Management of the thrombotic risk associated with COVID-19: guidance for the hemostasis laboratory.

Coronavirus disease 2019 (COVID-19) is associated with extreme inflammatory response, disordered hemostasis and high thrombotic risk. A high incidence of thromboembolic events has been reported despite thromboprophylaxis, raising the question of a more effective anticoagulation. First-line hemostasis tests such as activated partial thromboplastin time, prothrombin time, fibrinogen and D-dimers are proposed for assessing thrombotic risk and monitoring hemostasis, but are vulnerable to many drawbacks affecting their reliability and clinical relevance. Specialized hemostasis-related tests (soluble fibrin complexes, tests assessing fibrinolytic capacity, viscoelastic tests, thrombin generation) may have an interest to assess the thrombotic risk associated with COVID-19. Another challenge for the hemostasis laboratory is the monitoring of heparin treatment, especially unfractionated heparin in the setting of an extreme inflammatory response. This review aimed at evaluating the role of hemostasis tests in the management of COVID-19 and discussing their main limitations.

[Risk factors for thromboembolic disease in young women-the role of hormones]. / Facteurs de risque de maladie veineuse thromboembolique chez les jeunes femmes en contexte hormonal: Risque de survenue d'une maladie thromboembolique veineuse chez les membres de la famille au 1er degré de femmes ayant une maladie veineuse thromboembolique en contexte hormonal : étude « FIT ­ H ¼.

Hormonal exposure in young women increases the risk of venous thromboembolic disease (VTE). Thrombophilia testing is often proposed in women of childbearing age before the initiation of contraception. However, the presence of a familial history of VTE has the potential to be more accurate than the presence of inherited thrombophilia. OBJECTIVE: To demonstrate an association between the risk of VTE in young women with hormonal exposure (pregnancy or oral contraceptive use) and the presence of a previous episode of VTE in their first-degree relatives, according to whether or not a detectable inherited thrombophilia was present. METHODS: We will perform a multicenter case-control cross-sectional study. The main risk factor is defined by the presence of a symptomatic VTE in young women with hormonal exposure. The principle variable is the presence of an objectively diagnosed episode of VTE in first-degree relatives. We will need to include 2,200 family members in 440 cases. EXPECTED RESULTS: We expect to improve understanding of the thrombotic risk in first-degree relatives of patients in hormonal context with or without a past history of VTE.

Management of antiplatelet therapy for non elective invasive procedures of bleeding complications: proposals from the French working group on perioperative haemostasis (GIHP), in collaboration with the French Society of Anaesthesia and Intensive Care Medicine (SFAR).

The French Working Group on Perioperative Haemostasis (GIHP) and the French Study Group on Haemostasis and Thrombosis (GFHT) in collaboration with the French Society of Anaesthesia and Intensive Care Medicine (SFAR) drafted up-to-date proposals on the management of antiplatelet therapy for non-elective invasive procedures or bleeding complications. The proposals were discussed and validated by a vote; all proposals could be assigned with a high strength. Emergency management of oral antiplatelet agents (APA) requires knowledge on their pharmacokinetic/pharmacodynamics parameters, evaluation of the degree of the alteration of haemostatic competence and the associated bleeding risk. Platelet function testing may be considered. When APA-induced bleeding risk may worsen the prognosis, measures should be taken to neutralise antiplatelet therapy by considering not only the efficacy of available means (which can be limited for prasugrel and even more for ticagrelor) but also the risks that these means expose the patient to. The measures include platelet transfusion at the appropriate dose and haemostatic agents (tranexamic acid; rFVIIa for ticagrelor). When possible, postponing non-elective invasive procedures at least for a few hours until the elimination of the active compound (which could compromise the effect of transfused platelets) or if possible a few days (reduction of the effect of APA) should be considered.

Intravenous thrombolysis for acute ischaemic stroke in patients on direct oral anticoagulants.

