Thrombin generation and whole blood viscoelastic assays in the management of hemophilia: current state of art and future perspectives

Shifting Landscape of Hemophilia Therapy: Implications for Current Clinical Laboratory Coagulation Assays

Clinical coagulation assays are an integral part of diagnosing and managing patients with hemophilia; however, in this new era of bioengineered factor products and non-factor therapeutics, problems have arisen with use of traditional coagulation tests for the quantification of several of these new products. Discussion over the use of one-stage clotting assays versus chromogenic substrate assays for clinical decision making and potency labeling has been ongoing for many years. Emerging factor concentrates have heightened concern over assay selection and availability. Emicizumab interferes with all aPTT based assays, rendering them unreliable and potentially falsely reassuring to the unaware provider. This review explores considerations for coagulation assays in the clinical setting and highlights how awareness of institutional coagulation assays and potential limitations have never been more critical for providers caring for patients with bleeding disorders. This article is protected by copyright. All rights reserved.

Evaluation of recombinant factor VIII Fc (Eloctate) activity by thromboelastometry in a multicenter phase 3 clinical trial and correlation with bleeding phenotype

The aim of this study was to compare the hemostatic efficacy of recombinant factor VIII Fc (rFVIIIFc) (Eloctate) and Advate by ex-vivo rotation thromboelastometry (ROTEM) of whole blood and to explore potential ROTEM parameters that may be more predictive of a patient's bleeding tendency than plasma FVIII activity. Thirteen clinical sites were selected to perform ROTEM on freshly collected blood samples from 44 patients in the phase 3 study for rFVIIIFc, including 16 patients undergoing sequential pharmacokinetic assessment of Advate and rFVIIIFc. Equivalent hemostatic activity was observed for rFVIIIFc and Advate in postinfusion samples, followed by improvements for rFVIIIFc in clotting time, clot formation time and alpha angle (α) for a longer duration than Advate, consistent with the pharmacokinetic improvements reported previously for rFVIIIFc. Our study did not demonstrate a statistical correlation between a patient's ROTEM activity at baseline or at trough and the occurrence of spontaneous bleeds while on prophylactic therapy. However, an association was observed between postinfusion clotting time and the occurrence of one or more spontaneous bleeds vs. no bleeds over a follow-up period of 1 year (P = 0.003). How well a patient's whole blood clotting deficiency is corrected after a dose of FVIII may be an indicator of subsequent bleeding tendency in patients with otherwise equivalent FVIII peak and trough levels. The technical challenges of standardizing the ROTEM, largely overcome in the current study, may however preclude the use of this method for widespread assessment of global hemostasis unless additional assay controls or normalization procedures prove to be effective.

Nano- and micro-materials in the treatment of internal bleeding and uncontrolled hemorrhage

Internal bleeding is defined as the loss of blood that occurs inside of a body cavity. After a traumatic injury, hemorrhage accounts for over 35% of pre-hospital deaths and 40% of deaths within the first 24 hours. Coagulopathy, a disorder in which the blood is not able to properly form clots, typically develops after traumatic injury and results in a higher rate of mortality. The current methods to treat internal bleeding and coagulopathy are inadequate due to the requirement of extensive medical equipment that is typically not available at the site of injury. To discover a potential route for future research, several current and novel treatment methods have been reviewed and analyzed. The aim of investigating different potential treatment options is to expand available knowledge, while also call attention to the importance of research in the field of treatment for internal bleeding and hemorrhage due to trauma.

Viscoelastic Monitoring to Guide Hemostatic Resuscitation in Liver Transplantation Surgery

Coagulopathic bleeding must be anticipated during liver transplantation (LT) surgery. Patients with end-stage liver disease (ESLD) often present with disease-related hematologic disturbances, including the loss of hepatic procoagulant and anticoagulant clotting factors and thrombocytopenia. Transplantation surgery itself presents additional hemostatic changes, including hyperfibrinolysis. Viscoelastic monitoring (VEM) is often used to provide targeted, personalized hemostatic therapies for complex bleeding states including cardiac surgery and major trauma. The use in these coagulopathic conditions led to its application to LT, although the mechanisms of coagulopathy in these patients are quite different. While VEM is often used during transplant surgeries in Europe and North America, evidence supporting its use is limited to a few small clinical studies. The theoretical and clinical applications of the standard and specialized VEM assays are discussed in the setting of LT and ESLD.

