Diagnosis of inherited platelet function disorders: guidance from the SSC of the ISTH

Congenital platelet disorders and health status-related quality of life

BACKGROUND

Patients with congenital blood platelet disorders (CPDs) demonstrate a predominantly mucocutaneous bleeding tendency. Repeated bleeds throughout life can have a significant impact on health status-related quality of life (HR-QoL), but few studies have investigated HR-QoL in patients with CPDs.

OBJECTIVES

To determine HR-QoL in patients with suspected or confirmed CPDs as compared with the general Dutch population and to assess the association between bleeding phenotype and HR-QoL.

METHODS

Data were derived from the Thrombocytopathy in the Netherlands (TiN) study, a cross-sectional study of individuals suspected for a congenital platelet defect. TiN patients with an increased ISTH Bleeding Assessment Tool (ISTH-BAT) score (>3 in men and > 5 in women) were included for analysis. HR-QoL was assessed with the Short Form (SF)-36 survey. Bleeding symptoms were evaluated with the ISTH-BAT, resulting in a bleeding score.

RESULTS

One hundred fifty-six patients were analyzed, of whom 126 (81%) were women. Sixty-two patients (40%) had a confirmed CPD. Compared to the general Dutch population, patients with a suspected or confirmed CPD reported decreased physical functioning, limitations in daily activities due to physical health problems, limitations in social activities, decreased energy levels and fatigue, pain, and lower general health status. HR-QoL was not correlated with the ISTH-BAT score and was similar in patients with a confirmed CPD and those in whom a CPD could not be diagnosed.

CONCLUSION

A bleeding tendency in patients with a suspected or confirmed CPD significantly impacts HR-QoL, independent of a confirmed explanatory diagnosis.

Severe postpartum haemorrhage as first presenting symptom of an inherited bleeding disorder

INTRODUCTION

Postpartum haemorrhage (PPH) is the major cause of maternal death worldwide. Haemostatic abnormalities are independently associated with a significantly increased risk for severe PPH. In this study, the value of haemostatic evaluation in women with severe PPH was explored.

AIM

To investigate the occurrence of previously unknown inherited bleeding disorders in women with severe PPH.

METHODS

Women with severe PPH (blood loss of ≥2000 mL) between 2011 and 2017, referred to the haematology outpatient clinic for haemostatic evaluation, were retrospectively included. A bleeding disorder was diagnosed based on (inter)national guidelines, or when having a clear bleeding phenotype, not fulfilling any diagnostic criteria or laboratory abnormalities, this being classified as Bleeding of Unknown Cause (BUC). Logistic regression was used to model the association between diagnosis and obstetrical causes and risk factors for PPH.

RESULTS

In total, 85 women with PPH were included. In 23% (n = 16), a mild bleeding disorder was diagnosed, including low von Willebrand factor (Low VWF 8/16), platelet function disorders (PFD 5/16), BUC (2/16) and von Willebrand disease type 1 (1/16). No significant associations were found between obstetrical causes or risk factors for PPH and the presence of a bleeding disorder.

CONCLUSION

In 23% of women with severe PPH, a mild bleeding disorder was diagnosed, independent of obstetrical causes or risk factors for PPH. This implies that severe PPH can be the first clinical symptom of an inherited bleeding disorder. Therefore, to optimize clinical management, haemostatic evaluation after severe PPH is recommended.

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.

Antithrombotic prophylaxis for surgery-associated venous thromboembolism risk in patients with inherited platelet disorders. The SPATA-DVT Study

Major surgery is associated with an increased risk of venous thromboembolism (VTE), thus the application of mechanical or pharmacologic prophylaxis is recommended. The incidence of VTE in patients with inherited platelet disorders (IPD) undergoing surgical procedures is unknown and no information on the current use and safety of thromboprophylaxis, particularly of low-molecular-weight-heparin in these patients is available. Here we explored the approach to thromboprophylaxis and thrombotic outcomes in IPD patients undergoing surgery at VTE-risk participating in the multicenter SPATA study. We evaluated 210 surgical procedures carried out in 155 patients with well-defined forms of IPD (VTE-risk: 31% high, 28.6% intermediate, 25.2% low, 15.2% very low). The use of thromboprophylaxis was low (23.3% of procedures), with higher prevalence in orthopedic and gynecological surgeries, and was related to VTE-risk. The most frequently employed thromboprophylaxis was mechanical and appeared to be effective, as no patients developed thrombosis, including patients belonging to the highest VTE-risk classes. Low-molecular-weight-heparin use was low (10.5%) and it did not influence the incidence of post-surgical bleeding or of antihemorrhagic prohemostatic interventions use. Two thromboembolic events were registered, both occurring after high VTE-risk procedures in patients who did not receive thromboprophylaxis (4.7%). Our findings suggest that VTE incidence is low in patients with IPD undergoing surgery at VTE-risk and that it is predicted by the Caprini score. Mechanical thromboprophylaxis may be of benefit in patients with IPD undergoing invasive procedures at VTE-risk and low-molecular-weight-heparin should be considered for major surgery.

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.