BACKGROUND AND PURPOSE: Whereas intravenous thrombolysis (IVT) is allowed for acute ischaemic stroke in patients on vitamin K antagonists with international normalized ratio ≤1.7, there are no similar recommendations for patients on direct oral anticoagulants (DOACs), notably due to the lack of coagulation tests to assess the therapeutic effects. Although the literature is scarce, consisting of small case series and retrospective studies, considering the frequency of this situation the French Vascular Neurology Society and the French Study Group on Haemostasis and Thrombosis have worked on a joint position paper to provide a practical position regarding the emergency management of ischaemic stroke in patients on DOACs. METHOD: Based on a review of the literature, the authors wrote a first text that was submitted to a broad panel of members from the two societies. The text was then amended by the authors to address experts' comments and to reach a consensus. RESULTS: In patients with normal renal function and who stopped the DOAC for at least 48 h, the management should not differ from that in patients without oral anticoagulant. In patients who are still on DOACs, mechanical thrombectomy is encouraged preferentially when applicable in first line. Otherwise, when specific tests are available, values <50 ng/ml indicate that IVT is allowed. In the absence of specific tests, standard tests (thrombin time, prothrombin time and activated partial thromboplastin time) can be used for dabigatran and rivaroxaban, although interpretation of these tests may be less reliable. In some patients on dabigatran, idarucizumab may be used before IVT. CONCLUSIONS: In this expert opinion paper, it is suggested that IVT can be performed in patients selected according to the time elapsed since the drug was last taken, renal function, type of hospital where the patient is admitted and plasma concentration of DOAC.

Immunogenicity, efficacy and safety of Nuwiq® (human-cl rhFVIII) in previously untreated patients with severe haemophilia A-Interim results from the NuProtect Study.

INTRODUCTION: Nuwiq® (Human-cl rhFVIII) is a fourth generation recombinant FVIII, produced in a human cell line, without chemical modification or protein fusion. No inhibitors developed in studies with Nuwiq® in 201 previously treated patients with haemophilia A (HA). The immunogenicity, efficacy and safety of Nuwiq® in previously untreated patients (PUPs) with severe HA are being assessed in the ongoing NuProtect study. METHODS: The study, conducted across 38 centres worldwide, is evaluating 110 true PUPs of all ages and ethnicities enrolled for study up to 100 exposure days (EDs) or 5 years maximum. The primary objective is to assess the immunogenicity of Nuwiq® (inhibitor activity ≥0.6 BU) using the Nijmegen-modified Bethesda assay at a central laboratory. RESULTS: Data for 66 PUPs with ≥20 EDs from a preplanned interim analysis were analysed. High-titre (HT) inhibitors developed in 8 of 66 patients after a median of 11.5 EDs (range 6-24). Five patients developed low-titre inhibitors (4 transient). The cumulative incidence (95% confidence interval) was 12.8% (4.5%, 21.2%) for HT inhibitors and 20.8% (10.7%, 31.0%) for all inhibitors. During inhibitor-free periods, median annualized bleeding rates during prophylaxis were 0 for spontaneous bleeds and 2.40 for all bleeds. Efficacy was rated as "excellent" or "good" in treating 91.8% of bleeds. Efficacy of surgical prophylaxis was "excellent" or "good" for 8 (89%) procedures and "moderate" for 1 (11%). No tolerability concerns were evident. CONCLUSION: These interim data show a cumulative incidence of 12.8% for HT inhibitors and convincing efficacy and tolerability in PUPs treated with Nuwiq® .

Postauthorization safety study of Clottafact® , a triply secured fibrinogen concentrate in acquired fibrinogen deficiency: a prospective observational study.

BACKGROUND AND OBJECTIVES: A postauthorization safety study was performed between 2009 and 2012 to describe the use of Clottafact® in acquired fibrinogen deficiency in real-life medical practice in France. MATERIALS AND METHODS: One hundred and fifty patients were planned for 28 days of prospective follow-up after infusion. The analysis of this observational study was descriptive and performed according to the type of treatment (curative or preventive) and the origin of the bleed. RESULTS: One hundred and fifty-six patients (16-87 years) were included in 13 centres and treated in five different medical bleeding situations: postpartum (59), other gynaecological/obstetrical (6), trauma (34), liver (13), cardiovascular (23) and other various bleeding situations (21). The mean follow-up time was 18·9 ± 12·3 days. Two patients presented adverse drug reactions: one a pulmonary embolism and the other a four-site venous thromboembolic episode. All were serious with a dubious causal relationship with the study treatment. Efficacy data were collected as a secondary objective. In 150 patients receiving curative treatment, 117 of 159 infusions (73·6%) were considered as successful by the investigators, 35 as moderate (22%) and seven as no response (4·4%). CONCLUSION: The Clottafact® safety profile observed during the study matched the known profile of fibrinogen during use.

