assessment of the bleeding history to improved standardization of light transmission aggregometry, which remains a "gold standard" test of platelet function. Some platelet disorder test findings are highly predictive of a bleeding disorder and some show association to symptoms of prolonged bleeding, surgical bleeding, and wound healing problems. Multiple assays can be required to diagnose common and rare platelet disorders, each requiring control of preanalytical, analytical, and post-analytical variables. The laboratory investigations of platelet disorders include evaluations of platelet counts, size, and morphology by light microscopy; assessments for aggregation defects; tests for dense granule deficiency; analyses of granule constituents and their release; platelet protein analysis by immunofluorescent staining or flow cytometry; tests of platelet procoagulant function; evaluations of platelet ultrastructure; high-throughput sequencing and other molecular diagnostic tests. The focus of this article is to review current methods for the diagnostic assessment of platelet function, with a focus on contemporary, best diagnostic laboratory practices, and relationships between clinical and laboratory findings.

Multiparameter platelet function analysis of bleeding patients with a prolonged platelet function analyser closure time

Patients referred for evaluation of bleeding symptoms occasionally have a prolonged platelet function analyser (PFA) closure time, without evidence for von Willebrand disease or impaired platelet aggregation. The aim of this study was to establish a shear‐dependent platelet function defect in these patients. Patients were included based on high bleeding score and prior PFA prolongation. Common tests of von Willebrand factor (VWF) and platelet function and exome sequencing were performed. Microfluidic analysis of shear‐dependent collagen‐induced whole‐blood thrombus formation was performed. In 14 PFA‐only patients, compared to healthy volunteers, microfluidic tests showed significantly lower platelet adhesion and thrombus formation parameters. This was accompanied by lower integrin activation, phosphatidylserine exposure and P‐selectin expression. Principal components analysis indicated VWF as primary explaining variable of PFA prolongation, whereas conventional platelet aggregation primarily explained the reduced thrombus parameters under shear. In five patients with severe microfluidic abnormalities, conventional platelet aggregation was in the lowest range of normal. No causal variants in Mendelian genes known to cause bleeding or platelet disorders were identified. Multiparameter assessment of whole‐blood thrombus formation under shear indicates single or combined effects of low–normal VWF and low–normal platelet aggregation in these patients, suggesting a shear‐dependent platelet function defect, not detected by static conventional haemostatic tests.

Platelet Distribution Width Is Associated with P-Selectin Dependent Platelet Function: Results from the Moli-Family Cohort Study

Defined as an index of platelet size heterogeneity, the platelet distribution width (PDW) is still a poorly characterized marker of platelet function in (sub)clinical disease. We presently validated PDW as a marker of P-selectin dependent platelet activation in the Moli-family cohort. Platelet-bound P-selectin and platelet/leukocyte mixed aggregates were measured by flow cytometry in freshly collected venous blood, both before and after in vitro platelet activation, and coagulation time was assessed in unstimulated and LPS- or TNFα-stimulated whole blood. Closure Times (CT) were measured in a Platelet Function Analyzer (PFA)-100. Multivariable linear mixed effect regression models (with age, sex and platelet count as fixed and family structure as random effect) revealed PDW to be negatively associated with platelet P-selectin, platelet/leukocyte aggregates and von Willebrand factor (VWF), and positively with PFA-100 CT, and LPS- and TNF-α-stimulated coagulation times. With the exception of VWF, all relationships were sex-independent. In contrast, no association was found between mean platelet volume (MPV) and these variables. PDW seems a simple, useful marker of ex vivo and in vitro P-selectin dependent platelet activation. Investigations of larger cohorts will define the usefulness of PDW as a risk predictor of thrombo-inflammatory conditions where activated platelets play a contributing role.