Bleeding Symptoms and von Willebrand Factor Levels: 30-Year Experience in a Tertiary Care Center

Correlations between bleeding symptoms and von Willebrand factor (VWF) levels may help to predict hemorrhagic severity in the Westerners with von Willebrand disease (VWD), but data in Asians are lacking. In this study, Thai patients with VWF levels <50 IU/dL without any secondary causes were enrolled from 1988 to 2018 to determine the relationship between VWF levels and hemorrhagic manifestations. According to the current concept, we reclassified VWD and low VWF by VWF levels ≤30 and 30 to 50 IU/dL, respectively. Type 2 VWD was diagnosed if VWF activity to antigen ratio was ≤0.6. Bleeding severity was determined by the condensed MCMDM-1VWD bleeding score (BS). Among 83 patients, VWF activities showed negative correlations with BS (P = .001), which were higher in type 2 (median: 7, interquartile range [IQR]: 5-11) compared with type 1 VWD (median: 3, IQR: 2-4) and low VWF (median: 4, IQR: 2-8). Bleeding symptoms were indistinguishable between type 1 VWD and low VWF using the 30 IU/dL cutoff point. However, VWF ristocetin cofactor activity or gain-of-function mutant glycoprotein Ib binding activity <36.5 IU/dL and VWF collagen binding activity <34.5 IU/dL could predict increased bleeding risk (BS ≥3) by 92.3% specificity and 70.0% sensitivity (P < .0001).

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.

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.

Acquired platelet function disorders

The possibility of an acquired platelet function disorder should be considered in patients who present with recent onset muco-cutaneous bleeding. Despite the availability of newer and faster platelet function assays, light transmission aggregometry (LTA) remains the preferred diagnostic test. This review examines and discusses the causes of acquired platelet dysfunction; most commonly drugs, dietary factors, medical disorders and procedures. In addition to well-known antiplatelet therapies, clinicians should be alert for newer drugs which can affect platelets, such as ibrutinib. There is little clinical trial evidence to guide the management of acquired platelet function defects, but we summarise commonly employed strategies, which include addressing the underlying cause, antifibrinolytic agents, desmopressin infusions, and in selected patients, platelet transfusions.

Perioperative Hemostatic Management of a Pediatric Patient with Glanzmann Thrombasthenia Undergoing Osteoplastic Craniotomy and Hematoma Removal: A Case Report

Glanzmann thrombasthenia is an uncommon hereditary disease that involves an abnormal platelet function leading to complicated hemostatic problems. In situations of anticipated hemorrhage, irradiated apheresed platelets are the first line of treatment. In addition, a combination of recombinant factor VIIa and an antifibrinolytic agent such as tranexamic acid can be utilized to minimize bleeding. Here we are present stable management of a pediatric patient with Glanzmann thrombasthenia admitted for traumatic epidural hematoma removal. Due to the condition of the operation site, some blood loss was unavoidable. However, hemostasis was successfully controlled, and the patient was discharged without additional complications.

Inherited Platelet Disorders: A Modern Approach to Evaluation and Treatment

The inherited platelet disorders are a heterogeneous group of disorders that can be pleotropic in their clinical presentations. They may present with variable platelet counts and bleeding, making their diagnosis difficult. New diagnostic tools range from flow cytometric platelet function assessments to next-generation sequencing. Several platelet disorders may now be treated with gene therapy or bone marrow transplant. Improved understanding of the molecular and biologic mechanisms of the inherited platelet disorders may lead to novel targeted therapies.

Bleeding Disorders in Adolescents with Heavy Menstrual Bleeding: The Queensland Statewide Paediatric and Adolescent Gynaecology Service

STUDY OBJECTIVE

Heavy menstrual bleeding (HMB) is a common gynecological complaint among young women with up to 40% having experienced HMB. Bleeding disorders are increasingly being recognized in adolescents and young adults with HMB. The aim of this study was to determine the prevalence of bleeding disorders in adolescents with HMB, among patients who presented to the Queensland Statewide Paediatric and Adolescent Gynaecology Service between July 2007 and July 2017. DESIGN, SETTING, PARTICIPANTS, INTERVENTIONS, AND MAIN OUTCOME MEASURES: The study was a retrospective review of 124 female adolescents aged 8 to 18 years with HMB who presented to the Queensland Paediatric and Adolescent Gynaecology Service, Brisbane, Australia. The primary outcome measure was diagnosis of a bleeding disorder, with secondary outcomes including iron deficiency and/or anemia and treatment modalities.

RESULTS

Screening for bleeding disorders was performed in 77/124 (62.1%) of patients with HMB. Twenty-seven adolescents were diagnosed with a bleeding disorder, giving a prevalence of 27/124 (21.7%) in those with HMB, and 27/77 (35%) with HMB who were screened. Of these 35%, von Willebrand disease was the most common bleeding disorder, found in 14/27 (51.6%), followed by inherited platelet function disorders diagnosed in 9/27 (33.3%), thrombocytopenia (inherited or acquired) in 3/27 (11.1%), and Factor IX deficiency in 1/27 (3.7%). Iron deficiency and/or anemia was diagnosed in 53/107 (49.5%) of patients with HMB who were screened for this, and 19/27 (70.3%) of those diagnosed with a bleeding disorder.

CONCLUSION

Adolescents with HMB who present to a tertiary pediatric and adolescent gynecology service should be screened for bleeding disorders, because of the considerably high prevalence in this at-risk population.

Simplifying the diagnosis of inherited platelet disorders? The new tools do not make it any easier

The molecular causes of many inherited platelet disorders are being unraveled. Next-generation sequencing facilitates diagnosis in 30% to 50% of patients. However, interpretation of genetic variants is challenging and requires careful evaluation in the context of a patient's phenotype. Before detailed testing is initiated, the treating physician and patient should establish an understanding of why testing is being performed and discuss potential consequences, especially before testing for variants in genes associated with an increased risk for hematologic malignancies.