[Neonatal arterial ischemic stroke: Which thrombotic biological risk factors to investigate and which practical consequences?] / Accident vasculaire cérébral ischémique du nouveau-né : quels facteurs biologiques de risque thrombotique rechercher et quelles conséquences en pratique ?

All biological risk factors that have been previously identified to increase the risk of thrombosis in adults, have also been studied in neonates with arterial Ischemic Stroke (NAIS), but most studies were retrospective and included relatively low numbers of affected children. We therefore could not suggest recommendations with a strong level of evidence and only expert proposals potentially useful for clinical practice will be presented in this text. Despite these limitations, the extensive analysis of published data supported that factor V Leiden (FVL) and increased levels of Lp(a) could be significant risk factors for NAIS. Importantly, these 2 risk factors cannot be considered as having provoked NAIS, and moreover, they do not influence the prognosis and the immediate treatment. However, since the FVL may have an impact for the prescription of a thromboprophylaxis when the neonate will become adult, to look for its presence in affected patients may be justified. For clinical practice, the following propositions can be applied: 1. Routine testing for thrombophilia (AT, PC PS deficiency, FV Leiden or FII20210A) or for detecting other biological risk factors such as antiphospholipid antibodies, high FVIII, homocystein or Lp(a) levels, MTHFR thermolabile variant, should not be considered in neonates with NAIS. 2. Testing for FV Leiden can be performed in case of documented family history of venous thromboembolic disease. 3. Testing neonates for the presence of antiphospholipid antibodies (APA) is mandatory in case of clinical events suggesting antiphospholipid syndrome in the mother (vascular thrombosis, and/or pregnancy morbidity). 4. Routine testing for thrombophilia is not proposed in both parents in case of early death of the neonate, apart from APA in the mother.

5B9, a monoclonal antiplatelet factor 4/heparin IgG with a human Fc fragment that mimics heparin-induced thrombocytopenia antibodies.

Essentials No humanized monoclonal antibody was available to study heparin-induced thrombocytopenia (HIT). We developed the first anti-platelet factor 4 (PF4)/heparin antibody with a human Fc fragment. This antibody (5B9) fully mimics the effects of human HIT antibodies. 5B9 binds two regions within PF4 that may be critical for the pathogenicity of HIT antibodies. SUMMARY: Background The diagnosis of heparin-induced thrombocytopenia (HIT) is based on clinical and biological criteria, but a standard is lacking for laboratory assays. Moreover, no humanized HIT antibody is available for pathophysiological studies. Objective To characterise 5B9, a chimeric monoclonal antibody, which fully mimics the effects of human HIT antibodies. Methods/Results 5B9, a chimeric anti-platelet factor 4/heparin complexes IgG1 antibody, was obtained after immunizing specific transgenic mice. 5B9 induced heparin FcγRIIA-dependent platelet aggregation and tissue factor mRNA synthesis in monocytes. It also induced significant thrombocytopenia and thrombin generation in mice expressing human PF4 and FcγRIIA receptors. The binding of 5B9 to PF4/H complexes was inhibited by 15 of 25 HIT plasma samples and only three of 25 samples containing non-pathogenic anti-PF4/H antibodies. KKO, a murine IgG2b HIT antibody, also inhibited the binding of 5B9 to PF4/H, suggesting that epitopes recognized by both antibodies are close. A docking analysis based on VH and VL sequences of 5B9 showed that binding of 5B9 Fab to PF4 involved 12 and 12 residues in B and D monomers, respectively, including seven previously identified as critical to the formation of a PF4/KKO complex. Two regions (Asp-7 to Thr-15 and Ala-32 to Thr-38) therefore appeared important for the binding of 5B9 and KKO on PF4 modified by heparin. Conclusions 5B9 is the first anti-PF4/H monoclonal antibody with a human Fc fragment, which induces similar cellular activation as HIT antibodies. Moreover, 5B9 binds epitopes within PF4 that are likely to be critical for the pathogenicity of HIT antibodies.