Diagnostic approach to the patient with a suspected inherited platelet disorder: Who and how to test

Bleeding and thrombocytopenia are common referrals to the pediatric and adult hematology practice. The differential diagnosis encompasses a wide spectrum of entities that vary in acuity, severity, and etiology. Most will be acquired (especially in adult patients), but many can be inherited, and some may have manifestations affecting other organ systems. The first step: defining whether the symptoms and/or laboratory findings are clinically significant and warrant additional work-up, can be equally as challenging as reaching the diagnosis itself. How much bleeding is too much to be considered normal? How low of a platelet count is too low? Once the decision has been made to pursue additional studies, considering the increasing number of laboratory tests available, the diagnostic process can be complex. In this article, we outline a general approach for the evaluation of patients in whom an inherited platelet disorder is being considered. We present two clinical vignettes as introduction to the diagnostic approach to inherited platelet disorders. We describe the rationale for the different types of tests that are clinically available, their limitations, and finally the challenges that are frequently encountered in the interpretation of results. We also intend to provide some guidance on the expected phenotype in terms of severity of bleeding and/or thrombocytopenia according to the etiology of the inherited disorder. Our goal is to provide the practicing hematologist with a practical framework that is clinically applicable in their daily practice.

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.

Inherited Platelet Disorders: An Updated Overview

Platelets play a major role in hemostasis as ppwell as in many other physiological and pathological processes. Accordingly, production of about 10¹¹ platelet per day as well as appropriate survival and functions are life essential events. Inherited platelet disorders (IPDs), affecting either platelet count or platelet functions, comprise a heterogenous group of about sixty rare diseases caused by molecular anomalies in many culprit genes. Their clinical relevance is highly variable according to the specific disease and even within the same type, ranging from almost negligible to life-threatening. Mucocutaneous bleeding diathesis (epistaxis, gum bleeding, purpura, menorrhagia), but also multisystemic disorders and/or malignancy comprise the clinical spectrum of IPDs. The early and accurate diagnosis of IPDs and a close patient medical follow-up is of great importance. A genotype-phenotype relationship in many IPDs makes a molecular diagnosis especially relevant to proper clinical management. Genetic diagnosis of IPDs has been greatly facilitated by the introduction of high throughput sequencing (HTS) techniques into mainstream investigation practice in these diseases. However, there are still unsolved ethical concerns on general genetic investigations. Patients should be informed and comprehend the potential implications of their genetic analysis. Unlike the progress in diagnosis, there have been no major advances in the clinical management of IPDs. Educational and preventive measures, few hemostatic drugs, platelet transfusions, thrombopoietin receptor agonists, and in life-threatening IPDs, allogeneic hematopoietic stem cell transplantation are therapeutic possibilities. Gene therapy may be a future option. Regular follow-up by a specialized hematology service with multidisciplinary support especially for syndromic IPDs is mandatory.

Multiparameter microfluidics assay of thrombus formation reveals increased sensitivity to contraction and antiplatelet agents at physiological temperature

INTRODUCTION

Current developments to assess qualitative and quantitative platelet traits in flowed whole-blood are based on microfluidic devices that mostly operate at room temperature. However, operation at physiological temperature (37 °C) may increase the assay's sensitivity, and facilitates the comparison to other platelet function tests of the diagnostic laboratory.

MATERIALS AND METHODS

We adapted the conventional microspot-based microfluidic device with a simple thermo-coupled pre-heating module. Automated analysis of microscopic images assisted in obtaining five time-dependent parameters of thrombus formation over collagen microspots (shear rate 1000 s^-1). These modifications allowed rapid testing of control and patient blood samples at physiological temperature.

RESULTS AND CONCLUSION

The higher temperature enhanced platelet adhesion and aggregation as well as late thrombus characteristics such as size and contraction, when compared to room temperature. Moreover, assessment at 37 °C indicated a time-dependent impairment of the thrombus parameters in blood from patients taking common antiplatelet medication, i.e. aspirin and/or clopidogrel. This pointed to increased contribution of the autocrine platelet agonists thromboxane A₂ and ADP in the buildup of contracted thrombi under flow. Overall, this study underlined the advantage of multiparameter assessment of microfluidic thrombus formation in detecting an acquired platelet dysfunction, when operating at physiological temperature. This work may bring microfluidics tests closer to the diagnostic laboratory.

Establishment of reference intervals for Platelet Function Analyzer -100 closure time in Algerian adults

INTRODUCTION

The Platelet Function Analyzer-100 (PFA-100) is a point of care instrument that simulates plug formation under high shear flow. The PFA-100 measures the time required to occlude the aperture in a biochemically active cartridge and is expressed in a term of closure time (CT). In Algeria, the reference values used in clinical laboratories are of Western origin. However, ethnic, genetic, dietary environmental, and diet differences between populations may affect reference intervals. We established the reference intervals of PFA-100 closure times in healthy Algerian adults according to the International Federation of Clinical Chemistry method, and we compared them with those of Western and Asian countries.

