Platelet disorders in children: A diagnostic approach

Gaining Insights into Inherited Bleeding Disorders of Complex Etiology in Pediatric Patients: Whole-Exome Sequencing as First-Line Investigation Tool

INTRODUCTION

 Investigation of the molecular basis of inherited bleeding disorders (IBD) is mostly performed with gene panel sequencing. However, the continuous discovery of new related genes underlies the limitation of this approach. This study aimed to identify genetic variants responsible for IBD in pediatric patients using whole-exome sequencing (WES), and to provide a detailed description and reclassification of candidate variants.

MATERIAL AND METHODS

 WES was performed for 18 pediatric patients, and variants were filtered using a first-line list of 290 genes. Variant prioritization was discussed in a multidisciplinary team based on genotype-phenotype correlation, and segregation studies were performed with available family members.

RESULTS

 The study identified 22 candidate variants in 17 out of 18 patients (94%). Eleven patients had complete genotype-phenotype correlation, resulting in a diagnostic yield of 61%, 5 (28%) were classified as partially solved, and 2 (11%) remained unsolved. Variants were identified in platelet (ACTN1, ANKRD26, CYCS, GATA1, GFI1B, ITGA2, NBEAL2, RUNX1, SRC, TUBB1), bleeding (APOLD1), and coagulation (F7, F8, F11, VWF) genes. Notably, 9 out of 22 (41%) variants were previously unreported. Variant pathogenicity was assessed according to the American College of Medical Genetics and Genomics guidelines and reclassification of three variants based on family segregation evidence, resulting in the identification of 10 pathogenic or likely pathogenic variants, 6 variants of uncertain significance, and 6 benign or likely benign variants.

CONCLUSION

 This study demonstrated the high potential of WES in identifying rare molecular defects causing IBD in pediatric patients, improving their management, prognosis, and treatment, particularly for patients at risk of malignancy and/or bleeding due to invasive procedures.

ISTH bleeding assessment tool and platelet function analyzer in children with mild inherited platelet function disorders

OBJECTIVES

To evaluate the diagnostic performance of platelet function analyzer (PFA) and The International Society on Thrombosis and Hemostasis bleeding-assessment-tool (ISTH-BAT) in detecting mild inherited platelet function disorders (IPFDs) in children with suspected bleeding disorders.

METHODS

Prospective single-center diagnostic study including consecutive patients <18 years with suspected bleeding disorder and performing a standardized workup for platelet function defects including ISTH-BAT, PFA, platelet aggregation testing, blood smear-based immunofluorescence, and next-generation sequencing-based genetic screening for IPFDs.

RESULTS

We studied 97 patients, of which 34 von Willebrand disease (VWD, 22 type-1, 11 type-2), 29 IPFDs (including delta-/alpha-storage pool disease, Glanzmann thrombasthenia, Hermansky-Pudlak syndrome) and 34 with no diagnosis. In a model combining PFA-adenosine diphosphate (ADP), PFA-epinephrine (EPI), and ISTH-BAT overall performance to diagnose IPFDs was low with area under the curves of 0.56 (95% CI 0.44, 0.69) compared with 0.84 (95% CI 0.76, 0.92) for VWD. Correlation of PFA-EPI/-ADP and ISTH-BAT was low with 0.25/0.39 Spearman's correlation coefficients. PFA were significantly prolonged in patients with VWD and Glanzmann thrombasthenia. ISTH-BAT-scores were only positive in severe bleeding disorders, but not in children with mild IPFDs or VWD.

CONCLUSION

Neither ISTH-BAT nor PFA or the combination of both help diagnosing mild IPFDs in children. PFA is suited to exclude severe IPFDs or VWD and is in this regard superior to ISTH-BAT in children.

Egyptian Pediatric Guidelines for the Management of Children with Isolated Thrombocytopenia Using the Adapted ADAPTE Methodology-A Limited-Resource Country Perspective

BACKGROUND

Thrombocytopenia is a prevalent presentation in childhood with a broad spectrum of etiologies, associated findings, and clinical outcomes. Establishing the cause of thrombocytopenia and its proper management have obvious clinical repercussions but may be challenging. This article provides an adaptation of the high-quality Clinical Practice Guidelines (CPGs) of pediatric thrombocytopenia management to suit Egypt's health care context.