[Neonatal arterial ischemic stroke: Review of the current guidelines]. / Accidents vasculaires cérébraux ischémiques artériels néonatals : synthèse des recommandations.

Neonatal arterial ischemic stroke (NAIS) is a rare event that occurs in approximately one in 5000 term or close-to-term infants. Most affected infants will present with seizures. Although a well-recognized clinical entity, many questions remain regarding diagnosis, risk factors, treatment, and follow-up modalities. In the absence of a known pathophysiological mechanism and lack of evidence-based guidelines, only supportive care is currently provided. To address these issues, a French national committee set up by the French Neonatal Society (Société française de néonatologie) and the national referral center (Centre national de référence) for arterial ischemic stroke in children drew up guidelines based on an HAS (Haute Autorité de santé [HAS]; French national authority for health) methodology. The main findings and recommendations established by the study group are: (1) among the risk factors, male sex, primiparity, caesarean section, perinatal hypoxia, and fetal/neonatal infection (mainly bacterial meningitis) seem to be the most frequent. As for guidelines, the study group recommends the following: (1) the transfer of neonates with suspected NAIS to a neonatal intensive care unit with available equipment to establish a reliable diagnosis with MRI imaging and neurophysiological monitoring, preferably by continuous video EEG; (2) acute treatment of suspected infection or other life-threatening processes should be addressed immediately by the primary medical team. Persistent seizures should be treated with a loading dose of phenobarbital 20mg/kg i.v.; (3) MRI of the brain is considered optimal for the diagnosis of NAIS. Diffusion-weighted imaging with apparent diffusion coefficient is considered the most sensitive measure for identifying infarct in the neonatal brain. The location and extent of the lesions are best assessed between 2 and 4 days after the onset of stroke; (4) routine testing for thrombophilia (AT, PC PS deficiency, FV Leiden or FII20210A) or for detecting other biological risk factors such as antiphospholipid antibodies, high FVIII, homocysteinemia, the Lp(a) test, the MTHFR thermolabile variant should not be considered in neonates with NAIS. Testing for FV Leiden can be performed only in case of a documented family history of venous thromboembolic disease. Testing neonates for the presence of antiphospholipid antibodies should be considered only in case of clinical events arguing in favor of antiphospholipid syndrome in the mother; (5) unlike childhood arterial ischemic stroke, NAIS has a low 5-year recurrence rate (approximately 1 %), except in those children with congenital heart disease or multiple genetic thrombophilia. Therefore, initiation of anticoagulation or antithrombotic agents, including heparin products, is not recommended in the newborn without identifiable risk factors; (6) the study group recommends that in case of delayed motor milestones or early handedness, multidisciplinary rehabilitation is recommended as early as possible. Newborns should have physical therapy evaluation and ongoing outpatient follow-up. Given the risk of later-onset cognitive, language, and behavioral disabilities, neuropsychological testing in preschool and at school age is highly recommended.

Post-authorization safety study of Clottafact® , a triply secured fibrinogen concentrate in congenital afibrinogenemia. A prospective observational study.

BACKGROUND AND OBJECTIVES: A new fibrinogen concentrate Clottafact® was developed according to European guidelines on plasma-derived products. A post-authorization safety study was set up in 2009 as part of the risk management plan. This was a non-interventional, prospective, non-comparative, multicenter study of the use of fibrinogen concentrate for congenital afibrinogenemia in real-life medical practice in France. MATERIALS AND METHODS: The analysis was descriptive and performed on 3 subgroups: prophylaxis vs. on-demand treatment, age (<6, <12 and ≥12) and severity of the deficiency. RESULTS: Fourteen patients [1-78 years] were included in 7 centres and followed for 1 year. Twenty-one adverse drug reactions (ADRs) classically reported with fibrinogen (pallor, chills, cough, vomiting, headache, urticaria and erythematous rash) were reported in 5 of 14 patients. Two ADRs were serious: an anaphylactic shock and a subclavian venous thrombosis with a favourable outcome without sequelae. In the nine patients under prophylaxis, 365 of 367 infusions were considered as successful (99·5%) and 2 as failures. For the five patients treated on-demand, the efficacy was rated as excellent for 27 of 48 infusions and good for the 21 others. CONCLUSION: This study confirms that the benefit/risk balance for this fibrinogen concentrate is favourable.