Clot waveform analysis: Where do we stand in 2017?

Analysis of the optical waveform generated during global coagulation assays, such as activated partial thromboplastin time and prothrombin time, can provide much precious information on the global coagulation state of the plasma sample tested, in addition to a single clotting time. Many studies have been published concerning patient diagnosis and management in haemophilia A, and in the early diagnosis and prognosis of disseminated intravascular coagulation and sepsis. However, many other works have also been published on further potential clinical applications such as lupus anticoagulant diagnosis and anticoagulant monitoring. Altogether, these publications have demonstrated the ability for clot waveform analysis (CWA) to improve patient management, especially as this tool is inexpensive, rapid and readily available on coagulation analysers with optical detection systems. By an extensive review of the literature related to studies performed on CWA, this publication aims at providing a review of current knowledge in this specific field, ranging from research data to potential clinical applications and future trends.

Low thrombin generation predicts poor prognosis in ischemic stroke patients after thrombolysis

Thrombolysis by intravenous recombinant tissue plasminogen activator (rt-PA) is an effective therapy in acute ischemic stroke (AIS). Thrombin generation test (TGT) is a global hemostasis test providing information about the speed and amount of generated thrombin in plasma. Here we aimed to find out whether results of this test before the initiation of thrombolysis might predict outcomes. Study population included 120 consecutive AIS patients, all within 4.5 hours of their symptom onset, who underwent thrombolysis by rt-PA. Blood samples were collected from all patients upon admission and TGT was performed using platelet poor plasma. Clinical data of patients including the NIHSS were registered at admission, day 1 and 7 after therapy. The ASPECT score was assessed using CT images taken before and 24 hours after thrombolysis. Long-term functional outcome was defined 3 months after the event by the modified Rankin Scale. Endogenous Thrombin Potential (ETP) and Peak Thrombin were significantly lower in patients with cardioembolic IS. Symptomatic intracranial hemorrhage (SICH) was found in 6 patients and was significantly associated with low ETP and Peak Thrombin levels. A multiple logistic regression model revealed that an ETP result in the lower quartile is an independent predictor of mortality within the first two weeks (OR: 6.03; 95%CI: 1.2–30.16, p<0.05) and three months after the event (OR: 5.28; 95%CI: 1.27–21.86, p<0.05). Low levels of ETP and Peak Thrombin parameters increase the risk of therapy associated SICH. A low ETP result is an independent predictor of short- and long-term mortality following thrombolysis.

Combination of hemostatic therapies for treatment of patients with hemophilia A and inhibitors

BACKGROUND

Therapy application and monitoring of patients with hemophilia A (HA) and inhibitors are challenging. In the current study, combined FVIII - bypass therapy was implemented for a cohort of severe HA patients with inhibitors.

METHODS

Plasma of 15 HA patients with inhibitors was spiked ex vivo with FVIII, rFVIIa, FEIBA and their combinations and thrombin generation (TG) was studied. Some patients who experienced hemarthroses or required minor surgeries were treated by a combined concomitant administration of FVIII+FEIBA as IV bolus doses.

RESULTS

TG spiking studies showed individual responses not correlated to inhibitor titer. Combinations of agents augmented TG as compared to any single agent, while combined FVIII+FEIBA yielded the highest TG, supporting it as a potential treatment. Following emergent successful surgery of child treated by concomitant FVIII+FEIBA, a total of 396 episodes in 7/15 patients were treated with concomitant FVIII+FEIBA. Five patients were treated for bleeding episodes only, whereas 2 were children undergoing immune tolerance induction (ITI) with FEIBA prophylaxis. Four minor surgeries were performed on FVIII+FEIBA repeated infusions. Neither thrombosis nor any other adverse events were documented.

CONCLUSION

A combination of FVIII+FEIBA may be effective and safe as an alternative treatment option for some high-responding inhibitor patients.

Biochemical characterization of LR769, a new recombinant factor VIIa bypassing agent produced in the milk of transgenic rabbits

BACKGROUND

The bypassing agent factor VII (FVIIa) is a first-line therapy for the treatment of acute bleeding episodes in patients with haemophilia and high-titre inhibitors. FVIIa is a highly post-translationally modified protein that requires eukaryotic expression systems to produce a fully active molecule. A recombinant FVIIa was produced in the milk of transgenic rabbits to increase expression and provide an efficient, safe and affordable product after purification to homogeneity (LR769).