MATERIAL AND METHODS

We enrolled 303 healthy blood donors in the study. 218 subjects met inclusion criteria. We analyzed the blood sample on the PFA-100 for CT with both the collagen epinephrine and collagen ADP cartridges.

RESULTS

The reference intervals of PFA-100 collagen epinephrine CT and PFA-100 collagen ADP CT were 91-207 seconds and 71-144 seconds, respectively. Compared to Western and Asian populations, there were significant differences. The upper limits of CTs were higher for Algerians in this study. Our findings show that many healthy Algerians would be incorrectly identified as having a primary hemostasis abnormality according to the reference intervals of the manufacturer and scientific literature.

CONCLUSION

This report provides the first reference intervals for PFA-100 CTs in healthy Algerian adults. These results improve the accuracy of diagnosis and patient care in Algeria.

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.

Platelet function and microvesicle generation in patients with hemophilia A

Our results do not support any effect of FVIII on platelet function in patients with severe HA treated under the regime of prophylaxis.

Correlation between PlateletWorks® and PFA-100® for Measuring Platelet Function before Urgent Surgery in Patients with Chronic Antiplatelet Therapy

Hemostasis is crucial for reducing bleeding during surgical procedures. The points-of-care based on the platelet function test could be useful to minimize the complications related to chronic antiplatelet therapy during surgery. The present study is aimed at comparing two point-of-care platelet function devices-Platelet Function Analyzer PFA-100^® (Siemens Canada, Mississauga, ON, Canada) and Plateletworks^®(Helena Laboratories, Beaumont, TX, USA). Our objective is to evaluate if they provide comparable and useful information to manage anti-aggregate patients before surgery. We included patients with a femoral fracture receiving chronic antiplatelet therapy and a median age of 89 years (range from 70 to 98). A platelet function evaluation was performed on all patients before surgery using both devices-Plateletworks^® and PFA-100^®. The correlation between Plateletworks^® and PFA-100^® was performed using Cohen's Kappa coefficient. Twenty consecutive patients participated in the trial; 16 patients were under treatment with 75 mg/day of clopidogrel, three with >300 mg/day of acetylsalicylic acid (ASA), and only one was in treatment with both antiplatelet agents. Cohen's Kappa coefficient was 0.327 comparing PFA-100^®-ADP (adenosine diphosphate) and Plateletworks^® and, 0.200 comparing PFA-100^®-EPI (epinephrine) and Plateletworks^®. In conclusion, we found a weak concordance comparing PFA-100^® and Plateletworks^®. This could partially be due to the advanced age of the included patients. However, given the limited sample size, more studies are necessary to confirm these results.

Scalable manufacture of a disposable, storage-stable eight-channel microfluidic device for rapid testing of platelet, coagulation, and drug function under whole blood flow

Custom polydimethylsiloxane (PDMS) microfluidic devices allow for small-volume human blood research under hemodynamic conditions of bleeding and clotting. However, issues of PDMS molding/assembly, bio-coating, and sample preparation often limit their point-of-care use. We aim to develop a microfluidic device that has the same utility as previously established PDMS devices but which is more usable in point-of-care operation. We designed an injection-molded 1 × 3 in.² device with eight flow paths crossing a bio-printed surface of a collagen/tissue factor. The device is rapidly primed and compatible with multi-channel pipetting (<0.5 ml blood) and operates under venous or arterial shear rates using constant flow rate or constant pressure modes. Platelet and fibrin deposition were monitored dynamically by the imaging of immunofluorescence. For whole blood clotting at a wall shear rate of 200 s^-1, the intrachip CV at 400 s for platelet and fibrin deposition was 10% and the interdonor CV at 400 s was 30% for platelet and 22% for fibrin deposition (across 10 healthy donors). No significant difference was detected for samples tested on a new chip vs a chip stored for 6 months at 4 °C. Using the fibrin signal, dose-response testing of whole blood revealed IC₅₀'s of 120 nM for rivaroxaban and apixaban, and 60 nM for dabigatran. A complete reversal of apixaban inhibition was observed for an equimolar addition of Xa DOAC reversal agent Andexanet Alfa. We demonstrate the ability to manufacture single-use, storage-stable eight-channel chips. In clinical settings, such chips may help evaluate patient bleeding risk, therapy choice, drug activity, or reversal.