Anti-A2 and anti-A1 domain antibodies are potential predictors of immune tolerance induction outcome in children with hemophilia A.

BACKGROUND: Hemophilia A (HA) is a congenital bleeding disorder resulting from factor VIII deficiency. The most serious complication of HA management is the appearance of inhibitory antibodies (Abs) against injected FVIII concentrates. To eradicate inhibitors, immune tolerance induction (ITI) is usually attempted, but it fails in up to 30% of cases. Currently, no undisputed predictive marker of ITI outcome is available to facilitate the clinical decision. OBJECTIVES: To identify predictive markers of ITI efficacy. METHODS: The isotypic and epitopic repertoires of inhibitory Abs were analyzed in plasma samples collected before ITI initiation from 15 children with severe HA and high-titer inhibitors, and their levels were compared in the two outcome groups (ITI success [n = 7] and ITI failure [n = 8]). The predictive value of these candidate biomarkers and of the currently used indicators (inhibitor titer and age at ITI initiation, highest inhibitor titer before ITI, and interval between inhibitor diagnosis and ITI initiation) was then compared by statistical analysis (Wilcoxon test and receiver receiver operating characteristic [ROC] curve analysis). RESULTS: Whereas current indicators seemed to fail in discriminating patients in the two outcome groups (ITI success or failure), anti-A1 and anti-A2 Ab levels before ITI initiation appeared to be good potential predictive markers of ITI outcome (P < 0.018). ROC analysis showed that anti-A1 and anti-A2 Abs were the best at discriminating between outcome groups (area under the ROC curve of > 0.875). CONCLUSION: Anti-A1 and anti-A2 Abs could represent new promising tools for the development of ITI outcome prediction tests for children with severe HA.

[Heparin-induced thrombocytopenia: recent data]. / Les thrombocytopénies induites par l'héparine: données récentes.

Despite less frequent, heparin-induced thrombocytopenia (HIT) remains a severe complication of treatment with heparin, and is important to diagnose and manage appropriately. HIT results from an atypical immune response to heparin, with the synthesis of IgG antibodies specific to heparin-modified platelet factor 4 (PF4) which activate platelets, leukocytes and the endothelium. This activation explains that low platelet count is associated with thrombotic events in 50% of patients. The diagnosis of HIT is sometimes evoked because of atypical manifestations (i.e. cutaneous necrosis, amnesia, hypotension or dyspnea following intravenous injection of heparin). Biological assays are always necessary to confirm HIT in case of clinical suspicion, and specific rapid tests are now available for detecting anti-PF4 antibodies. However, their specificity is poor and functional assays such as serotonin release assay or platelet aggregation test are often necessary. Argatroban that is a direct antithrombin drug can be used in patients with severe renal failure and will be preferred to danaparoid sodium in this situation. Fondaparinux is not licensed for treating confirmed HIT and can only be used in case of suspicion. The early detection of HIT is based on the monitoring of platelet count recommended in surgical patients receiving a low molecular weight heparin and in all patients treated with unfractionated heparin.

[Management of major bleeding complications and emergency surgery in patients on long-term treatment with direct oral anticoagulants, thrombin or factor-Xa inhibitors. Proposals of the Working Group on Perioperative Haemostasis (GIHP) - March 2013]. / Prise en charge des complications hémorragiques graves et de la chirurgie en urgence chez les patients recevant un anticoagulant oral anti-IIa ou anti-Xa direct. Propositions du Groupe d'intérêt en Hémostase Périopératoire (GIHP) - mars 2013.