METHODS

The Adapted ADAPTE methodology was used to identify the high-quality CPGs published between 2010 and 2020. An expert panel screened, assessed and reviewed the CPGs and formulated the adapted consensus recommendations based on the best available evidence.

DISCUSSION

The final CPG document provides consensus recommendations and implementation tools on the management of isolated thrombocytopenia in children and adolescents in Egypt. There is a scarcity of evidence to support recommendations for various management protocols. In general, complete clinical assessment, full blood count, and expert analysis of the peripheral blood smear are indicated at initial diagnosis to confirm a bleeding disorder, exclude secondary causes of thrombocytopenia and choose the type of work up required. The International Society of Hemostasis and thrombosis-Bleeding assessment tool (ISTH-SCC BAT) could be used for initial screening of bleeding manifestations. The diagnosis of immune thrombocytopenic purpura (ITP) is based principally on the exclusion of other causes of isolated thrombocytopenia. Future research should report the outcome of this adapted guideline and include cost-analysis evaluations.

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.

Medich Giant Platelet Syndrome: An Evolving Qualitative and Quantitative Platelet Disorder

Qualitative platelet disorders remain rare and varied. We describe here 2 additional patients with giant platelets, thrombocytopenia, deficiency in alpha granules and the presence of membranous inclusions within the cytoplasm. Collectively known as Medich syndrome, we further elucidated structural and clinical features of this rare syndrome. Platelets obtained from 2 patients with macro-thrombocytopenia were evaluated by electron microscopy. Structural findings were correlated with clinical characteristics. The defining morphologic feature found in the platelets of these patients is the presence of long, tubular inclusions consisting of several layers of membrane wrapped around a core of cytoplasm. These inclusions may deform the discoid shape of the platelet. In addition, abnormal giant alpha granules are present. Clinically all patients in the current report and review of the literature had mucosal bleeding and were often misdiagnosed as having immune related thrombocytopenia. To date five cases of Medich giant platelet syndrome have been reported. The cases are unified by the ultrastructural findings of abnormal alpha granules and unusual cytoplasmic scrolls. All patients experienced mucosal bleeding, however many clinical, biologic and genetic characteristics of this rare disorder remain to be determined.

Gastrointestinal Bleeding in Congenital Bleeding Disorders

Gastrointestinal bleeding (GIB) is serious, intractable, and potentially life-threatening condition. There is considerable heterogeneity in GIB phenotypes among congenital bleeding disorders (CBDs), making GIB difficult to manage. Although GIB is rarely encountered in CBDs, its severity in some patients makes the need for a comprehensive and precise assessment of underlying factors and management approaches imperative. Initial evaluation of GIB begins with assessment of hematological status; GIB should be ruled out in patients with chronic anemia, and in presentations that include hematemesis, hematochezia, or melena. High-risk patients with recurrent GIB require urgent interventions such as replacement therapy for treatment of coagulation factor deficiency (CFD). However, the best management strategy for CFD-related bleeding remains controversial. While several investigations have identified CBDs as potential risk factors for GIB, research has focused on assessing the risks for individual factor deficiencies and other CBDs. This review highlights recent findings on the prevalence, management strategies, and alternative therapies of GIB related to CFDs, and platelet disorders.

"CHildren with Inherited Platelet disorders Surveillance" (CHIPS) retrospective and prospective observational cohort study by Italian Association of Pediatric Hematology and Oncology (AIEOP)

BACKGROUND

Inherited thrombocytopenias (ITs) are rare congenital bleeding disorders characterized by different clinical expression and variable prognosis. ITs are poorly known by clinicians and often misdiagnosed with most common forms of thrombocytopenia.

MATERIAL AND METHODS

"CHildren with Inherited Platelet disorders Surveillance" study (CHIPS) is a retrospective - prospective observational cohort study conducted between January 2003 and January 2022 in 17 centers affiliated to the Italian Association of Pediatric Hematology and Oncology (AIEOP). The primary objective of this study was to collect clinical and laboratory data on Italian pediatric patients with inherited thrombocytopenias. Secondary objectives were to calculate prevalence of ITs in Italian pediatric population and to assess frequency and genotype-phenotype correlation of different types of mutations in our study cohort.