The role of platelet function analyzer-200 in predicting perioperative bleeding risk

BACKGROUND/AIMS

Various preoperative screening tests, such as platelet count, prothrombin time, activated partial thromboplastin time, and bleeding time, have been widely used to evaluate the risk of bleeding during surgery. Use of platelet function analyzer (PFA)-100/200 for assessing platelet function instead of bleeding time is increasing. However, its role in predicting the perioperative risk of bleeding remains controversial.

METHODS

Data of 703 patients who underwent surgery under general anesthesia were retrospectively analyzed. Preoperative platelet function was measured using PFA-200 system and the association with intraoperative bleeding was assessed. Additionally, other variables that could affect PFA-200 results were assessed by logistic regression analysis.

RESULTS

Collagen/epinephrine (COL/EPI) test was prolonged in 199/703 (28.3%) patients (EPI group), while 99/212 (46.7%) patients showed COL/adenosine diphosphate test abnormalities. Bleeding over 300 mL during surgery occurred in 14.3% and 20.1% of patients in the normal and EPI groups, respectively (p = 0.058). In addition, red blood cell transfusion within 72 hours after surgery rate was significantly higher in the EPI group than in the normal group (31.7% vs. 23.4%, p = 0.024). In multivariate logistic analysis, prolongation closure time with COL/EPI (p = 0.068) was marginally associated with risk of bleeding during surgery. Furthermore, PFA-200 results were influenced by various factors, such as nonsteroidal anti-inflammatory drug use, blood group, hematocrit, and time of blood collection.

CONCLUSION

Preoperative PFA-200 test may be helpful in predicting the risk of perioperative bleeding. However, its results should be carefully interpreted because they are affected by several factors.

Comparison of acetylsalicylic acid and clopidogrel non-responsiveness assessed by light transmittance aggregometry and PFA-100® in patients undergoing neuroendovascular procedures

Objectives

Dual platelet inhibition is commonly used for prevention of cardiovascular events in patients undergoing neuroendovascular procedures. Non-responsiveness to platelet inhibitors may be associated with adverse outcomes. The aim of this study was to evaluate the reliability of the platelet function analyzer PFA-100® in comparison to light transmittance aggregometry (LTA) for monitoring clopidogrel and acetylsalicylic acid (ASA) non-responsiveness in a cohort of patients treated for intracranial aneurysm or cranial artery stenosis.

Methods

Non-responsiveness to clopidogrel and ASA was assessed by LTA using adenosine diphosphate (ADP) and arachidonic acid and by PFA-100® with the ADP/prostaglandin E1 (PGE1) and collagen/epinephrine cartridges, respectively.

Results

A total of 203 patients (145 females; median age, 57 years) were analyzed. Agreement between the two tests was poor for clopidogrel non-responsiveness (ƙ=0.19) and not better than chance for ASA non-responsiveness (ƙ=0.01). Clopidogrel non-responsiveness by LTA and PFA-100® was associated with higher von Willebrand factor antigen and activity levels. ADP-induced platelet disaggregation was lower in patients with clopidogrel non-responsiveness as assessed by PFA-100®. Clopidogrel non-responsiveness by LTA was associated with a higher prevalence of diabetes and a higher body mass index (BMI). Adverse outcomes (death, thromboembolism, or in-stent thrombosis) occurred in 13% (n=26) of all patients independently of ASA and clopidogrel non-responsiveness as assessed by both devices.

Conclusions

Our results show that LTA and PFA-100® are not interchangeable in the assessment of ASA and clopidogrel non-responsiveness in patients undergoing neuroendovascular interventions.

Advances in Platelet Function Testing-Light Transmission Aggregometry and Beyond

Platelet function testing is essential for the diagnosis of hemostasis disorders. While there are many methods used to test platelet function for research purposes, standardization is often lacking, limiting their use in clinical practice. Light transmission aggregometry has been the gold standard for over 60 years, with inherent challenges of working with live dynamic cells in specialized laboratories with independent protocols. In recent years, standardization efforts have brought forward fully automated systems that could lead to more widespread use. Additionally, new technical approaches appear promising for the future of specialized hematology laboratories. This review presents developments in platelet function testing for clinical applications.