Diagnosis of hereditary platelet disorders in the era of next-generation sequencing: "primum non nocere"

Inherited platelet disorders can affect "only platelets", occur as a "syndromic phenotype" or be associated with "increased risk of hematological malignancies". Genetic testing is attractive for diagnosis of inherited platelet disorders. However, many physicians who refer patient blood for genetic testing are unaware of the association of certain inherited platelet disorders with other risks. Inherited platelet disorders associated with minor-moderate bleeding rarely cause patient distress. In contrast, identification of a mutation associated with an increased risk of leukemia may cause a major psychological disease burden, without offsetting the beneficial impact on management. Guidelines recommend postponing genetic testing "until the patient reaches adulthood or at least until the child is mature enough to participate in decision making". In our opinion, outside research, (genetic) testing in children with inherited platelet disorders should only be performed if it influences management. In adults, genes causing inherited platelet disorders associated with an increased risk of hematological malignancies should only be tested after obtaining explicit informed consent.

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.

A simplified flow cytometric method for detection of inherited platelet disorders-A comparison to the gold standard light transmission aggregometry

Background

Flow cytometric platelet activation has emerged as an alternative diagnostic test for inherited platelet disorders. It is, however, labor intensive and few studies have directly compared the performance of flow cytometric platelet activation (PACT) to light transmission aggregometry (LTA). The aims of this study were 1/ to develop a simplified flow cytometric platelet activation assay using microtiter plates and 2/ to correlate the outcome to gold standard method LTA, and to clinical bleeding assessment tool scores (BAT score).

Methods

The PACT method was developed in microtiter plates using adenosine diphosphate (ADP), collagen-derived peptide (CRP-XL) and thrombin receptor activator for peptide 6 (TRAP-6) as agonists. Antibodies against GPIIb-IIIa activation epitope (PAC1), P-selectin (CD62P) and lysosome-associated membrane glycoprotein 3 (LAMP3; CD63) were used as platelet activation markers. Sixty-six patients referred to the coagulation unit for bleeding symptoms were included in this single-center observational study. Platelet activation was determined by PACT and LTA. The results of both methods were correlated to BAT score.

Results

A two-by-two analysis using Cohen’s kappa analysis gave moderate agreement between LTA and PACT (82%, kappa = 0.57), when PACT analysis with ADP and CRP-XL was compared to LTA. Using LTA as reference method, positive predictive value was 70% and negative predictive value was 87%. A substantial number of patients had high BAT score and normal LTA and PACT results. Patients with abnormal LTA or PACT results had higher BAT score than patients with normal results, but the difference was not significant.

Conclusions

The performance in microtiter plates simplified the PACT method and enabled analysis of more patients at the same time. Our results indicate that with modification of the current PACT assay, a higher negative predictive value can be obtained. Furthermore, with comparable result to LTA the PACT could be used as a screening assay for inherited platelet disorders.

Use of Targeted High-Throughput Sequencing for Genetic Classification of Patients with Bleeding Diathesis and Suspected Platelet Disorder

Inherited platelet disorders (IPD) form a rare and heterogeneous disease entity that is present in about 8% of patients with non-acquired bleeding diathesis. Identification of the defective cellular pathway is an important criterion for stratifying the patient's individual risk profile and for choosing personalized therapeutic options. While costs of high-throughput sequencing technologies have rapidly declined over the last decade, molecular genetic diagnosis of bleeding and platelet disorders is getting more and more suitable within the diagnostic algorithms. In this study, we developed, verified, and evaluated a targeted, panel-based next-generation sequencing approach comprising 59 genes associated with IPD for a cohort of 38 patients with a history of recurrent bleeding episodes and functionally suspected, but so far genetically undefined IPD. DNA samples from five patients with genetically defined IPD with disease-causing variants in WAS , RBM8A , FERMT3 , P2YR12 , and MYH9 served as controls during the validation process. In 40% of 35 patients analyzed, we were able to finally detect 15 variants, eight of which were novel, in 11 genes, ACTN1 , AP3B1 , GFI1B , HPS1 , HPS4 , HPS6 , MPL , MYH9 , TBXA2R , TPM4 , and TUBB1 , and classified them according to current guidelines. Apart from seven variants of uncertain significance in 11% of patients, nine variants were classified as likely pathogenic or pathogenic providing a molecular diagnosis for 26% of patients. This report also emphasizes on potentials and pitfalls of this tool and prospectively proposes its rational implementation within the diagnostic algorithms of IPD.

Flow cytometry for pediatric platelets

The ability of platelets to carry out their hemostatic function can be impaired in a wide range of inherited and acquired conditions: trauma, surgery, inflammation, pre-term birth, sepsis, hematological malignancies, solid tumors, chemotherapy, autoimmune disorders, and many others. Evaluation of this impairment is vitally important for research and clinical purposes. This problem is particularly pronounced in pediatric patients, where these conditions occur frequently, while blood volume and the choice of blood collection methods could be limited. Here we describe a simple flow cytometry-based screening method of comprehensive whole blood platelet function testing that was validated for a range of pediatric and adult samples (n = 31) in the hematology hospital setting including but not limited to: classic inherited platelet function disorders (Glanzmann's thrombasthenia; Bernard-Soulier, Wiscott-Aldrich, and Hermasky-Pudlak syndromes, MYH9-dependent thrombocytopenia), healthy and pre-term newborns, acute and chronic immune thrombocytopenia, chronic lympholeukemia, effects of therapy on platelet function, etc. The method output includes levels of forward and side scatter, levels of major adhesion and aggregation glycoproteins Ib and IIb-IIIa, active integrins' level based on PAC-1 binding, major alpha-granule component P-selectin, dense granule function based on mepacrine uptake and release, and procoagulant activity quantified as a percentage of annexin V-positive platelets. This analysis is performed for both resting and dual-agonist-stimulated platelets. Preanalytical and analytical variables are provided and discussed. Parameter distribution within the healthy donor population for adults (n = 72) and children (n = 17) is analyzed.