RESULTS

A total of 139 children, with ITs (82 male - 57 female) were enrolled. ITs prevalence in Italy ranged from 0.7 per 100,000 children during 2010 to 2 per 100,000 children during 2022. The median time between the onset of thrombocytopenia and the diagnosis of ITs was 1 years (range 0 - 18 years). A family history of thrombocytopenia has been reported in 90 patients (65%). Among 139 children with ITs, in 73 (53%) children almost one defective gene has been identified. In 61 patients a pathogenic mutation has been identified. Among them, 2 patients also carry a variant of uncertain significance (VUS), and 4 others harbour 2 VUS variants. VUS variants were identified in further 8 patients (6%), 4 of which carry more than one variant VUS. Three patients (2%) had a likely pathogenic variant while in 1 patient (1%) a variant was identified that was initially given an uncertain significance but was later classified as benign. In addition, in 17 patients the genetic diagnosis is not available, but their family history and clinical/laboratory features strongly suggest the presence of a specific genetic cause. In 49 children (35%) no genetic defect were identified. In ninetyseven patients (70%), thrombocytopenia was not associated with other clinically apparent disorders. However, 42 children (30%) had one or more additional clinical alterations.

CONCLUSION

Our study provides a descriptive collection of ITs in the pediatric Italian population.

Platelet Disorders

After vascular injury and exposure of subendothelial matrix proteins to the intravascular space, mediators of hemostasis are triggered and allow for clot formation and restoration of vascular integrity. Platelets are the mediators of primary hemostasis, creating a platelet plug and allowing for initial cessation of bleeding. Platelet disorders, qualitative and quantitative, may result in bleeding signs and symptoms, particularly mucocutaneous bleeding such as epistaxis, bruising, petechiae, and heavy menstrual bleeding. Increasing evidence suggests that platelets have functional capabilities beyond hemostasis, but this review focuses solely on platelet hemostatic properties. Herein, normal platelet function as well as the effects of abnormal function and thrombocytopenia are reviewed.

Flow cytometric mepacrine fluorescence can be used for the exclusion of platelet dense granule deficiency

BACKGROUND

δ-storage pool disease (δ-SPD) is a bleeding disorder characterized by a reduced number of platelet-dense granules. The diagnosis of δ-SPD depends on the measurement of platelet ADP content, but this test is time consuming and requires a relatively large blood volume. Flow cytometric analysis of platelet mepacrine uptake is a potential alternative, but this approach lacks validation, which precludes its use in a diagnostic setting.

OBJECTIVES

To evaluate the performance of platelet mepacrine uptake as a diagnostic test for δ-SPD.

PATIENTS/METHODS

Mepacrine fluorescence was determined with flow cytometry before and after platelet activation in 156 patients with a suspected platelet function disorder and compared with platelet ADP content as a reference test. Performance was analyzed with a receiver operating characteristic (ROC) curve.

RESULTS

Eleven of 156 patients had δ-SPD based on platelet ADP content. Mepacrine fluorescence was inferior to platelet ADP content in identifying patients with δ-SPD, but both mepacrine uptake (area under the ROC curve [AUC] 0.87) and mepacrine release after platelet activation (AUC 0.80) had good discriminative ability. In our tertiary reference center, mepacrine uptake showed high negative predicitive value (97%) with low positive predictive value (35%). Combined with a negative likelihood ratio of 0.1, these data indicate that mepacrine uptake can be used to exclude δ-SPD in patients with a bleeding tendency.

CONCLUSION

Mepacrine fluorescence can be used as a screening tool to exclude δ-SPD in a large number of patients with a suspected platelet function disorder.

Identification of three novel pathogenic ITGA2B and one novel pathogenic ITGB3 mutations in patients with hereditary Glanzmann's thrombasthenia living in Eastern Turkey