Cranberry supplementation as a cause of major intraoperative bleeding during vascular surgery due to aspirin-like platelet inhibition

We report severe excessive bleeding at initiation of vascular surgery in a 74-year-old woman with thoracoabdominal aortic aneurysm undergoing thoracic endovascular aortic repair. After extensive workup, bleeding cause was determined to be an aspirin-like effect from supplemental cranberry intake. After asking the patient to stop cranberry consumption, the aspirin-like effect ceased, and the patient underwent successful thoracic endovascular aortic repair. Cranberry consumption may create an aspirin-like effect that increases risk of bleeding. Providers should be aware of potential adverse effects of cranberries on platelet function and consider inquiring about supplement use in the perioperative period.

Platelet Function: Meloxicam Intravenous in Whole Blood Samples From Healthy Volunteers

Nonsteroidal anti‐inflammatory drugs (NSAIDs) are effective treatments for pain but may induce bleeding events due to platelet dysfunction associated with inhibition of cyclooxygenase (COX)‐1 impairing thromboxane production. An intravenous nanocrystal formulation of meloxicam, a COX‐2 preferential nonsteroidal anti‐inflammatory drug, is under development for the treatment of moderate to severe pain. This single‐center ex vivo study evaluated the effect of meloxicam intravenous and ketorolac on platelet function in whole blood samples from healthy volunteers. Each whole blood sample was aliquoted to allow analysis using a platelet function analyzer under negative control (untreated), positive control (2 therapeutic ketorolac concentrations), and meloxicam intravenous (1 therapeutic, 3 supratherapeutic concentrations) using both collagen with epinephrine and collagen with adenosine diphosphate reagent cartridges. The platelet function analyzer determines closure time by simulating platelet adhesion and aggregation following vascular injury. The final analysis set included data from 8 subjects. The collagen with adenosine diphosphate analysis (sensitive to thrombocytopathies) showed no significant differences in closure time for meloxicam‐ or ketorolac‐treated samples and untreated control. The collagen with epinephrine analysis (sensitive to aspirin‐induced platelet abnormalities) produced no significant difference in closure time between any meloxicam concentration and untreated control. Ketorolac was associated with significantly longer closure times vs untreated control at both the 2.5‐ and 5‐µg/mL concentrations (P = .003 and .0257, respectively) and vs meloxicam at several concentrations. Similar results were observed when all analyzed samples were included. Meloxicam intravenous had no significant effect on closure times at therapeutic or supratherapeutic concentrations in this ex vivo study.

Disease progression and defects in primary hemostasis as major cause of bleeding in multiple myeloma

BACKGROUND AND OBJECTIVES

In patients with multiple myeloma (MM), unexpected bleeding complications remain a major issue. Since routine coagulation parameters are often inconspicuous, diagnosis and treatment of the underlying coagulation disorders are challenging.

PATIENTS AND METHODS

In our single-center observational study, we analyzed 164 patients with MM for coagulation disorders and bleeding complications.

RESULTS

Prolonged closure times (CTs), measured by PFA-100, were the most common, abnormal coagulation test, found in 66% of bleeding patients vs 5% in non-bleeding, followed by qualitative defects of von Willebrand factor (VWF:CB/VWF:Ag ratios), found in 34% vs 1% in the non-bleeding group. Increased serum free light chains (SFLC) and SFLC ratios were significantly associated with prolonged CTs and acquired von Willebrand syndrome (AVWS). Prolonged CTs and AVWS were associated with disease progression, determined by dynamics of SFLC ratios (P < .001), serum creatinine level (P = .013), Beta-2 microglobulin (P = .03), LDH (P = .016), and bone marrow infiltration (P < .001). Of note, response to myeloma therapy was frequently correlated with normalization of coagulation parameters.

CONCLUSIONS

Bleeding complications in MM are predominantly caused by defects in primary hemostasis and associated with disease progression. In a peri-interventional workup, determination of CTs and VWF:CB/VWF:Ag ratios are of significant importance to assess bleeding risk.