AIM

To present the biochemical and functional in vitro characteristics of LR769.

RESULTS

Mass spectrometric analyses of the intact protein and of heavy and light chains revealed a fully activated, mature and properly post-translationally modified protein notably regarding N/O-glycosylations and γ-carboxylation. Primary structure analysis, performed by peptide mapping, confirmed 100% of the sequence and the low level or absence of product-derived impurities such as oxidized, deamidated and glycated forms. Low levels of aggregates and fragments were observed by different chromatographic methods. Higher order structure investigated by circular dichroism showed appropriate secondary/tertiary structures and conformational change in the presence of Ca²⁺ ions. Finally, activated partial thromboplastin time and thrombin generation assays showed the ability of LR769 to decrease coagulation time and to generate thrombin in haemophiliac-A-plasmas, even in the presence of inhibitors.

CONCLUSION

The innovative expression system used to produce LR769 yields a new safe and effective rhFVIIa for the treatment of haemophilia A or B patients with inhibitors.

Simultaneous viscosity and density measurement of small volumes of liquids using a vibrating microcantilever

Many industrial and technological applications require precise determination of the viscosity and density of liquids. Such measurements can be time consuming and often require sampling substantial amounts of the liquid. These problems can partly be overcome with the use of microcantilevers but most existing methods depend on the specific geometry and properties of the cantilever, which renders simple, accurate measurement difficult. Here we present a new approach able to simultaneously quantify both the density and the viscosity of microliters of liquids. The method, based solely on the measurement of two characteristic frequencies of an immersed microcantilever, is completely independent of the choice of a cantilever. We derive analytical expressions for the liquid's density and viscosity and validate our approach with several simple liquids and different cantilevers. Application of our model to non-Newtonian fluids shows that the calculated viscosities are remarkably robust when compared to measurements obtained from a standard rheometer. However, the results become increasingly dependent on the cantilever geometry as the frequency-dependent nature of the liquid's viscosity becomes more significant.

Global clotting assays - monitoring the effect of by-passing agents in haemophilia patients with inhibitors

The development of FVIII/FIX inhibitor alloantibodies represents a severe complication requiring specific laboratory evaluation for establishing a life-saving therapy regimen. Our preliminary study aimed at elaborating a laboratory strategy for monitoring the effectiveness of Activated Prothrombin Complex Concentrate (APCC) and recombinant activated factor VII (rFVIIa) in haemophiliacs with inhibitors, by checking the reliability and clinical value of three complementary assays: clotting-time based coagulometry, thrombelastography (TEG) and thrombin generation assay (TGA). The investigations were performed on 7 patients with severe haemophilia A with high titer inhibitors treated for 12 episodes of severe bleedings, 5 of them for surgical interventions. After the administration of bypassing agents (BPAs) the clotting-time based assay brought changes only on prothrombin (p<0.01), potentially signaling a thrombotic risk, without any impact on the global hemostasis. TEG displayed prompt significant improvement only after rFVIIa (90μg/kg). TGA revealed significantly improved values for peak and velocity index, time to peak and start tail after both BPAs. Despite some disparities between biological hemostatic phenotype and clinical response to therapy, we concluded that TEG and TGA are the only current exploratory assays, expressing the quality of haemostatic control, representing a real support for a personalized, adapted therapy in hemophilia with inhibitors.

Perioperative Coagulation Management of a Hemophilia A Patient During Cardiac Surgery

Perioperative management of cardiovascular surgical procedures requiring cardiopulmonary bypass (CPB) in patients with hemophilia A poses a clinical challenge in coagulation management. Use of CPB requires the administration of an anticoagulant, usually unfractionated heparin, and also causes dilutional coagulopathy, platelet dysfunction or platelet consumption coagulopathy. Hypothermia and activation of the inflammatory cascade also affect coagulation. The effects of CPB on circulating levels of factor VIII have not been clearly defined. In this review, the effects of CPB and hemodilution on FVIII are shown in a case presentation, and perioperative laboratory testing in patients with hemophilia A having cardiac surgery is discussed along with perioperative and postoperative coagulation management.