Glanzmann's thrombasthenia (GT) is an autosomal recessive disorder in which the underlying problem is the lack or dysfunction of the GpIIb/IIIa receptor on the platelet surface. The present study determines the genetic mutation typology and analyzes the association between mutation types and clinical findings in patients diagnosed with GT who were followed up in Department of Pediatric Hematology of the Yüzüncü Yıl University School of Medicine. The medical charts of 17 patients who underwent therapy and that were followed up in the Department of Pediatric Hematology of the Yüzüncü Yıl University Dursun Odabaş Medical Center between January 2008 and April 2018 were reviewed retrospectively. Data on such patient characteristics as present genetic mutations, age, gender, age at diagnosis, presenting symptoms, clinical findings, and platelet count and volume were garnered from the patient records. Of the 12 patients identified with genetic mutations, six had the same type of mutation, while four were identified with novel mutations that have to date not been defined in literature. Of these four mutations, three were located in the ITGA2B gene and one in the ITGB3 gene. The present study identified no significant association between the genetic and clinical findings of the patients. Novel mutations were identified in four cases in the present study. No association was found between the mutation type, and the bleeding scores and bleeding phenotypes of the patients. Further studies involving a larger number of patients are required to determine the relationship between the genotypes and clinical findings in patients with GT.

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.

Outcomes in Mild to Moderate Isolated Thrombocytopenia

OBJECTIVES

Incidental isolated mild to moderate thrombocytopenia is a frequent laboratory finding prompting a referral to pediatric hematology-oncology. We tested the hypothesis that patients with isolated asymptomatic mild thrombocytopenia would not progress to require an intervention from a pediatric hematologist-oncologist.

METHODS

This is a 5-year retrospective review of 113 patients referred to pediatric hematology-oncology for isolated thrombocytopenia. Initial, lowest, and current platelet counts along with clinical course and need for interventions were recorded. Thrombocytopenia was categorized as mild (platelet count: 101-140 × 10³/μL), moderate (platelet count: 51-100 × 10³/μL), severe (platelet count: 21-50 × 10³/μL), and very severe (platelet count: ≤20 × 10³/μL).

RESULTS

Eight of 48 patients (17%) referred for initial mild isolated thrombocytopenia progressed to moderate thrombocytopenia at 1 visit. At present, 2 of these patients have moderate thrombocytopenia, 17 remain with mild thrombocytopenia, and 29 patients have resolved thrombocytopenia. Nine of 65 patients (14%) referred for moderate thrombocytopenia progressed to severe or very severe thrombocytopenia on 1 occasion. At present, no patients have severe thrombocytopenia, 18 remain with moderate thrombocytopenia, 14 improved to mild thrombocytopenia, and 33 have resolved thrombocytopenia. Only 3 patients required interventions from a hematologist, whereas 10 patients required therapy from other subspecialties.

CONCLUSIONS

We only identified 3 patients (3%) with mild to moderate thrombocytopenia who required an intervention from a hematologist to improve platelet counts. Patients with isolated mild thrombocytopenia with a normal bleeding history and physical examination findings frequently have normalized their platelet counts within 1 month.

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.

Diagnose angeborener Störungen der Thrombozytenfunktion

Angeborene Störungen der Thrombozytenfunktion sind eine heterogene Gruppe von Erkrankungen, die oft erst bei Auftreten von Blutungen erkannt werden. Im klinischen Bereich haben sich nur wenige Methoden zur Diagnose und Klassifizierung von angeborenen Thrombozytenfunktionsstörungen bewährt. Für eine rationelle Diagnostik ist ein stufenweises Vorgehen empfehlenswert. Anamnese und klinische Untersuchung sind Grundvoraussetzungen. Das von-Willebrand-Syndrom und andere plasmatische Gerinnungsstörungen sollten vor einer spezifischen Thrombozytenfunktionsdiagnostik immer ausgeschlossen werden. Die Bestimmung von Zahl, Größe, Volumen (MPV) und Morphologie der Thrombozyten erlauben Rückschlüsse auf die zu Grunde liegende Störung.

Die PFA-100®-Verschlusszeit eignet sich als Screening zum Ausschluss schwerer Thrombozytenfunktionsstörungen. Die Aggrego metrie ermöglicht die Untersuchung zahlreicher Aspekte der Thrombozytenfunktion. Die Durchflusszytometrie ist zur Diagnose von Thrombasthenie Glanzmann, Bernard-Soulier- Syndrom und Freisetzungsstörungen geeignet. Molekulargenetische Untersuchungen können die Verdachtsdiagnose bestätigen oder zum Nachweis nicht beschriebener Defekte verwendet werden. Hier wird die ungekürzte Version der inter -disziplinären Leitlinie* präsentiert.

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.