New direct oral anticoagulants (NOAC), inhibitors of factor IIa or Xa, are expected to be widely used for the treatment of venous thromboembolic disease, or in case of atrial fibrillation. Such anticoagulant treatments are known to be associated with haemorrhagic complications. Moreover, it is likely that such patients on long-term treatment with NOAC will be exposed to emergency surgery or invasive procedures. Due to the present lack of experience in such conditions, we cannot make recommendations, but only propose management for optimal safety as regards the risk of bleeding in such emergency conditions. In this article, only dabigatran and rivaroxaban were discussed. For emergency surgery at risk of bleeding, we propose to dose the plasmatic concentration of drug. Levels inferior or equal to 30ng/mL for both dabigatran and rivaroxaban, should enable the realization of a high bleeding risk surgery. For higher concentration, it was proposed to postpone surgery by monitoring the evolution of the drug concentration. Action is then defined by the kind of NOAC and its concentration. If the dosage of the drug is not immediately available, proposals only based on the usual tests, PT and aPTT, also are presented. However, these tests do not really assess drug concentration or bleeding risk. In case of severe haemorrhage in a critical organ, it is proposed to reduce the effect of anticoagulant therapy using a nonspecific procoagulant drug (activated prothrombin concentrate, FEIBA, 30-50U/kg, or non-activated 4-factors prothrombin concentrates 50U/kg). For any other type of severe haemorrhage, the administration of such a procoagulant drug, potentially thrombogenic in these patients, will be discussed regarding concentration of NACO and possibilities for mechanical haemostasis.

Use of Haemate(®) P as immune tolerance induction in patients with severe haemophilia A who failed previous induction attempts: a multicentre observational study.

Immune tolerance induction (ITI) can eliminate factor VIII (FVIII) inhibitory antibodies that appear during FVIII replacement therapy. If first-line ITI fails, switching to a different FVIII concentrate, especially one containing von Willebrand factor (VWF), has been advocated. The objective of the study was to assess the efficacy and safety of Haemate(®) P, a plasma-derived FVIII concentrate containing high levels of VWF, as ITI in severe haemophilia A patients who had failed at least one prior ITI attempt with a different FVIII concentrate. In this multicentre, observational study, Haemate(®) P was administered at a starting dose of 83-308 IU kg(-1) day(-1) (1500-6000 IU day(-1)). Efficacy was assessed by standard criteria (e.g. Bethesda titre, FVIII recovery and half-life), and bleeding characteristics. Nine patients from six haemophilia centres were treated with Haemate(®) P after failing one (n = 2), two (n = 5) or three (n = 2) prior ITI courses. The median time from inhibitor detection to Haemate(®) P treatment was 5.4 years. The median Haemate(®) P dose was 134 IU kg(-1), and the median treatment duration 32 months. During median of 47 months of follow-up, complete response, partial response and treatment failure were observed in one, three and five patients respectively. Five patients experienced seven adverse events (AEs), including two serious AEs (sepsis). Haemate(®) P was discontinued due to an AE in one patient with a partial response. Haemate(®) P salvage ITI resulted in complete or partial tolerization in four of nine patients (44%) who had failed previous ITI attempts using different FVIII concentrates.

The IgG autoimmune response in postpartum acquired hemophilia A targets mainly the A1a1 domain of FVIII.

BACKGROUND: Acquired hemophilia A (AHA) is a severe life-threatening autoimmune disease due to the development of autoantibodies that neutralize the procoagulant activity of factor VIII (FVIII). In rare cases, AHA occurs in the postpartum period as a serious complication of an otherwise normal pregnancy and delivery. Due to its rarity, little is known about the features of the antibody response to FVIII in AHA. OBJECTIVES: Our study wanted to (i) determine the epitope specificity and the immunoglobulin (Ig) subclasses of anti-FVIII autoantibodies in plasma samples from a large cohort of AHA patients, and (ii) compare the epitope specificity of anti-FVIII autoantibodies in plasma samples from postpartum AHA and other AHA patients. PATIENTS/METHODS: Seventy-three plasma samples from patients with postpartum AHA (n = 10) or associated with malignancies (n = 16) or autoimmune diseases (n = 11) or without underlying disease (n = 36) were analyzed with three multiplexed assays. RESULTS AND CONCLUSIONS: Our results showed a stronger response against the A1a1-A2a2-B fragments of FVIII and more specifically against the A1a1 domain in patients with postpartum AHA than in the other AHA groups (P < 0.01). Moreover, although IgG4 was the predominant IgG subclass in all groups, anti-A1a1-A2a2-B and anti-A1a1 domain autoantibodies of the IgG(1) and IgG3 subclasses were more frequently detected in postpartum AHA than in the other AHA groups. These findings support the involvement of the Th1-driven response in the generation of autoantibodies in women with postpartum AHA compared with the other groups of AHA patients in whom production of Th2-driven IgG4 was predominant.

