Journal of Thrombosis and Haemostasis最新文献

Background: Antiphospholipid (aPL) antibodies targeting prothrombin are frequently found in Antiphospholipid Syndrome (APS), yet their impact on thrombin generation remains unclear. Prothrombin exists in equilibrium between closed and open conformations, influencing its activation to thrombin. We recently identified POmAb, an aPL antibody that binds the open form and reduces thrombin generation in plasma. However, the in vivo effects of POmAb on coagulation remain unknown.

Aim: To investigate the in vivo effects of POmAb on coagulation.

Methods: In vitro activity was assessed using diluted Russell's viper venom time and chromogenic assays. In vivo effects were evaluated using a laser-induced cremaster arteriole injury model, an inferior vena cava (IVC)-FeCl₃ injury model, and tail bleeding assays. Platelet aggregation was assessed by aggregometry. Prothrombin-binding mechanism was studied by ELISA and surface plasmon resonance.

Results: POmAb inhibited thrombin generation in mouse plasma in vitro. Following intravenous administration at 0.5 mg/kg, POmAb localized rapidly to sites of vascular injury and significantly reduced fibrin formation, with non-significant effects on platelet accumulation and platelet function ex vivo. POmAb reduced clot weights in an IVC thrombosis model, but did not alter tail bleeding times. Binding studies revealed a strong preference for surface-bound versus soluble open prothrombin, explaining its localization and anticoagulant profile at such a low dose.

Conclusions: POmAb exhibits antithrombotic properties in vivo, supporting the potential of POmAb as a novel and safe anticoagulant strategy. Given that POmAb was identified in the context of APS, these findings warrant further investigation into the roles of anti-prothrombin antibodies in APS.

Introduction: Whereas bleeding phenotypes and factor VIII activity (FVIII:C) in hemophilia A (HA) males correlate highly with F8 mutations, FVIII:C in female HA carriers is more variable due to mosaicism arising from a second wild-type F8 allele and X-chromosome inactivation (XCI). Conventionally, only female HA carriers with low FVIII:C were considered at risk for bleeding. Yet hemostatic FVIII:C levels in females remain unestablished. Moreover, HA carriers with normal FVIII:C can also have reproductive tract and other bleeding sequelae. We sought develop a statistical model for predicting abnormal bleeding risk.

Methods: Potential HA carriers were enrolled in an observational cross-sectional study. F8 genotyping confirmed carrier status. Bleeding severity was quantified by bleeding assessment tools. FVIII levels were assessed using one-stage and chromogenic activity assays, as well as FVIII antigen ELISA. XCI skewing was also quantified. Logistic regression analyses were performed to determine the relationship between abnormal bleeding score and covariates.

Results: 62 of 92 adult females are confirmed F8 mutation carriers. 55% of HA carriers have abnormal bleeding (cMCMDM-1 score ≥ 4), despite only 19% with FVIII:C < 40%. Logistic regression modeling incorporating XCI skewing, FVIII antigen and activity, performs better than FVIII:C alone. Highest model performance was seen for carriers with non-severe F8 mutations CONCLUSIONS: Bleeding tendency in HA carriers is common, yet FVIII:C only predicts 38% of those with abnormal bleeding. Logistic regression modeling is highly promising and demonstrates superior performance in predicting bleeding risk compared to baseline FVIII activity alone.

Background: Heparin-induced thrombocytopenia (HIT), vaccine-induced immune thrombocytopenia and thrombosis (VITT), and VITT-like disorders are caused by anti-platelet factor 4 (PF4)/polyanion and/or anti-PF4 IgG antibodies. The rapid anti-PF4/polyanion and anti-PF4 chemiluminescence assays differentiate between typical HIT (anti-PF4/heparin) and VITT antibodies (anti-PF4 antibodies).

Objectives: To characterize monoclonal antibodies(moAbs) and recombinant anti-PF4 antibodies in the two chemiluminescence assays specific for anti-PF4/polyanion and anti-PF4 antibodies, respectively; and to characterize the anti-PF4(/polyanion) antibodies from patients whose sera tested positive in both assays.

Methods: Anti-PF4/heparin and anti-PF4 antibodies: The chimeric moAbs 5B9, 1C12, and 1E12 were generated by standard technology. Recombinant antibodies from VITT and VITT-like patients were generated based on the amino acid sequence of affinity purified patient anti-PF4 antibodies. KKO was humanized (hKKO) by cloning its Fab sequences and expressing it as chimeric recombinant human IgG1 antibody. Anti-PF4 antibodies from patient sera testing positive in both chemiluminescence assays were affinity purified using PF4/polyanion and PF4 beads, respectively.