Evaluating platelet function disorders in children with bleeding tendency - A single center study

Platelet function disorders (PFDs) are a common cause of mild bleeding tendency. However, they cannot be recognized by standard screening studies. The gold standard test for PFD is platelet aggregation, performed by light transmission aggregometry (LTA). A newer and less validated method is the closure time (CT), performed by the platelet function Analyzer 100 (PFA-100). Data regarding the validity of these tests in children are limited. The aim of this study was to evaluate the usefulness of LTA and PFA-100 for the diagnosis of pediatric patients with bleeding tendency. This retrospective study included patients one month-18 year old that had LTA tests performed at the coagulation laboratory of Rabin Medical Center between the years 2006-2015. Bleeding severity was assessed using a pediatric bleeding score. Patients were excluded from analysis if they had thrombocytopenia, thrombocytosis or coagulation factors deficiencies. One hundred and thirty-seven (137) patients were included in the analysis. The median age was 7.5 years (range one month-18 years). Most patients (93%) had a bleeding score of 2 or more. Abnormal LTA was found in 40% and prolonged CT in 23% of the patients. Abnormal LTA was significantly more common in patients with a bleeding score of 2 or more compared to patients with a lower bleeding scores (P = 0.04). No significant correlation was found between the bleeding severity and the number of agonists which induced abnormal responses (p = 0.52) or the CT (p = 0.35). Furthermore, no correlation was found between abnormal LTA and prolonged CT. To conclude, we were able to diagnose 40% of children who presented with bleeding tendency with platelet aggregation defects by LTA. Abnormal LTA was significantly more prevalent in patients with a bleeding score of 2 and above. In contrast, CT was not found to be sensitive as a screening tool for PFD. Therefore, our data extend the validity of the use of LTA for the evaluation of pediatric patients with bleeding tendency.

Light Transmission Aggregometry Does Not Correlate With the Severity of δ-Granule Platelet Storage Pool Deficiency

Delta-granule platelet storage pool deficiency (δ-PSPD) is a poorly studied bleeding diathesis resulting from either decreased granule content or decreased average number of platelet δ-granules. Light transmission aggregometry (LTA) is commonly used to evaluate for δ-PSPD and platelet electron microscopy (EM) is used to confirm the diagnosis. Currently, little data exist examining the relationship between the likelihood of abnormal platelet aggregation findings, severity of δ-granule deficiency on platelet EM, and severity of bleeding symptoms in patients with δ-PSPD. Patients diagnosed with δ-PSPD by platelet EM who also underwent LTA testing were identified at a single institution for correlation between severity of bleeding, average number of platelet δ-granules, and number of agonist abnormalities on LTA. No statistically significant association was identified between the average number of δ-granules per platelet and likelihood of an abnormal LTA. LTA abnormalities were quite varied and only 50% diagnosed with δ-PSPD on EM had abnormal aggregation testing. Also, no correlation was seen between the number of clinical bleeding symptoms, number of average δ-granules per platelet, and the number of LTA agonist abnormalities. Our findings highlight the difficulties inherent in the laboratory evaluation of platelet function.

Inherited platelet function disorders. Diagnostic approach and management

Inherited platelet function disorders (IPFDs) make up a significant proportion of congenital bleeding diatheses, but they remain poorly understood and often difficult to diagnose. Therefore, a rational diagnostic approach, based on a standardized sequence of laboratory tests, with consecutive steps of increasing level of complexity, plays a crucial role in the diagnosis of most IPFDs. In this review we discuss a diagnostic approach through platelet phenotyping and genotyping and we give an overview of the options for the management of bleeding in these disorders and an account of the few systematic studies on the bleeding risk associated with invasive procedures and its treatment.

Laboratory testing for platelet function disorders

Platelet function testing is both complex and labor intensive. A stepwise approach to the evaluation of patients with suspected platelet disorders will optimize the use of laboratory resources, beginning with an appropriate clinical evaluation to determine whether the bleeding is consistent with a defect of primary hemostasis. Bleeding assessment tools, evaluation of platelet counts, and review of peripheral blood cell morphology can aid the initial assessment. For patients requiring further laboratory testing, platelet aggregometry, secretion assays, and von Willebrand factor assays are the most useful next steps and will direct further specialized testing including flow cytometry, electron microscopy, and molecular diagnostics. Guidelines and recommendations for standardizing platelet function testing, with a particular focus on light transmission aggregometry, are available and can provide a template for clinical laboratories in establishing procedures that will optimize diagnosis and assure quality results. This review outlines an approach to platelet function testing and reviews testing methods available to clinical laboratories.