How I investigate for bleeding disorders

INTRODUCTION

Laboratory investigations for bleeding disorders are warranted when an individual has a personal and/or family history of bleeding, and/or laboratory findings that suggest the possibility of an inherited or acquired bleeding disorder.

METHODS

This review summarizes author's experience with ordering and reporting on diagnostic investigations for common and rare bleeding disorders, with consideration of recent articles on diagnosing bleeding disorders. An updated strategy is presented for investigating common and rare, congenital and acquired bleeding disorders.

RESULTS

An investigation of a suspected bleeding disorder requires a practical strategy that considers the clinical problem to be investigated, the pretest probability of true-positive and false-positive findings, the investigations can be performed locally or in a reference laboratory and limit the number of blood samples required to establish a diagnosis. It is often advantageous to simultaneously test for von Willebrand disease and platelet function disorders, and for coagulation defects, including fibrinogen disorders. An investigation for rarer bleeding disorders, including those affecting factor XIII, α₂ antiplasmin, and plasminogen activator inhibitor-1, is appropriate when faced with a severe congenital or acquired bleeding problem that cannot be explained by the initial diagnostic investigations.

CONCLUSION

An organized strategy for investigating bleeding disorders that consider important issues, confirms abnormal findings, encourages proper interpretation of the results, and provides a helpful framework for assessing both common and rare causes of bleeding.

Preoperative screening for bleeding disorders: A comprehensive laboratory assessment of clinical practice

BACKGROUND

Patients with mild bleeding disorders are at risk of perioperative bleeding, but screening for these disorders remains challenging.

OBJECTIVES

We aimed to assess the prevalence of hemostatic abnormalities in patients with and without reported bleeding symptoms on a preoperative questionnaire, consisting of guideline-proposed questions, and appraised the diagnostic value of several screening modalities for the identification of patients with hemostatic abnormalities.

METHODS

In this observational study, 240 patients with and 95 patients without bleeding symptoms on the preoperative questionnaire were included. Patients with known bleeding disorders, antithrombotic drugs, thrombocytopenia, and anemia were excluded. Preoperatively, all patients underwent elaborate hemostatic testing. Hemostatic abnormalities were defined as coagulation, vWF, or fibrinolysis factor levels below reference range and platelet function defects. Screening modalities included the ISTH Bleeding Assessment Tool (ISTH-BAT), PT, aPTT, TT, Euglobulin Lysis Time (ELT), and Platelet Function Analyser (PFA).

RESULTS

In 21 of 240 (8.8%) patients reporting bleeding symptoms, hemostatic abnormalities were found, including 7 reduced coagulation factor levels, 10 platelet function abnormalities, and 4 reduced vWF levels. In comparison, 10 of 95 (10.5%) patients not reporting bleeding symptoms had abnormalities. The ISTH-BAT could not identify patients with abnormalities, while PT, aPTT, TT, ELT, and PFA had high specificity but low sensitivity to detect abnormalities.

CONCLUSIONS

The prevalence of hemostatic abnormalities in both patients with and without reported bleeding symptoms was 9%-10%. This suggests that the guideline-based questionnaire cannot differentiate between patients with and without abnormalities, while the discriminative power of the screening modalities is also limited.

High-throughput sequencing for diagnosing platelet disorders: lessons learned from exploring the causes of bleeding disorders

Inherited platelet disorders (IPDs) are a heterogeneous group of disorders caused by multiple genetic defects. Obtaining a molecular diagnosis for IPD patients using a phenotype- and laboratory-based approach is complex, expensive, time-consuming, and not always successful. High-throughput sequencing (HTS) methods offer a genotype-based approach to facilitate molecular diagnostics. Such approaches are expected to decrease time to diagnosis, increase the diagnostic rate, and they have provided novel insights into the genotype-phenotype correlation of IPDs. Some of these approaches have also focused on the discovery of novel genes and unexpected molecular pathways which modulate megakaryocyte and platelet biology were discovered. A growing number of genetic defects underlying IPDs have been identified and we will here provide an overview of the diverse molecular players. Screening of these genes will deliver a genetic diagnosis for about 40%-50% of the IPDs patients and we will compare different HTS applications that have been developed. A brief focus on gene variant interpretation and classification in a diagnostic setting will be given. Although it is true that successes in diagnostics and gene discovery have been reached, a large fraction of patients still remains without a conclusive diagnosis. In these patients, the sum of non-diagnostic variants in known genes or in potential novel genes might only be proven informative in future studies with larger patient cohorts and by data sharing among the diverse genome medicine initiatives. Finally, we still do not understand the role of the non-coding genome space for IPDs.