Results: In chemiluminescence assays, 5B9, hKKO, 1C12 and 1E12 bound to PF4/polyanion complexes but differed largely in their PF4-reactivity. VITT(-like) recombinant antibodies bound only to PF4. Some patients' sera contain antibodies that showed similar reactivity in both assays, regardless, whether purified by PF4/polyanion or PF4 beads, suggesting cross-reactive antibodies, while sera of other patients contained both anti-PF4/heparin and anti-PF4 antibodies.

Conclusions: The different reactivities of monoclonal anti-PF4/heparin antibodies need to be considered when planning experiments and interpreting results. Patients may have very different antibody reactivities despite giving the same results in the two chemiluminescence assays.

Immune thrombocytopenia (ITP) is an acquired bleeding disorder caused by complex immune dysregulation. ITP is a rare disorder with significant morbidity; patients can suffer from bleeding symptoms and reduced quality of life. The pathogenesis of ITP can be observed at several levels: the mechanisms of thrombocytopenia, the loss of tolerance mechanisms, and underlying factors that drive its occurrence. Several mechanisms of platelet destruction and impaired platelet production are recognized as driving the disease. These mechanisms range from autoantibody-mediated platelet destruction, T cell-mediated cytotoxicity, complement-mediated destruction, and platelet desialylation leading to platelet clearance, to thrombopoietin consumption. These alterations are driven by a loss of tolerance with impaired T regulatory and myeloid derived suppressor cell surveillance. Several underlying factors may contribute to ITP pathogenesis by promoting this loss of tolerance, including genetic susceptibility, infections, the gut microbiome, and environmental influences. The numerous alterations described may be heterogeneous across patients with ITP, contributing to disease heterogeneity. Many patients will require treatment of ITP, which may target one or more of these mechanisms, with new therapies being developed to focus on specific pathways. Ultimately, identifying the main mechanism(s) driving ITP in a patient may allow individualized management. This review will highlight the major mechanisms of ITP immunopathology to deepen understanding of important pathways and therapies modulating these pathways.

Background: The incidence of pediatric venous thromboembolism (VTE) is increasing, and research is needed to determine safe and effective thromboprophylaxis strategies.

Objectives: To identify and prioritize key research gaps in pediatric VTE.

Methods: The VTE Risk Factors and Thromboprophylaxis Working Party of the Pediatric and Neonatal Thrombosis and Hemostasis Subcommittee of the International Society on Thrombosis and Haemostasis Scientific and Standardization Committee conducted a crowdsourcing initiative during the 2023 and 2024 ISTH Congresses and via email listservs through the Children's Healthcare Advancements in Thrombosis Consortium and the Venous thromboEmbolism U.S. pediatric subgroup. Respondents identified priority research questions, which were thematically grouped, ranked, and reviewed against current and ongoing research to define future research needs.

Results: Research questions were categorized into four themes: 1) risk factor identification and stratification, 2) advancements in risk assessment models and biomarkers, 3) optimal thromboprophylaxis approaches, and 4) implementation and practice integration. While risk assessment models and select randomized trials have informed prophylaxis in specific pediatric subgroups, evidence gaps remain, particularly in populations excluded from prior studies. Critical unanswered questions include the role of immobility, value of mechanical prophylaxis, optimal anticoagulant selection, dosing, and duration, and strategies to integrate risk-based prophylaxis into diverse care settings.

Conclusions: This initiative defines consensus driven research priorities for pediatric VTE prevention that, when addressed, will support the development of evidence-based clinical practice guidelines for VTE prevention in children.

The path to the development of enoxaparin (Lovenox/Clexane), one of the most widely used low molecular weight heparins (LMWH) worldwide, was far from smooth. This narrative review, presented from the personal perspective of the senior author who lived this journey, describes the pivotal research conducted at McMaster University in Canada that transformed enoxaparin from a promising laboratory compound into a cornerstone of prevention and treatment of thrombosis. The story begins in the late 1970s with the observation that a LMWH, produced through controlled depolymerization, exhibited comparable antithrombotic efficacy to unfractionated heparin with a reduced risk of bleeding in animal models. It ends in the 1990s with the successful evaluation in clinical trials and the regulatory approval of enoxaparin for the prevention of deep vein thrombosis after orthopedic surgery.

Background: Post-thrombotic syndrome (PTS) is a common complication of deep vein thrombosis (DVT) of the lower extremities, associated with reduced quality of life and high healthcare costs. No reliable estimates exist of PTS risk by DVT location and its burden in the general population.