Current status and future prospects for platelet function testing in the diagnosis of inherited bleeding disorders

Platelets play a crucial role in haemostasis by preventing bleeding at the site of vascular injury. Several defects in platelet morphology and function have been identified and described over the years. Although a range of methodologies is available to assess platelet function, a significant proportion of subjects with bleeding symptoms and normal coagulation parameters still appear to have normal results on platelet function testing. This might suggest that the reason for bleeding is multifactorial and is due to a combination of several minor defects in platelet function and/or other parts of the haemostatic system or might indicate that the currently available platelet function tests do not provide optimal diagnostic power. This review will summarize the established platelet function tests used for diagnosing inherited platelet abnormalities in adults and children, and discuss the newly developed methodologies as well as unmet challenges and potential areas for further improvement in this field.

von Willebrand disease and platelet disorders

The diagnosis and management of bleeding disorders is made difficult by the complexity and variety of disorders, clinical symptoms and bleeding type and severity. von Willebrand disease (VWD) and platelet disorders are disorders of primary haemostasis and together represent the most common inherited bleeding disorders. In this article, we describe the diagnosis of VWD and platelet disorders and the treatment options for VWD.

Neonatal platelets: mediators of primary hemostasis in the developing hemostatic system

The human hemostatic system is developmentally regulated, resulting in qualitative and quantitative differences in the mediators of primary and secondary hemostasis as well as fibrinolysis in neonates and infants. Although gestational age-related differences in coagulation factor levels occur, the existence of a unique neonatal platelet phenotype remains controversial. Complicated by difficulties in obtaining adequate neonatal blood volumes with which to perform functional assays, ambiguity surrounds the characterization of neonatal platelets. Thus, much of the current knowledge of neonatal platelet function has been based on studies from cord blood samples. Studies suggest that cord blood-derived platelets, as a surrogate for neonatal platelets, are hypofunctional when compared with adult platelets. This relative platelet dysfunction, combined with a propensity toward thrombocytopenia in the neonatal intensive care unit population, creates a clinical conundrum regarding the appropriate administration of platelet transfusions. This review provides an appraisal of the distinct functional phenotype of neonatal platelets. Neonatal platelet transfusion practices and the impact of the relatively hypofunctional neonatal platelet on those practices will be considered.

Inherited disorders of platelet function

Inherited platelet function disorders are of variable severity and unknown frequency and may be difficult to diagnose. Nevertheless, they are increasingly recognized as an important cause of bleeding in pediatrics, particularly in adolescent girls with menorrhagia, where they may be more common than von Willebrand disease. This article reviews the presentation of these disorders, summarizes the most common types of platelet function disorders, discusses the challenges in diagnostic testing, and details treatment and supportive care options.

Inherited abnormalities of coagulation: hemophilia, von Willebrand disease, and beyond

Bleeding disorders are broadly classified into primary and secondary hemostatic defects. Primary hemostatic disorders (disorders of platelets and von Willebrand factor) mainly result in mucocutaneous bleeding symptoms such as epistaxis, menorrhagia, petechiae, easy bruising, and bleeding after dental and surgical interventions. Secondary hemostatic disorders (congenital or acquired deficiencies of coagulation factors) typically manifest with delayed, deep bleeding into muscles and joints. This article provides a generalized overview of the pathophysiology, clinical manifestations, laboratory abnormalities, and molecular basis of inherited abnormalities of coagulation with a focus on hemophilia, von Willebrand disease, and rare inherited coagulation disorders.