Whole Blood Based Multiparameter Assessment of Thrombus Formation in Standard Microfluidic Devices to Proxy In Vivo Haemostasis and Thrombosis

Microfluidic assays are versatile tests which, using only small amounts of blood, enable high throughput analyses of platelet function in several minutes. In combination with fluorescence microscopy, these flow tests allow real-time visualisation of platelet activation with the possibility of examining combinatorial effects of wall shear rate, coagulation and modulation by endothelial cells. In particular, the ability to use blood and blood cells from healthy subjects or patients makes this technology promising, both for research and (pre)clinical diagnostic purposes. In the present review, we describe how microfluidic devices are used to assess the roles of platelets in thrombosis and haemostasis. We place emphasis on technical aspects and on experimental designs that make the concept of "blood-vessel-component-on-a-chip" an attractive, rapidly developing technology for the study of the complex biological processes of blood coagulability in the presence of flow.

Fundamentals for a Systematic Approach to Mild and Moderate Inherited Bleeding Disorders: An EHA Consensus Report

Healthy subjects frequently report minor bleedings that are frequently ‘background noise’ of normality rather than a true disorder. Nevertheless, unexpected or unusual bleeding may be alarming. Thus, the distinction between normal and pathologic bleeding is critical. Understanding the underlying pathologic mechanism in patients with an excessive bleeding is essential for their counseling and treatment. Most of these patients with significant bleeding will result affected by non-severe inherited bleeding disorders (BD), collectively denominated mild or moderate BD for their relatively benign course. Unfortunately, practical recommendations for the management of these disorders are still lacking due to the current state of fragmented knowledge of pathophysiology and lack of a systematic diagnostic approach. To address this gap, an International Working Group (IWG) was established by the European Hematology Association (EHA) to develop consensus-based guidelines on these disorders. The IWG agreed that grouping these disorders by their clinical phenotype under the single category of mild-to-moderate bleeding disorders (MBD) reflects current clinical practice and will facilitate a systematic diagnostic approach. Based on standardized and harmonized definitions a conceptual unified framework is proposed to distinguish normal subjects from affected patients. The IWG proposes a provisional comprehensive patient-centered initial diagnostic approach that will result in classification of MBD into distinct clinical-pathological entities under the overarching principle of clinical utility for the individual patient. While we will present here a general overview of the global management of patients with MBD, this conceptual framework will be adopted and validated in the evidence-based, disease-specific guidelines under development by the IWG.

Influence of ABO Locus on PFA-100 Collagen-ADP Closure Time Is Not Totally Dependent on the Von Willebrand Factor. Results of a GWAS on GAIT-2 Project Phenotypes

(1) Background: In a previous study, we found that two phenotypes related to platelet reactivity, measured with the PFA-100 system, were highly heritable. The aim of the present study was to identify genetic determinants that influence the variability of these phenotypes: closure time of collagen-ADP (Col-ADP) and of collagen-epinephrine (Col-Epi). (2) Methods: As part of the GAIT-2 (Genetic Analysis of Idiopathic Thrombophilia (2) Project, 935 individuals from 35 large Spanish families were studied. A genome-wide association study (GWAS) with ≈ 10 M single nucleotide polymorphisms (SNPs) was carried out with Col-ADP and Col-Epi phenotypes. (3) Results: The study yielded significant genetic signals that mapped to the ABO locus. After adjusting both phenotypes for the ABO genotype, these signals disappeared. After adjusting for von Willebrand factor (VWF) or for coagulation factor VIII (FVIII), the significant signals disappeared totally for Col-Epi phenotype but only partially for Col-ADP phenotype. (4) Conclusion: Our results suggest that the ABO locus exerts the main genetic influence on PFA-100 phenotypes. However, while the effect of the ABO locus on Col-Epi phenotype is mediated through VWF and/or FVIII, the effect of the ABO locus on Col-ADP phenotype is partly produced through VWF and/or FVIII, and partly through other mechanisms.

Update on diagnostic testing for platelet function disorders: What is practical and useful?

INTRODUCTION

Platelet function disorders (PFD) are an important group of bleeding disorders that require validated and practical laboratory strategies for diagnosis.