Application of High-Throughput Sequencing in the Diagnosis of Inherited Thrombocytopenia

Inherited thrombocytopenia is a group of hereditary diseases with a reduction in platelet count as the main clinical manifestation. Clinically, there is an urgent need for a convenient and rapid diagnosis method. We introduced a high-throughput, next-generation sequencing (NGS) platform into the routine diagnosis of patients with unexplained thrombocytopenia and analyzed the gene sequencing results to evaluate the value of NGS technology in the screening and diagnosis of inherited thrombocytopenia. From a cohort of 112 patients with thrombocytopenia, we screened 43 patients with hereditary features. For the blood samples of these 43 patients, a gene sequencing platform for hemorrhagic and thrombotic diseases comprising 89 genes was used to perform gene detection using NGS technology. When we combined the screening results with clinical features and other findings, 15 (34.9%) of 43patients were diagnosed with inherited thrombocytopenia. In addition, 19 pathogenic variants, including 8 previously unreported variants, were identified in these patients. Through the use of this detection platform, we expect to establish a more effective diagnostic approach to such disorders.

Inherited platelet disorders : Management of the bleeding risk

Inherited platelet disorders are rare bleeding syndromes due to either platelet function abnormalities or thrombocytopenia which may be associated with functional defects. The haemorrhagic symptoms observed in these patients are mostly muco-cutaneous and of highly variable severity. Although 30 to 50% of the platelet disorders are still of unknown origin, the precise diagnosis of these pathologies by specialized laboratories together with haemorrhagic scores enables an assessment of the risk of bleeding in each patient. Depending on the diagnostic elements collected, an appropriate medical procedure can be proposed for each situation: scheduled or emergency surgical interventions and pregnancy follow-up. The pathologies most at risk correspond to Glanzmann's thrombasthenia, Bernard-Soulier syndrome, severe thrombocytopenia (<40,000 platelets/μL) and signalling protein abnormalities affecting the activation of GPIIb-IIIa, a membrane glycoprotein essential for platelet aggregation. For these particular patients, in whom the risk of bleeding can be increased by a factor of 40, management protocols during surgical procedures are generally based on the use of conventional platelet concentrates, for both prophylaxis and the control of active bleeding. The perinatal period in women with platelet disorders and their new-born also require special attention. Indeed, beyond unpredictable delivery haemorrhages, bleeding requiring a blood transfusion is observed after delivery in more than 50% of women with Glanzmann's thrombastenia or Bernard-Soulier syndrome.

Inherited platelet functional disorders: General principles and practical aspects of management

Platelets are a critical component for effecting hemostasis and wound healing. Disorders affecting any platelet pathway mediating adhesion, activation, aggregation and procoagulant surface exposure can result in a bleeding diathesis. Specific diagnosis even with advanced techniques which are unavailable to most centers is often difficult. Inherited platelet function disorders therefore represent a heterogeneous and complex collection of disorders with a spectrum of bleeding severity, from relatively mild (and easily missed or misdiagnosed) to severe bleeding phenotype with salient diagnostic features. We advocate the use of bleeding assessment tools to help identification of patients and more importantly for assessment of individual patient bleeding phenotype to guide management decisions for treating and preventing bleeding. The complex management of these patients is best coordinated in a multidisciplinary comprehensive care clinic setting expert in managing bleeding disorders and associated complications, with particular attention to the physical and psychosocial health of patients and their families. Depending on the bleeding phenotype, the location and severity of bleeding, and the nature of an invasive procedure, available treatment modalities range from conservative measures using local pressure, topical thrombin, fibrin sealant, antifibrinolytics etc. to the use of systemic haemostatics such as desmopressin (DDAVP), platelets and recombinant human activated factor VII (rFVIIa). This review will provide opinions on the practical aspects and general management of inherited platelet function disorders, with discussion on the mechanism of action, and the pros and cons of various hemostatic agents. Finally, the prospect of curative treatment for patients with severe bleeding phenotype refractory to available treatments and with poor quality of life will be briefly discussed.

Platelet aggregation measured by single-platelet counting and using PFA-100 devices

Platelets play a crucial role in haemostasis and thrombosis and evaluation of platelet function in vitro, in particular platelet aggregation responses, has been one of the most common and useful ways of evaluating the risk of bleeding and thrombotic events and assessing the effects of various compounds and conditions on platelets. Traditional approaches to assessing platelet aggregation require specialised equipment and trained laboratory personnel and have other limitations. Studying platelet aggregation in whole blood offers a more physiologically relevant measurement. Additionally, certain approaches could be more widely available than in specialised laboratories. Here we summarise the application of the platelet function analyser (PFA-100), an accessible first point-of-care test for platelet function in whole blood, and the less established, but promising approach of assessing platelet aggregation by single-platelet counting that can also be performed in whole blood. The possibilities of a wider and more accessible application of the latter methodology are also discussed.

Validation of flow cytometric analysis of platelet function in patients with a suspected platelet function defect

Essentials The diagnosis of mild platelet function disorders (PFDs) is challenging. Validation of flow cytometric testing in patients with suspected PFDs is required. Flow cytometry has added value to light transmission aggregometry (LTA) in diagnosis of PFDs. There is fair agreement in diagnosing PFDs between LTA and flow cytometry.

SUMMARY

Background Light transmission aggregometry (LTA) is the most commonly used test for the diagnosis of platelet function disorders (PFDs), but has moderate sensitivity for mild PFDs. Flow cytometry has been recommended for additional diagnostics of PFDs but is not yet standardized as a diagnostic test. We developed a standardized protocol for flow cytometric analysis of platelet function that measures fibrinogen binding and P-selectin expression as platelet activation markers in response to agonist stimulation. Objectives To determine the additional value of flow cytometric platelet function testing to standard LTA screening in a cross-sectional cohort of patients with a suspected PFD. Methods Platelet function was assessed with flow cytometry and LTA in 107 patients suspected of a PFD in whom von Willebrand disease and coagulation factor deficiencies were excluded. Both tests were compared in terms of agreement and discriminative ability for diagnosing patients with PFDs. Results Out of 107 patients, 51 patients had an elevated bleeding score; 62.7% of the patients had abnormal platelet function measured with flow cytometry and 54.2% of the patients were abnormal based on LTA. There was fair agreement between LTA and flow cytometry (κ = 0.32). The discriminative ability of flow cytometric analysis in patients with an elevated bleeding score was good (AUC 0.82, 0.74-0.90), but moderate for LTA (AUC 0.70, 0.60-0.80). Both tests combined had a better discriminative ability (AUC 0.87, 0.80-0.94). Conclusion Flow cytometric analysis of platelet function has added value in diagnostics of PFDs in patients with unexplained bleeding tendency.