Rare bleeding disorders in children: identification and primary care management

Bleeding symptoms are common in healthy children but occasionally may indicate an underlying congenital or acquired bleeding diathesis. The rare bleeding disorders (RBDs) comprise inherited deficiencies of coagulation factors I (congenital fibrinogen deficiencies), II, V, VII, X, XI, and XIII and combined factor deficiencies, most notably of factors V and VIII and of vitamin K-dependent factors. These disorders often manifest during childhood and may present with recurrent or even serious or life-threatening bleeding episodes, particularly during the neonatal period. Accordingly, primary care and other nonhematologist pediatric providers should be familiar with the clinical presentation and initial evaluation of these rare disorders. Bleeding manifestations generally vary within the same RBD and may be indistinguishable from 1 RBD to another or from other more common bleeding disorders. Serious bleeding events such as intracranial hemorrhage may be heralded by less serious bleeding symptoms. The results of initial coagulation studies, especially prothrombin time and activated partial thromboplastin time, are often helpful in narrowing down the potential factor deficiency, with factor XIII deficiency being an exception. Consultation with a hematologist is advised to facilitate accurate diagnosis and to ensure proper management and follow-up. The approach to bleeding episodes and invasive procedures is individualized and depends on the severity, frequency, and, in the case of procedures, likelihood of bleeding. Prophylaxis may be appropriate in children with recurrent serious bleeding and specifically after life-threatening bleeding episodes. When available, specific purified plasma-derived or recombinant factor concentrates, rather than fresh frozen plasma or cryoprecipitate, are the treatment of choice.

Brodde M. State of the art in platelet function testing

Platelets perform many functions in hemostasis but also in other areas of physiology and pathology. Therefore, it is obvious that many different function tests have been developed, each one conceived and standardized for a special purpose. This review will summarize the different fields in which platelet function testing is currently in use; diagnostics of patients with bleeding disorders, monitoring patients' response to anti-platelet therapy, monitoring in transfusion medicine (blood donors, platelet concentrates, and after transfusion), and monitoring in perioperative medicine to predict bleeding tendency. The second part of the review outlines different methods for platelet function testing, spanning bleeding time, and platelet counting as well as determining platelet adhesion, platelet secretion, platelet aggregation, platelet morphology, platelet signal transduction, platelet procoagulant activity, platelet apoptosis, platelet proteomics, and molecular biology.

What we have learned from inherited platelet disorders

Identifying the molecular basis of inherited platelet disorders has contributed to our understanding of normal platelet physiology. Many of these conditions are rare, but close observation of clinical and laboratory phenotype, and subsequent identification of the abnormal protein and mutated gene, have provided us with unique opportunities to examine specific aspects of platelet biogenesis and function. Phenotype-genotype association studies are providing a detailed understanding of the structure and function of platelet membrane receptors, the biogenesis and release of platelet granules, and the assembly of the cytoskeleton. Genetic polymorphisms contributing to decreased or increased platelet adhesion and activation may translate into increased clinical risks for bleeding or thrombosis. More recently, genome wide association studies have identified new genes contributing to the variation in normal platelet function.

The use of DDAVP in children with bleeding disorders

Desmopressin (1-deamino-8-D-arginine vasopressin, DDAVP) has been used in children with von Willebrand disease (VWD) and Hemophilia A for almost 35 years. This treatment has substantially lowered the number of children exposed to human plasma derived products, with a good safety profile, and at very low cost. The response to DDAVP has been shown to be associated with age, baseline factor level, and genetic mutations. A DDAVP challenge test is recommended. DDAVP has also been used to prevent and treat bleeding episodes in children with platelet function defects and other disorders associated with bleeding tendency.

Inherited platelet disorders

Inherited diseases of the megakaryocyte lineage give rise to bleeding when platelets fail to fulfill their hemostatic function upon vessel injury. Platelet defects extend from the absence or malfunctioning of adhesion (GPIb-IX-V, Bernard-Soulier syndrome) or aggregation receptors (integrin αIIbβ3, Glanzmann thrombasthenia) to defects of primary receptors for soluble agonists, secretion from storage organelles, activation pathways and the generation of procoagulant activity. In disorders such as the Chediak-Higashi, Hermansky-Pudlak, Wiskott-Aldrich and Scott syndromes the molecular lesion extends to other cells. In familial thrombocytopenia (FT), platelets are produced in insufficient numbers to assure hemostasis. Some FT affect platelet morphology and give rise to the 'giant platelet' syndromes (e.g. MYH9-related diseases) with changes in megakaryocyte maturation within the bone marrow and premature release of platelets. Diseases of platelet production may also affect other cells and in some cases interfere with development and/or functioning of major organs. Diagnosis of platelet disorders requires platelet function testing, studies often aided by the quantitative analysis of receptors by flow cytometry and fluorescence and electron microscopy. New generation DNA-based procedures including whole exome sequencing offer an exciting new perspective. Transfusion of platelets remains the most common treatment of severe bleeding, management with desmopressin is often used for mild disorders. Substitute therapies are available including rFVIIa and the potential use of thrombopoietin analogues for FT. Stem cell or bone marrow transplantation has been successful for several diseases while gene therapy shows promise in the Wiskott-Aldrich syndrome.