Binding of heparin-dependent antibodies to PF4 modified by enoxaparin oligosaccharides: evaluation by surface plasmon resonance and serotonin release assay.

BACKGROUND: The minimal structural requirements of low-molecular-weight heparins that determine the risk of developing heparin-induced thrombocytopenia (HIT) are not fully defined. OBJECTIVES: The ability of enoxaparin-derived oligosaccharides (OS) to induce platelet activation and exposure of platelet-factor 4 (PF4) epitopes recognized by antibodies developed in HIT was studied by surface plasmon resonance (SPR) and serotonin release assay. RESULTS: Decasaccharides with ≥ 11 sulfate groups induced platelet activation in the presence of plasma from patients with confirmed HIT. Serotonin release of > 80% without full inhibition at 100 µg mL(-1) was achieved with decasaccharides containing 14 or 15 sulfate groups, 2 dodecasaccharides and 2 tetradecasaccharides. An SPR method was developed using purified PF4 immobilized on carboxymethylated dextran. Antibodies from all HIT samples bound to PF4/heparin in SPR assays with resonance units (RU) ratio of 109-173 with HIT plasma vs. 88-93 with control plasma. RU ratios > 100 were measured when PF4 was pre-incubated with OS with ≥ 10 saccharide units and one octasaccharide containing 10 sulfate groups. RU ratios > 140, similar to those measured when PF4 was pre-incubated with unfractionated heparin or enoxaparin, were obtained with purified dodeca- and tetradecasaccharides. RU values strongly correlated with the number of sulfate groups in the decasaccharides tested (r = 0.93, P = 0.02). CONCLUSIONS: LMWHs with fragments > 10 saccharides and a large number of sulfate groups are more likely to be associated with a higher risk of HIT. These structure-activity relationships were independent of the ability of the OS to bind antithrombin.

[Specificities of neonatal hemostasis and implications in pathologic situations]. / Particularités de l'hémostase chez le nouveau-né et implications en pathologie.

The haemostasis of healthy newborn differs from those of normal adult but remains well balanced without bleeding or thrombosis. However, this equilibrium is unstable, and the neonate is exposed to acquired or inherited haemostasis disorders that necessitate to be early diagnosed in order to be appropriately treated. Several studies provided reference ranges for haemostatic components in the foetus, the newborn and throughout childhood. The particularities of neonatal haemostasis are therefore better defined and contribute to further understand the pathophysiology and characteristics of hemorrhagic and thrombotic disorders that occur in newborns. Some examples of the impact of age on haemostasis are: the risk of neonatal alloimmune thrombocytopenia is high in the first newborn of a woman at risk since the involved antigens are fully expressed by foetal platelets; the newborn is at risk for vitamin K deficiency with bleeding due to poor transport of vitamin K across the placenta and low levels of coagulation factors II, VII, IX, X; the diagnosis of some inherited coagulation deficiencies can be difficult in the newborn due to physiologically low levels of coagulation factors; thrombotic events are rare in the healthy neonate, despite physiologically very low levels of several coagulation inhibitors; the pharmacokinetic and effects of antithrombotic agents are influenced by the specificities of haemostasis in neonates. This review will discuss about the foetal development of haemostasis until birth, and some implications regarding the pathophysiology, the diagnosis and the treatment of bleeding disorders in the human neonate.