Electron microscopy examination of platelet whole mount preparations to quantitate platelet dense granule numbers: Implications for diagnosing suspected platelet function disorders due to dense granule deficiency

INTRODUCTION

Dense granule (DG) deficiency (DGD) is a feature of some platelet function disorders (PFD) with a prevalence similar to von Willebrand disease. Most laboratories assess for DGD using whole mount platelet preparations and electron microscopy (EM). We evaluated our experiences with this test and associations between DGD and bleeding.

METHODS

Dense granule EM records for 2006-2017 were examined for patients and simultaneously tested controls, and for an overlapping PFD study cohort to evaluate findings and their relationship to bleeding.

RESULTS

More patient than control samples had reduced DG counts (6.5% vs 0.3%, P < .01). DG counts showed no relationship to age or mean platelet volume and had acceptable within-subject variability that was higher for DGD than control participants (28% vs 12%). Repeat tests confirmed DGD in all persons with initial DG counts <4.0/platelet, but not in those with less severe reductions (4.0-4.8 DG/platelet) or normal DG counts (≥4.9 DG/platelet). Aggregometry and adenosine triphosphate release tests, respectively, had only ~52% and 70% sensitivity for DGD. Confirmed DGD by EM was associated with higher bleeding scores and a bleeding disorder.

CONCLUSION

Whole mount EM is useful for the evaluation of suspected PFD due to DGD and detects abnormalities associated with bleeding.

High proportion of patients with bleeding of unknown cause in persons with a mild-to-moderate bleeding tendency: Results from the Vienna Bleeding Biobank (VIBB)

INTRODUCTION

Data on clinical characteristics and the prevalence of underlying coagulopathies in patients with mild-to-moderate bleeding disorders (MBDs) are scarce.

AIM

We established the Vienna Bleeding Biobank (VIBB) to characterize and thoroughly investigate Austrian patients with MBDs.

RESULTS

Four hundred eighteen patients (female = 345, 82.5%) were included. A platelet function defect (PFD) was diagnosed in 26 (6.2%) and a possible PFD in 30 (7.2%) patients. Eight patients (1.9%) were diagnosed with von Willebrand disease (VWD) (type 1 n = 6; type 2 n = 2), and 29 patients had low VWF (30-50 IU/dL). Deficiencies in factor VIII, IX, XI or XIII were found in 11 (2.6%), 3 (0.7%), 3 (0.7%) and 1 patient(s), 2 patients had dysfibrinogenaemia, and further 2 had possible PFD and FXI deficiency. Probable causal mutations were detected in 8 of 11 patients with FVIII deficiency, 2 of 3 patients with FIX deficiency and 2 of 8 patients with VWD. Three hundred three patients (72.5%) had normal results in the coagulation assays and were categorized as patients with bleeding of unknown cause (BUC). The bleeding score did not differ between patients with and without established diagnosis. A diagnosis of a bleeding disorder was more frequently made in men than in women (49.3% vs 22.9%). Male sex (OR 3.55, 95% CI: 2.02-6.22; P < .001) and blood group 0 (OR 1.86, 95% CI: 1.17-2.94; P = .008) were independently associated with diagnosis of a bleeding disorder.

CONCLUSION

The high rate of patients with BUC despite in-depth haemostatic assessment underlines the incompleteness of available routine laboratory tests. Males with MBDs were more likely to be diagnosed with an established bleeding disorder than females.

Standardization and reference ranges for whole blood platelet function measurements using a flow cytometric platelet activation test

Introduction

Platelet function testing with flow cytometry has additional value to existing platelet function testing for diagnosing bleeding disorders, monitoring anti-platelet therapy, transfusion medicine and prediction of thrombosis. The major challenge is to use this technique as a diagnostic test. The aim of this study is to standardize preparation, optimization and validation of the test kit and to determine reference values in a population of 129 healthy individuals.

Methods

Platelet function tests with 3 agonists and antibodies against P-selectin, activated αIIbβ3 and glycoprotein Ib (GPIb), were prepared and stored at -20°C until used. Diluted whole blood was added and platelet activation was quantified by the density of activation markers, using flow cytometry. Anti-mouse Ig κ particles were included to validate stability of the test and to standardize results. Reference intervals were determined.

Results

Blood stored at room temperature (RT) for up to 4h after blood donation and preheated/tested at 37°C resulted in stable results (%CV<10%), in contrast to measuring at RT. The intra-assay %CV was <5%. Incubation of anti-mouse Ig κ particles with antibodies stored for up to 12 months proved to give a stable fluorescence. The inter-individual variation measured in the 129 individuals varied between 23% and 37% for P-selectin expression and αIIbβ3 activation, respectively.

Conclusions

The current study contributes to the translation of flow cytometry based platelet function testing from a scientific tool to a diagnostic test. Platelet function measurements, using prepared and stored platelet activation kits, are reproducible if executed at 37°C. The reference ranges can be validated in clinical laboratories and ongoing studies are investigating if reduced platelet reactivity in patients with bleeding complications can be detected.