Objectives: To estimate: (1) the risk of PTS by anatomical location of DVT; (2) the age- and sex-specific incidence and prevalence of PTS in Europe.

Methods: We performed a systematic review and mixed-effects meta-analysis of studies reporting the cumulative incidence of PTS defined by Villalta score in patients with iliofemoral, femoropopliteal, and distal DVT. We then applied location-specific risk estimates to age- and sex-specific European DVT incidence data using a life table approach with Monte Carlo simulations to calculate the annual incidence and prevalence of PTS.

Results: Among 49 studies (N=14 171, 15 interventional, 34 observational), estimated PTS risk was 51.1% (95%CI: 39.5-62.7%) for iliofemoral, 30.7% (21.4-39.9%) for femoropopliteal, and 22.8% (17.1-29.8%) for distal DVT, assuming no systematic use of compression stockings for proximal DVT. We estimate 250 000 (95%CI: 220 000-315 000) new PTS cases annually in Europe (incidence 0.34 [0.29-0.42] per 1 000), and 4.86 million (4.11-5.88) prevalent cases (prevalence 6.5 [5.5-7.9] per 1 000).

Conclusion: PTS risk increases with proximal DVT extent. Approximately 5 million individuals in Europe are estimated to live with PTS, underscoring the need for targeted prevention and treatment strategies.

Introduction: Despite the global burden of disseminated intravascular coagulation (DIC) and decades of scoring-system development, no international assessment has evaluated global current practices among clinicians.

Methods: The International Society on Thrombosis and Hemostasis (ISTH) Scientific Standardization Subcommittee (SSC) on DIC conducted an international survey (Mar 2024-Feb 2025) to assess global diagnostic and treatment practices. Data was analyzed in light of participants' country level based on world bank classification RESULTS: A total of 153 clinicians from 27 countries completed the survey. Most respondents were from high-income countries (64%). The most suggestive clinical features of DIC were bleeding (89%), petechiae (77%), and shock (63%). Standard laboratory tests were commonly used (platelet count 93%, PT/INR 85%, fibrinogen 78%), but middle-income countries had reduced access to fibrinogen testing, serial monitoring, and advanced diagnostics. Only 28% of clinicians used a formal scoring system (ISTH 21%, SIC 14%) despite 76% reporting familiarity with the ISTH definition. First-line treatments most often included fresh frozen plasma (65%), platelets (38%), cryoprecipitate (32%), and whole blood (24%), with marked resource-driven differences between high- and middle-income countries. Major challenges included difficulty diagnosing DIC due to variable underlying disorders (59%) and clinical heterogeneity (47%), along with significant resource constraints, particularly in middle-income regions (limited test availability 57%, inadequate transfusion supply 54%, lack of critical care support 38%).

Conclusion: Despite strong global awareness, major gaps persist between recommended and real-world DIC practice, particularly in resource-limited settings. Expanding access to diagnostics, supporting guideline-based management, and developing innovative tools - including AI-driven models- are needed.

Background: All hospital laboratories in Sweden use the Owren prothrombin time (PT) method primarily to monitor anticoagulant treatment. Direct international normalised ratio (INR) calibration was introduced in 1999 under the supervision of Equalis, the national organisation for external quality assessment (EQA) in laboratory medicine. We present 25 years of combined experience in developing a national calibration procedure and conducting EQA of INR.

Methods: Since the introduction of direct INR calibration, 14 different Equalis INR calibrator kits have been produced. Variability between laboratories and different reagents and calibrator lots have been determined (>51 000 results, 96 EQA materials). The stability of the calibrators and the calibration procedure were studied from remeasurements of calibrators, weekly warfarin dosing in patient records and a comparison study with an international reference thromboplastin (RBT/05).

Results: Interlaboratory variability was improved significantly after the introduction of direct INR calibration. Results were consistent over 25 years, with mean coefficient of variation (CV) < 6% in the therapeutic range. The INR calibrators showed reproducible measured results, and the calibration procedure has been stable over time. Furthermore, anticoagulated patients had a stable mean weekly dose of warfarin in relation to mean INR. The Owren's PT agrees with Quick PT in a direct comparison with RBT/05.

Conclusions: There is a good agreement between the PT measurements in Swedish laboratories, and non-significant reagent differences. The user-friendly and unique calibration procedure, including the preparation of certified plasmas, improved the performance of the national PT measurements and was also proved to be stable over decades.