Rare bleeding disorders-old diseases in the era of novel options for therapy

Rare diseases are defined as life-threatening or chronically debilitating diseases with a prevalence of less than one per 2000 according to the European Union or one per 1250 according to the USA. Congenital rare bleeding disorders RBD are reported in most populations, with incidence varying from 1 in 5000 (Hemophilia A), 1:30,000 (Hemophilia B) to much rarer (1:500,000 for FVII deficiency, 1-3 million for Prothrombin or FXIII deficiency). Acquired Hemophilia A is also a rare bleeding disorder with estimated frequency of 1 in million. Most RBDs are inherited as autosomal recessive (AR); however, heterozygous carriers with varying degrees of corresponding factor deficiency may render an unpredictable propensity for bleeding. In patients with bleeding symptoms, laboratory assessment and especially molecular techniques currently enable accurate diagnosis and may provide tools for prenatal and family counseling. Currently hemostasis control is mainly based upon replacement of the missing coagulation factors (unless presence of inhibitors renders it impossible), however future gene therapy and disruptive, non-replacement alternatives may be promising for patients with RBD.

Single-platelet nanomechanics measured by high-throughput cytometry

Haemostasis occurs at sites of vascular injury, where flowing blood forms a clot, a dynamic and heterogeneous fibrin-based biomaterial. Paramount in the clot's capability to stem haemorrhage are its changing mechanical properties, the major drivers of which are the contractile forces exerted by platelets against the fibrin scaffold. However, how platelets transduce microenvironmental cues to mediate contraction and alter clot mechanics is unknown. This is clinically relevant, as overly softened and stiffened clots are associated with bleeding and thrombotic disorders. Here, we report a high-throughput hydrogel-based platelet-contraction cytometer that quantifies single-platelet contraction forces in different clot microenvironments. We also show that platelets, via the Rho/ROCK pathway, synergistically couple mechanical and biochemical inputs to mediate contraction. Moreover, highly contractile platelet subpopulations present in healthy controls are conspicuously absent in a subset of patients with undiagnosed bleeding disorders, and therefore may function as a clinical diagnostic biophysical biomarker.

Thromboelastography (TEG)

Thromboelastography (TEG) has been used for decades to guide transfusion therapy during cardiac and hepatic surgeries. Renewed interest and improved technology have led to wider applications of TEG in other areas of hemostasis. To correctly interpret the data generated and to validate outcomes, it is important to improve the understanding of the differences in the currently available assay procedures, the issues related to sample activation, and the importance of the use of appropriate controls. Current TEG assays use a variety of samples and can vary slightly in the procedures. In this chapter, we very briefly review TEG applications and discuss interpretations, normal ranges, and reference controls, and we explain the method of TEG run using standard citrated native blood samples. We provide detailed technical steps and tips. We discuss precautions and issues related to the assay, which we hope can guide toward better application and data interpretation.

The utility of thromboelastography in inherited and acquired bleeding disorders

Thromboelastography (TEG) was first described by Hartert in 1948, and was designed to monitor viscoelastic clot strength in whole blood in real time. The current TEG method and Rotational Thromboelastometry (ROTEM) were subsequently developed from the original principles. Both of the modern methods provide data by measuring changes in the viscoelastic strength of a small sample of clotting blood in response to a constant rotational force. The important advantage of these techniques is to visually observe and quantify blood coagulation including the propagation, stabilization and dissolution phases of clot formation under low shear conditions. Analysis of the results provides detailed kinetic data on fibrin generation, clot strength and fibrinolysis. These TEG/ROTEM analyses therefore enable evaluation of global clotting function and the monitoring of haemostatic treatment in various clinical situations, not only in patients with genetic bleeding disorders, such as haemophilia, but also in patients undergoing cardiac surgery, liver transplantation or suffering from traumatic injury. Some evidence suggests that haemostatic management using TEG/ROTEM leads to a reduction in total transfusions of whole blood or clotting factors. Wider clinical application of this technology seems likely.

Comparative biochemical studies of fresh frozen plasma and pooled solvent/detergent-treated plasma (octaplasLG® ) with focus on protein S and its impact in different thrombin generation assay set-ups

BACKGROUND AND OBJECTIVES

The solvent/detergent treatment enables effective and robust inactivation of all lipid-enveloped viruses, but also inactivates partly sensitive plasma proteins such as protein S. The aim of this study was to investigate the thrombin generation capacity of octaplasLG^® , in particular focusing on the function of protein S in thrombin generation assay and the impact of assay settings.