A review of platelet secretion assays for the diagnosis of inherited platelet secretion disorders

Measurement of platelet granule release to detect inherited platelet secretion disorders (IPSDs) is essential for the evaluation of patients with abnormal bleeding and is necessary to distinguish which granule sub-types are affected and whether there is abnormal granule bio-synthesis or secretion. The radioactive serotonin incorporation and release assay, described before 1970, is still considered the “gold standard” test to assess platelet δ-granule release, although is unsuitable for clinical diagnostic laboratories. Luciferin-based assays, such as lumiaggregometry, are the most widely performed alternatives, although these methods do not distinguish defects in δ-granule biosyn-thesis from defects in secretion. Platelet α-granule release is commonly evaluated using flow cytometry by measuring surface exposure of P-selectin after platelet activation. However, this assay has poor sensitivity for some α-granule disorders. Only few studies have been published with more recently developed assays and no critical reviews on these methods are available. In this review, we describe the rationale for developing robust and accurate laboratory tests of platelet granule release and describe the characteristics of the currently available tests. We identify an unmet need for further systematic evaluation of new assays and for standardisation of methodologies for clinical diagnostic laboratories.

Mean platelet diameter measurements to classify inherited thrombocytopenias

INTRODUCTION

Mean platelet volume (MPV) assists the differential diagnosis of inherited thrombocytopenia (IT) but lacks standardisation and varies between automated analysers. Classification of IT based on mean platelet diameter (MPD) has been proposed by an international collaborative study but has not been validated.

METHODS

To assess the applicability of MPD to classify forms of IT, digital images of blood films from patients with established genetic causes for IT were generated, and the MPD measured (ZEISS Axio-scanner and Image J software) by a blinded reviewer. Comparison was made to the proposed classification system.

RESULTS

Mean platelet volume was measured in thrombocytopenia with different genetic aetiologies, bilallelic BSS (bBSS) (n = 1), monoallelic BSS (mBSS) (n = 2), MYH9-related disorders (MYH9-RD) (n = 11), GFI1B-related thrombocytopenia (RT) (n = 15), FLI1-RT (n = 2), TUBB1-RT (n = 3), ITGA2B/ITGB3-RT (n = 1), RUNX1-RT (n = 2) and controls (n = 54). bBSS and 82% of MYH9-RD samples had MPD >4 μm which correlated with "IT with giant platelets." Only 55% of samples expected in the "large platelet group" had MPD meeting the classification cut-off (MPD >3.2 μm). FLI1-RT MPD were significantly larger than expected whilst ITGA2B/ITGB3-RT MPD were smaller than proposed. MPD in FPD/AML were "normal."

CONCLUSION

Platelet MPD measurements are a useful guide to classify IT, but the time taken to record measurements may limit clinical applicability.

Screening for platelet function disorders with Multiplate and platelet function analyzer

Light transmission aggregation (LTA) is the gold standard for the diagnosis of platelet function disorders (PFDs), but it is time-consuming and limited to specialized laboratories. Whole-blood impedance aggregometry (Multiplate) and platelet function analyzer (PFA) may be used as rapid screening tools to exclude PFDs. The aim of this study is to assess the diagnostic performance of Multiplate and PFA for PFDs, as detected by LTA.Data from preoperative patients, patients referred to the hematologist for bleeding evaluation, and patients with a diagnosed bleeding disorder were used. PFDs were defined as ≥2 abnormal LTA curves. Diagnostic performance of Multiplate and PFA for detecting PFDs was expressed as sensitivity and specificity. The ability of Multiplate agonists and PFA kits to detect corresponding LTA curve abnormalities was expressed as area under the receiver operating characteristic curve. Prevalence of PFDs was 16/335 (4.8%) in preoperative patients, 10/54 (18.5%) in referred patients, and 3/25 (12%) in patients with a diagnosed bleeding disorder. In preoperative and referred patients, the sensitivity of Multiplate and PFA for detecting mild PFDs varied between 0% and 40% and AUCs for detecting corresponding LTA curve abnormalities were close to 0.50. In patients with a diagnosed bleeding disorder, both assays could detect Glanzmann thrombasthenia (GT) with sensitivity of 100% and AUCs of 0.70-1.00. Multiplate and PFA cannot discriminate between preoperative and referred patients with and without mild PFDs, meaning that they cannot be used as screening tests to rule out mild PFDs in these populations. Both Multiplate and PFA can detect GT in previously diagnosed patients.

Challenges on the diagnostic approach of inherited platelet function disorders: Is a paradigm change necessary?

Inherited platelet function disorders (IPFD) have been assessed for more than 50 years by aggregation- and secretion-based tests. Several decision trees are available intending to standardize the investigation of IPFD. A large variability of approaches is still in use among the laboratories across the world. In spite of costly and lengthy laboratory evaluation, the results have been found inconclusive or negative in a significant part of patients having bleeding manifestations. Molecular investigation of newly identified IPFD has recently contributed to a better understanding of the complexity of platelet function. Once considered "classic" IPFDs, Glanzmann thrombasthenia and Bernard-Soulier syndrome have each had their pathophysiology reassessed and their diagnosis made more precise and informative. Megakaryopoiesis, platelet formation, and function have been found tightly interlinked, with several genes being involved in both inherited thrombocytopenias and impaired platelet function. Moreover, genetic approaches have moved from being used as confirmatory diagnostic tests to being tools for identification of genetic variants associated with bleeding disorders, even in the absence of a clear phenotype in functional testing. In this study, we aim to address some limits of the conventional tests used for the diagnosis of IPFD, and to highlight the potential contribution of recent molecular tools and opportunities to rethink the way we should approach the investigation of IPFD.