METHODS

This review summarizes the authors' experiences, current literature, and an international survey to evaluate the practices of diagnostic laboratories that offer tests for PFD.

RESULTS

Blood counts, blood film review, and aggregation tests are the most commonly performed investigations for PFD and help determine whether there is thrombocytopenia and/or defective platelet function due to a variety of causes. The performance characteristics of tests for PFD, and the level of evidence that these tests detect bleeding problems, are important issues to determine where tests are useful for diagnostic or correlative purposes, or research only uses. Platelet aggregation assays, and quantitative analysis of platelet dense granule numbers, are tests with good performance characteristics that detect abnormalities associated with increased bleeding in a significant proportion of individuals referred for PFD investigations. Lumiaggregometry estimates of platelet adenosine triphosphate release show greater variability which limits the diagnostic usefulness. Diagnostic laboratories report that fiscal and other constraints, including a lack of high-quality evidence, limit their ability to offer an expanded test menu for PFD.

CONCLUSION

PFD are clinically important bleeding disorders that remain challenging for diagnostic laboratories to investigate. While some PFD tests are well validated for diagnostic purposes, gaps in scientific evidence and resource limitations influence diagnostic laboratory decisions on which PFD tests to offer.

Shear-induced platelet adherence and activation in an in-vitro dynamic multiwell-plate system

Circulating blood cells are prone to varying flow conditions when contacting cardiovascular devices. For a profound understanding of the complex interplay between the blood components/cells and cardiovascular implant surfaces, testing under varying shear conditions is required. Here, we study the influence of arterial and venous shear conditions on the in vitro evaluation of the thrombogenicity of polymer-based implant materials.Medical grade poly(dimethyl siloxane) (PDMS), polyethylene terephthalate (PET) and polytetrafluoroethylene (PTFE) films were included as reference materials. The polymers were exposed to whole blood from healthy humans. Blood was agitated orbitally at low (venous shear stress: 2.8 dyne · cm-2) and high (arterial shear stress: 22.2 dyne · cm-2) agitation speeds in a well-plate based test system. Numbers of non-adherent platelets, platelet activation (P-Selectin positive platelets), platelet function (PFA100 closure times) and platelet adhesion (laser scanning microscopy (LSM)) were determined.Microscopic data and counting of the circulating cells revealed increasing numbers of material-surface adherent platelets with increasing agitation speed. Also, activation of the platelets was substantially increased when tested under the high shear conditions (P-Selectin levels, PFA-100 closure times). At low agitation speed, the platelet densities did not differ between the three materials. Tested at the high agitation speed, lowest platelet densities were observed on PDMS, intermediate levels on PET and highest on PTFE. While activation of the circulating platelets was affected by the implant surfaces in a similar manner, PFA closure times did not reflect this trend.Differences in the thrombogenicity of the studied polymers were more pronounced when tested at high agitation speed due to the induced shear stresses. Testing under varying shear stresses, thus, led to a different evaluation of the implant thrombogenicity, which emphasizes the need for testing under various flow conditions. Our data further confirmed earlier findings where the same reference implants were tested under static (and not dynamic) conditions and with fresh human platelet rich plasma instead of whole blood. This supports that the application of common reference materials may improve inter-study comparisons, even under varying test conditions.

Diagnostic challenges of inherited mild bleeding disorders: a bait for poorly explored clinical and basic research

The best-known inherited mild bleeding disorders (MBDs), i.e. type 1 von Willebrand disease (VWD), platelet function disorders (PFDs), and mild to moderate clotting factor deficiencies, are characterized clinically by mucocutaneous bleeding, and, although they are highly prevalent, still pose difficult diagnostic problems. These include establishing the pathological nature of bleeding, and the uncertainties surrounding the clinical relevance of laboratory results. Furthermore, the high frequency of bleeding symptoms in the normal population and the subjective appraisal of symptoms by patients or parents makes elucidating the pathological nature of bleeding difficult. Standardized bleeding assessment tools and semiquantitative bleeding scores (BSs) help to discriminate normal from abnormal bleeding. However, as most MBDs have similar bleeding patterns, for example, bleeding sites, frequency, and severity, BSs are of little help for diagnosing specific diseases. Global tests of primary hemostasis (bleeding time; PFA-100/200) lack sensitivity and, like BSs, are not disease-specific. Problems with the diagnosis of type 1 VWD and PFD include assay standardization, uncertain definition of von Willebrand factor cut-off levels, and the lack of universal diagnostic criteria for PFD. Regarding clotting factor deficiencies, the bleeding thresholds of some coagulation factors, such as factor VII and FXI, are highly variable, and may lead to misinterpretation of the clinical relevance of mild to moderate deficiencies. Remarkably, a large proportion of MBDs remain undiagnosed even after comprehensive and repeated laboratory testing. These are tentatively considered to represent bleeding of undefined cause, with clinical features indistinguishable from those of classical MBD; the pathogenesis of this is probably multifactorial, and unveiling these mechanisms should constitute a fertile source of translational research.