An update on pediatric bleeding disorders: bleeding scores, benign joint hypermobility, and platelet function testing in the evaluation of the child with bleeding symptoms

Evaluating a child with symptoms of easy bruising and/or bleeding remains a challenge in pediatric hematology, and there is no "one size fits all" approach. This review focuses on recent research in three elements of the evaluation of a child with a suspected bleeding disorder. We will first discuss the development of the standardized Pediatric Bleeding Questionnaire, and its applications in research and clinical settings. We will then discuss the relationship between benign hypermobility syndromes and hemostasis, and the importance of including a Beighton Score in the physical examination of any child presenting with unusual bruising or bleeding. While prolonged bleeding times and abnormal platelet aggregation are common findings in children with benign hypermobility, normal coagulation studies do not exclude the presence of a connective tissue disorder in a child presenting with easy bleeding and joint hypermobility on examination. Finally, we will discuss the current state of knowledge regarding the laboratory evaluation of platelet function in children. Platelet function disorders are among the most common inherited bleeding disorders. However, testing for such disorders is time-consuming and requires a step-wise approach. We will review the indications for and limitations of the most commonly utilized platelet function laboratory studies.

The bleeding child. Part I: primary hemostatic disorders

Mucocutaneous bleeding is common in childhood and may be the result of primary hemostatic disorders such as vascular abnormalities, von Willebrand disease, thrombocytopenia, and platelet dysfunction. A detailed bleeding history and physical examination are essential to distinguish between normal and abnormal bleeding and to decide whether it is necessary to perform further laboratory evaluation. Initial laboratory tests include complete blood count, peripheral blood smear, mean platelet volume, von Willebrand factor (VWF) antigen assay, VWF ristocetin cofactor activity, and factor VIII activity. Once thrombocytopenia and von Willebrand disease have been excluded, platelet function should be tested by platelet aggregation. Additional specific diagnostic tests, such as platelet secretion tests and flow cytometry for the detection of platelet surface glycoprotein expression, are needed to confirm the raised hypothesis.

What To Do When You Suspect an Inherited Platelet Disorder

Inherited platelet disorders (IPDs) comprise a heterogenous group of diseases that include defects in platelet function and disordered megakaryopoiesis. Some IPDs overlap as both defects in function and thrombopoiesis, resulting in both altered aggregation and/or secretion and thrombocytopenia. This review examines the key features of the presentation of IPDs in children and adults and presents a diagnostic algorithm for the evaluation of these patients. In addition, recent advances in our understanding of the pathophysiology of platelet disorders are addressed, with attention given to some of the novel genetic associations. Finally, treatment options and future therapies are briefly discussed.

How I manage neonatal thrombocytopenia

Although neonatal thrombocytopenia (platelet count < 150×10(9) /l) is a common finding in hospital practice, a careful clinical history and examination of the blood film is often sufficient to establish the diagnosis and guide management without the need for further investigations. In preterm neonates, early-onset thrombocytopenia (<72h) is usually secondary to antenatal causes, has a characteristic pattern and resolves without complications or the need for treatment. By contrast, late-onset thrombocytopenia in preterm neonates (>72h) is nearly always due to post-natally acquired bacterial infection and/or necrotizing enterocolitis, which rapidly leads to severe thrombocytopenia (platelet count<50×10(9) /l). Thrombocytopenia is much less common in term neonates and the most important cause is neonatal alloimmune thrombocytopenia (NAIT), which confers a high risk of perinatal intracranial haemorrhage and long-term neurological disability. Prompt diagnosis and transfusion of human platelet antigen-compatible platelets is key to the successful management of NAIT. Recent studies suggest that more than half of neonates with severe thrombocytopenia receive platelet transfusion(s) based on consensus national or local guidelines despite little evidence of benefit. The most pressing problem in management of neonatal thrombocytopenia is identification of safe, effective platelet transfusion therapy and controlled trials are urgently needed.