MATERIALS AND METHODS

Sixteen octaplasLG^® batches and 32 units of single donor fresh frozen plasma (FFP) were investigated. For protein S, both functional activity and free antigen levels were measured. Thrombin generation assay was performed using two fluorogenic tests with different triggers. Finally, rotational thromboelastometry was performed.

RESULTS

Mean protein S levels were lower in octaplasLG^® , but a wider range of values was found for FFP. Clotting parameters and thrombin generation capacities overlapped between the two plasma groups as demonstrated using both thrombin generation assays and different triggers. Spiking studies with protein S-depleted plasma, human purified protein S or antibodies against protein S confirmed a correlation between protein S and thrombin generation capacity under specific assay conditions, especially in an assay with low tissue factor concentration.

CONCLUSION

Correlation between protein S and thrombin generation capacity was demonstrated in the TGA. Due to higher variability in protein S content in the FFP group, overlapping haemostatic potentials of the two plasma groups were found.

Challenges of diagnosing and managing the adolescent with heavy menstrual bleeding

Unpredictable, prolonged or heavy menstrual bleeding (HMB) may be expected for many adolescents soon after menarche. A decade of clinical experience and research has now established firmly that bleeding disorders (BD) are common in adolescents with HMB. Despite these advances, many questions remain, and several aspects of the diagnosis and management of BDs in adolescents are not supported by rigorous clinical trials. In this overview, four major areas will be discussed. First, we will discuss the frequency of BDs in young women with HMB. Up to 20% of older females with HMB are thought to have an underlying BD. Estimates from retrospective studies in adolescents suggest a prevalence that varies anywhere from 10 to 62%. Prospective studies with uniform hemostatic evaluation are needed to answer this question definitively. Second, we will review existing tools that help screen and diagnose adolescents with HMB with an underlying BD. Although identification of an underlying BD in older women with HMB is relatively straight forward, uncertainties remain for adolescents. Heavy menstrual bleeding in this age group may have different pathophysiological underpinnings than those in older women and may often be disregarded as anovulatory. There is an urgent need to develop novel tools, and evaluate existing diagnostic strategies in adolescents. Third, we will discuss the optimal medical management of HMB in young adolescents. As direct evidence is largely lacking, these areas are also subject to extrapolation from older women. Lastly, an important area- prediction, and management of future bleeding in those adolescents who are diagnosed with a mild BD-will be discussed. Throughout, areas of controversy and opportunities for further research are highlighted.

Exploring potential anticoagulant drug formulations using thrombin generation test

Many anticoagulant drugs inhibiting proteins of the coagulation cascade have been developed. The main targets of anticoagulant drugs are thrombin and factor Xa; inhibiting these factors delays thrombus growth, thus preventing thrombosis while increasing bleeding risk. A balance between thrombosis and bleeding is ensured in the ‘therapeutic window’ of the anticoagulant drug concentration range. Novel anticoagulant drugs and combinations thereof are being developed. We rank coagulation factors as potential anticoagulant drug targets in combination with thrombin inhibitors, aptamer HD1 and bivalirudin, providing a background for several promising dual target treatment strategies.

The thrombin generation test was used to assess the whole coagulation cascade in normal and factor-deficient human blood plasma. Potential therapeutic windows were estimated for coagulation factors, ranking them as targets for anticoagulant drugs. Thrombin and factor Xa have been revealed as the most promising targets, which fully agrees with the current drug development strategy. Inhibitors of factors Va and VIIa are expected to have narrow therapeutic windows. Inhibitors of factors VIIIa and IXa are expected to have a moderate anticoagulant effect. Factors XI and XII are poor targets for anticoagulant drugs. Compared with plasma that is deficient in factor II, the thrombin inhibitors bivalirudin and aptamer HD1 had increased activity. Both inhibitors were tested in deficient plasma providing a model of potential drug combination. The most promising combinations were anti-thrombin with anti-V/Va and also anti-thrombin with anti-IX/IXa. Each combination had an incremental dose-effect dependence that is promising from the standpoint of the therapeutic window.

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Coagulation factors are ranked as anticoagulant targets.

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Several promising combinations of anticoagulant and thrombin inhibitor are proposed.

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The most promising combinations are anti-thrombin with anti-V/Va or anti-IX/IXa.