Allogeneic hematopoietic cell transplantation in an adult patient with Glanzmann thrombasthenia

Glanzmann thrombasthenia is a rare bleeding disorder that can present life‐threatening bleeding. Our patients develop antiplatelet antibodies that become refractory to any pharmacological treatment. Allogeneic hematopoietic stem‐cell transplantation is the only currently curative procedure, but has major risks mainly in adult; indeed, our patient died.

Introducing high-throughput sequencing into mainstream genetic diagnosis practice in inherited platelet disorders

Inherited platelet disorders are a heterogeneous group of rare diseases, caused by inherited defects in platelet production and/or function. Their genetic diagnosis would benefit clinical care, prognosis and preventative treatments. Until recently, this diagnosis has usually been performed via Sanger sequencing of a limited number of candidate genes. High-throughput sequencing is revolutionizing the genetic diagnosis of diseases, including bleeding disorders. We have designed a novel high-throughput sequencing platform to investigate the unknown molecular pathology in a cohort of 82 patients with inherited platelet disorders. Thirty-four (41.5%) patients presented with a phenotype strongly indicative of a particular type of platelet disorder. The other patients had clinical bleeding indicative of platelet dysfunction, but with no identifiable features. The high-throughput sequencing test enabled a molecular diagnosis in 70% of these patients. This sensitivity increased to 90% among patients suspected of having a defined platelet disorder. We found 57 different candidate variants in 28 genes, of which 70% had not previously been described. Following consensus guidelines, we qualified 68.4% and 26.3% of the candidate variants as being pathogenic and likely pathogenic, respectively. In addition to establishing definitive diagnoses of well-known inherited platelet disorders, high-throughput sequencing also identified rarer disorders such as sitosterolemia, filamin and actinin deficiencies, and G protein-coupled receptor defects. This included disease-causing variants in DIAPH1 (n=2) and RASGRP2 (n=3). Our study reinforces the feasibility of introducing high-throughput sequencing technology into the mainstream laboratory for the genetic diagnostic practice in inherited platelet disorders.

Comparison of multiple electrode aggregometry with lumi-aggregometry for the diagnosis of patients with mild bleeding disorders

Essentials There is a clinical need for new technologies to measure platelet function in whole blood. Mild bleeding disorders were evaluated using multiple electrode aggregometry (MEA). MEA is insensitive at detecting patients with mild platelet function and secretion defects. More studies are required to investigate MEA in patients with a defined set of platelet disorders.

SUMMARY

Background Multiple electrode aggregometry (MEA) measures changes in electrical impedance caused by platelet aggregation in whole blood. This approach is faster, more convenient and offers the advantage over light transmission aggregometry (LTA) of assessing platelet function in whole blood and reducing preanalytical errors associated with preparation of platelet-rich plasma (PRP). Several studies indicate the utility of this method in assessing platelet inhibition in individuals taking antiplatelet agents (e.g. aspirin and clopidogrel). Objective Our current study sought to evaluate the ability of MEA in diagnosing patients with mild bleeding disorders by comparison with light transmission lumi-aggregometry (lumi-LTA). Methods Forty healthy subjects and 109 patients with a clinical diagnosis of a mild bleeding disorder were recruited into the UK Genotyping and Phenotyping of Platelets study (GAPP, ISRCTN 77951167). MEA was performed on whole blood using one or two concentrations of ADP, PAR-1 peptide, arachidonic acid and collagen. Lumi-LTA was performed in PRP using several concentrations of ADP, adrenaline, arachidonic acid, collagen, PAR-1 peptide and ristocetin. Results Of 109 patients tested, 54 (49%) patients gave abnormal responses by lumi-LTA to one or more agonists. In contrast, only 16 (15%) patients were shown to have abnormal responses to one or more agonists by MEA. Conclusions In this study we showed that MEA is less sensitive in identifying patients with abnormal platelet function relative to lumi-LTA.

Flow cytometry-based platelet function testing is predictive of symptom burden in a cohort of bleeders

Platelet function disorders (PFDs) are common in patients with mild bleeding disorders (MBDs), yet the significance of laboratory findings suggestive of a PFD remain unclear due to the lack of evidence for a clinical correlation between the test results and the patient phenotype. Herein, we present the results from a study evaluating the potential utility of platelet function testing using whole-blood flow cytometry in a cohort of 105 patients undergoing investigation for MBD. Subjects were evaluated with a test panel comprising two different activation markers (fibrinogen binding and P-selectin exposure) and four physiologically relevant platelet agonists (ADP, PAR1-AP, PAR4-AP, and CRP-XL). Abnormal test results were identified by comparison with reference ranges constructed from 24 healthy controls or with the fifth percentile of the entire patient cohort. We found that the abnormal test results are predictive of bleeding symptom severity, and that the greatest predictive strength was achieved using a subset of the panel, comparing measurements of fibrinogen binding after activation with all four agonists with the fifth percentile of the patient cohort (p = 0.00008, hazard ratio 8.7; 95% CI 2.5-40). Our results suggest that whole-blood flow cytometry-based platelet function testing could become a feasible alternative for the investigation of MBDs. We also show that platelet function testing using whole-blood flow cytometry could provide a clinically relevant quantitative assessment of platelet-related hemostasis.