High-throughput elucidation of thrombus formation reveals sources of platelet function variability

In combination with microspotting, whole-blood microfluidics can provide high-throughput information on multiple platelet functions in thrombus formation. Based on assessment of the inter- and intra-subject variability in parameters of microspot-based thrombus formation, we aimed to determine the platelet factors contributing to this variation. Blood samples from 94 genotyped healthy subjects were analyzed for conventional platelet phenotyping: i.e. hematologic parameters, platelet glycoprotein (GP) expression levels and activation markers (24 parameters). Furthermore, platelets were activated by ADP, CRP-XL or TRAP. Parallel samples were investigated for whole-blood thrombus formation (6 microspots, providing 48 parameters of adhesion, aggregation and activation). Microspots triggered platelet activation through GP Ib-V-IX, GPVI, CLEC-2 and integrins. For most thrombus parameters, inter-subject variation was 2-4 times higher than the intra-subject variation. Principal component analyses indicated coherence between the majority of parameters for the GPVI-dependent microspots, partly linked to hematologic parameters, and glycoprotein expression levels. Prediction models identified parameters per microspot that were linked to variation in agonist-induced α_IIbβ₃ activation and secretion. Common sequence variation of GP6 and FCER1G, associated with GPVI-induced α_IIbβ₃ activation and secretion, affected parameters of GPVI-and CLEC-2-dependent thrombus formation. Subsequent analysis of blood samples from patients with Glanzmann thrombasthenia or storage pool disease revealed thrombus signatures of aggregation-dependent parameters that were subject-dependent, but not linked to GPVI activity. Taken together, this high-throughput elucidation of thrombus formation revealed patterns of inter-subject differences in platelet function, which were partly related to GPVI-induced activation and common genetic variance linked to GPVI, but also included a distinct platelet aggregation component.

A Randomized, Placebo-Controlled, Multiple-Ascending-Dose Study to Assess the Safety, Tolerability, Pharmacokinetics, and Pharmacodynamics of the Soluble Guanylate Cyclase Stimulator Praliciguat in Healthy Subjects

Nitric oxide (NO)-soluble guanylate cyclase (sGC)-cyclic guanosine monophosphate (cGMP) signaling is central to the regulation of several physiological processes, including blood flow and inflammation. Deficient NO signaling is implicated in multiple diseases. sGC stimulators are small molecules that enhance sGC activity, particularly in combination with NO. In a randomized, placebo-controlled phase 1 study, the safety, tolerability, pharmacokinetics, and pharmacodynamics of multiple ascending doses of the sGC stimulator praliciguat were assessed in 44 healthy adults. Four cohorts of 11 subjects (8 praliciguat, 3 placebo) received once-daily praliciguat for 14 days before up-titrating for 7 days (treatment sequences: 15/30 mg, 20/40 mg, 30/40 mg, and weight-based). All doses were tolerated. No serious or severe adverse events (AEs) were reported. The most common AEs in praliciguat recipients were headache and symptoms consistent with blood pressure (BP) lowering/vasodilation. There were no laboratory, vital sign, electrocardiographic, or platelet function findings indicative of a safety concern. Pharmacokinetics were dose proportional, with an effective half-life of 24-37 hours, supporting once-daily dosing. Praliciguat produced dose-related increases in plasma cGMP consistent with stimulation of sGC. Repeated once-daily dosing showed sustained decreases in BP. Results support evaluation of praliciguat for the treatment of conditions associated with deficient NO signaling.