Epithelial and Erythrocyte Microvesicles From Bronchoalveolar Lavage Fluid Are Elevated and Associated With Outcome in Chronic Lung Allograft Dysfunction

BACKGROUND

Chronic lung allograft dysfunction (CLAD) is the major outcome limitation for lung transplant recipients (LTR) after the first year, and therapies targeting immunological pathways show only limited success. Because microvesicles (MV) are biomarkers of endothelial dysfunction and coagulation but are also involved in immunological responses, we hypothesized that MV, found in bronchoalveolar lavage (BAL) fluids (BALF) of LTR at CLAD diagnosis, are elevated and potential prognostic biomarkers.

METHODS

The BALF was collected from 37 LTR at time point of CLAD diagnosis and 37 LTR without any complication at routinely performed BAL. The MV concentration and origin were determined by flow cytometry by detection of different antigens. Patient- and transplant-related risk factors were included in a retrospective statistical analysis.

RESULTS

The BALF-MV levels of epithelial and red blood cell (RBC) origin were significantly higher in CLAD patients (mean: 1533/μL and 158/μL) compared to controls (436/μL, 57/μL). The LTR with high levels of epithelial MV >580/μL showed a significantly shorter overall survival at 4 years after BAL (39.5%) compared to patients with low MV (66.4%) and this proofed to be an independent prognostic factor in multivariate Cox analysis (hazards ratio = 3.05). Furthermore, LTR with high levels of RBC MV ≥225/μL were also associated with worse disease-specific survival, with probabilities at 4 years after BAL of 85.8% vs. 36.0%.

CONCLUSIONS

Epithelial and RBC BALF-MV are elevated at CLAD diagnosis, have a potential as biomarkers, and support the hypothesis of a pathway, including activation of coagulation and complement, endothelial barrier dysfunction, and microangiopathy.

Comparison of platelet-derived and plasma factor VIII efficacy using a novel native whole blood thrombin generation assay

BACKGROUND

We have recently developed a successful gene therapy approach for hemophilia A in which factor VIII (FVIII) expression is targeted to platelets by the αIIb promoter. Levels of platelet-expressed FVIII (2bF8) achieved by gene therapy may vary between individuals due to differences in ex vivo transduction and gene expression efficiency. Accurate assays to evaluate 2bF8 efficacy are desirable.

OBJECTIVE

To compare the hemostatic efficacy of 2bF8 with replacement therapy over a wide therapeutic dose range.

METHODS

Efficacy of 2bF8 was assessed using a new transgenic mouse model expressing high 2bF8 levels (LV18(tg) ). Blood from LV18(tg) mice or FVIII(null) mice infused with recombinant FVIII was mixed with FVIII(null) blood at different ratios ex vivo to achieve several concentrations of 2bF8 or plasma FVIII. Samples were evaluated with a novel native whole blood thrombin generation assay that uses recalcified whole blood without the addition of tissue factor to initiate coagulation.

RESULTS

FVIII dose dependency was observed in all five thrombin generation parameters. While the total amount of thrombin generated was similar, 2bF8 significantly accelerated thrombin generation compared with plasma FVIII. Remarkably, a 10-fold lower dose of 2bF8 than plasma FVIII (0.2% vs. 2%) significantly shortened the onset and peak of thrombin generation compared with FVIII(null) blood.

CONCLUSION

Using a new transgenic mouse model, we showed that the novel native whole blood thrombin generation assay established here can be used to monitor platelet targeted FVIII gene therapy. The higher therapeutic efficacy of 2bF8 compared with factor replacement therapy seemed to be due to acceleration of thrombin generation.

Challenges in hemophilia care in Australia and New Zealand

BACKGROUND

Health and life expectancy for people with hemophilia have improved significantly in recent years, but we face new challenges, especially in the context of resource-constrained health services.

AIM

This paper aims to highlight such challenges and propose practical solutions.

METHODS

Nine hemophilia specialists from Australia and New Zealand reached consensus on areas of greatest need for improvement in hemophilia care in these countries, based on clinical experience and published data, and agreed on how to address these.

RESULTS

Demography, optimizing treatment and assessing treatment success were identified as broad areas of challenge which included: comorbidities in ageing patients; transitioning from pediatric to adult care; equity of care for remote populations; weight-based dosing in obese patients; tailoring prophylaxis; accurate diagnosis of acute joint pain; managing chronic arthropathy; providing psychosocial support; consistency in definitions and assessment; and quantifiable outcome measures. Practice points included increased cross-specialty coordination and including psychologists and rheumatologists as part of comprehensive care teams; close collaboration between pediatric and adult centers to facilitate transition of care; systems such as telehealth that ensure continuity of care for remote populations; using pharmacokinetic data to tailor therapy; rapid and accurate diagnosis of acute joint pain; using data from bleeding registries to assess treatment effects and help with service planning; and ensuring consistency through benchmarking and standardization of HTCs.

SUMMARY

Achieving treatment equity, optimal outcomes and cost savings may be possible through investing in national governance structures, expanding the comprehensive model of care and implementing innovative solutions tailored to local needs.

Global assays in hemophilia

The quest for the ideal method to study hemostasis in the evaluation and management of patients with bleeding disorders such as hemophilia is an ongoing effort. With the rapid evolution of biotechnology and the emergence of several new products for treatment of patients with hemophilia with and without inhibitors, there is a great need for tests that can be used to reliably evaluate and monitor our interventions. Global assays in coagulation allow the study of the interaction between the components involved in the process of hemostasis and are therefore considered by many to be more reflective of the in vivo hemostatic mechanism. Here we provide a brief review of the most widely used global assays in hemostasis (thrombin generation and thromboelastography) and their utility in the evaluation and management of hemophilia.

[Mild hemophilia A fortuitously discovered during Henoch-Schönlein purpura]

Henoch-Schönlein purpura is a common form of immunological vasculitis in children. Hemophilia A is a genetic disorder, inherited in a X-linked recessive pattern, and characterized by spontaneous hemorrhage or prolonged bleeding due to factor VIII deficiency. The clinical signs depend on the severity of factor VIII deficiency. We herein report the case of a 4-year-old boy admitted to the emergency room for typical rheumatoid purpura, associated with a lengthening of aPTT, whose exploration had uncovered mild hemophilia A. Laboratory assays should explore lengthening of aPTT: firstly the presence of lupus anticoagulant without bleeding risk, in an inflammatory context; secondly a deficiency of VWF and one of the factors involved in the extrinsic coagulation pathway associated with bleeding risk.

Managing Haemophilia for Life: 5th Haemophilia Global Summit

The 5th Haemophilia Global Summit was held in Barcelona, Spain, in September 2014. The programme was designed by an independent Scientific Steering Committee of haemophilia experts and explored issues relevant to the practical management of haemophilia, as well as key opportunities and challenges for care in the future. The topics outlined in this supplement were selected by the Scientific Steering Committee for their relevance to improving haemophilia care globally. In this supplement from the meeting, Gerry Dolan explores pharmacokinetics and dynamics in haemophilia, and Gerry Dolan and Ian Jennings jointly address the role of the laboratory in haemophilia care. The potential benefits of low-dose prophylaxis regimens for people with haemophilia in the developing world are reviewed by Jerzy Windyga, and the question of whether 'Future haemophilia research should be undertaken in the developing world' is debated by Jerzy Windyga and Cedric Hermans. Management strategies for ankle arthropathy are discussed by Sébastien Lobet and E. Carlos Rodríguez-Merchán, and the use of ultrasound for the early detection of haemophilic arthropathy is addressed by Matteo Nicola Dario Di Minno and Víctor Jiménez-Yuste. Finally, the role of patients in the future of haemophilia care is reviewed by Brian O'Mahony.

Correction of human hemophilia A whole blood abnormalities with a novel bypass agent: zymogen-like FXa(I16L)

BACKGROUND

Approximately 30% of hemophilia A (HA) and 5% of hemophilia B patients develop inhibitors to protein replacement therapy, and this is the major cause of disease-related morbidity in the developed world. We previously developed zymogen-like factor Xa (FXa) molecules with impaired active site maturation, enabling a greater half-life than wild-type FXa while maintaining full procoagulant function in the prothrombinase complex. Here we evaluated the ability of zymogen-like FXa(I16L) to correct whole blood thromboelastometry abnormalities of severe HA subjects with and without inhibitors.

METHODS

Fourteen severe HA subjects without and five with inhibitors were enrolled at baseline (

FVIII

C < 1%) > 5 half-lives from factor or bypass therapy. The subjects' whole blood was evaluated by thromboelastography (ROTEM(®) ) using INTEM analysis with two concentrations of FXa(I16L) or recombinant factor VIIa (rFVIIa).

RESULTS

With 0.1 nm FXa(I16L) , clot time (CT, in minutes [min]) among HA subjects without and with inhibitors (mean = 2.87 min, 95% CI = 2.58-3.15 min, and mean = 2.9 min, 95% CI = 2.07-3.73 min, respectively) did not significantly differ from control CT (mean = 2.73 min, 95% CI = 2.62-2.85 min). Addition of 20 nm rFVIIa, simulating a 90-μg/kg dose, resulted in significantly prolonged CTs for HA subjects without and with inhibitors (mean = 5.43 min, 95% CI = 4.53-6.35 min, and mean = 4.25 min, 95% CI = 3.32-5.17 min, respectively) relative to controls.

CONCLUSIONS

FXa(I16L) restored thromboelastometry CT to control values in severe HA subjects with and without inhibitors. The findings corroborate previous animal data and demonstrate the first evidence of zymogen-like FXa(I16L) correcting human HA subjects' whole-blood abnormalities and support the use of FXa(I16L) as a novel hemostatic agent.

Using a Systems Pharmacology Model of the Blood Coagulation Network to Predict the Effects of Various Therapies on Biomarkers

A number of therapeutics have been developed or are under development aiming to modulate the coagulation network to treat various diseases. We used a systems model to better understand the effect of modulating various components on blood coagulation. A computational model of the coagulation network was built to match in-house in vitro thrombin generation and activated Partial Thromboplastin Time (aPTT) data with various concentrations of recombinant factor VIIa (FVIIa) or factor Xa added to normal human plasma or factor VIII-deficient plasma. Sensitivity analysis applied to the model revealed that lag time, peak thrombin concentration, area under the curve (AUC) of the thrombin generation profile, and aPTT show different sensitivity to changes in coagulation factors' concentrations and type of plasma used (normal or factor VIII-deficient). We also used the model to explore how variability in concentrations of the proteins in coagulation network can impact the response to FVIIa treatment.

Disease Severity Correlates with Thrombotic Capacity in Experimental Nephrotic Syndrome

Thrombotic disease, a major life-threatening complication of nephrotic syndrome, has been associated with proteinuria and hypoalbuminemia severity. However, it is not fully understood how disease severity correlates with severity of the acquired hypercoagulopathy of nephrotic syndrome. Without this knowledge, the utility of proteinuria and/or hypoalbuminemia as biomarkers of thrombotic risk remains limited. Here, we show that two well established ex vivo hypercoagulopathy assays, thrombin generation and rotational thromboelastometry, are highly correlated with proteinuria and hypoalbuminemia in the puromycin aminonucleoside and adriamycin rat models of nephrotic syndrome. Notably, in the puromycin aminonucleoside model, hyperfibrinogenemia and antithrombin deficiency were also correlated with proteinuria severity, consistent with reports in human nephrotic syndrome. Importantly, although coagulation was not spontaneously activated in vivo with increasing proteinuria, vascular injury induced a more robust thrombotic response in nephrotic animals. In conclusion, hypercoagulopathy is highly correlated with nephrotic disease severity, but overt thrombosis may require an initiating insult, such as vascular injury. Our results suggest that proteinuria and/or hypoalbuminemia could be developed as clinically meaningful surrogate biomarkers of hypercoagulopathy to identify patients with nephrotic syndrome at highest risk for thrombotic disease and potentially target them for anticoagulant pharmacoprophylaxis.

Global assays of hemostasis

PURPOSE OF REVIEW

There exists an imbalance between our understanding of the physiology of the blood coagulation process and the translation of this understanding into useful assays for clinical application. As technology advances, the capabilities for merging the two areas have become more attainable. Global assays have advanced our understanding of the dynamics of the blood coagulation process beyond end point assays and are at the forefront of implementation in the clinic.

RECENT FINDINGS

We will review recent advances in the main global assays with a focus on thrombin generation that have potential for clinical utility. These assays include direct (thrombogram, whole blood, purified systems) and indirect empirical measures of thrombin generation (thromboelastography) and mechanism-based computational models that use plasma composition data from individuals to generate thrombin generation profiles.

SUMMARY

Empirical thrombin generation assays (direct and indirect) and computational modeling of thrombin generation have greatly advanced our understanding of the hemostatic balance. Implementation of these types of assays and visualization approaches in the clinic will potentially provide a basis for the development of individualized patient care. Advances in both empirical and computational global assays have made the goal of predicting precrisis changes in an individual's hemostatic state one step closer.