Evaluation of the use of global haemostasis assays to monitor treatment in factor XI deficiency.

INTRODUCTION: Previous guidelines recommend that FXI:C levels should be used to monitor FXI replacement in factor XI (FXI) deficiency. However, FXI:C levels do not correlate with bleeding tendency in this disorder and may not be the optimal test by which to monitor and determine further treatment in the postoperative period. AIM: To assess whether the thrombin generation assay (TGA) and rotational thromboelastometry can be used to monitor FXI replacement peri-operatively in FXI deficiency and to determine if changes in FXI:C levels correlate with changes in thrombin generation and clot formation parameters following treatment with solvent-detergent fresh frozen plasma (SD-FFP). METHODS: The TGA and rotational thromboelastometry were used to measure thrombin generation and clot formation in 11 adults with FXI deficiency who were treated with either SD-FFP (n = 8) or FXI concentrate (n = 3) as prophylaxis peri-operatively. Blood samples were taken pre- and 30 min post-treatment. RESULTS: Global haemostasis assays can be used to measure the effect of FXI replacement with SD-FFP or FXI concentrate in FXI deficiency. Both treatment types improved thrombin generation and clot formation. However, the remaining response to treatment at 24 h post SD-FFP was variable and changes in FXI:C levels were not predictive of changes in thrombin generation/thromboelastometry parameters after treatment with SD-FFP. CONCLUSION: Global haemostasis assays may provide a more reliable means of monitoring SD-FFP treatment with the potential to prevent individuals receiving unnecessary treatment, however, their clinical use in decision making needs to be tested in a larger prospective study.

The Management of Factor XI Deficiency in Pregnancy.

Management of factor XI (FXI) deficiency in pregnancy is complicated by lack of correlation between FXI level and bleeding risk. Clinicians should be vigilant about the potential for prolonged or excessive bleeding following miscarriage or termination of pregnancy, or postpartum hemorrhage (PPH). A multidisciplinary approach along with an individual care plan is recommended to prevent bleeding complications. Assessment of bleeding history, FXI level, and global tests of hemostasis can aid management decisions regarding hemostatic prophylaxis. The risk of PPH can be minimized by obstetric measures to avoid uterine atony and genital trauma, in addition to provision of appropriate hemostatic prophylaxis for labor and delivery. Women with FXI deficiency can be given the option of regional anesthesia, provided that prior consideration has been given to assessment of potential bleeding risk and appropriate treatment strategies are implemented. Antifibrinolytic agents are effective for the majority of women with FXI deficiency, but those with severe deficiency/phenotype require FXI concentrate. Recombinant activated factor VII (rFVIIa) has also been used successfully to prevent bleeding in FXI deficiency. However, all treatments should be used with caution in pregnancy due to thrombogenic potential. Neonatal bleeding complications are rare in FXI deficiency; however, hemostatic assessment and cover are important for invasive procedures such as circumcision.

In vitro comparison of the effect of two factor XI (FXI) concentrates on thrombin generation in major FXI deficiency.

INTRODUCTION: Bleeding risk in factor XI (FXI) deficiency following surgery may be reduced by treatment with either of two FXI concentrates, but indications for their use are unclear and treatment has been associated with thrombosis. AIM: To quantify and compare the effects of two different FXI concentrates on thrombin generation (TG) in major FXI deficiency (FXI:C < 15 IU dL(-1) ). METHODS: Thrombin generation was measured in controls (n = 50), FXI-deficient individuals pre and post in vitro spiking with FXI concentrates (n = 10), and in ex vivo samples following treatment with FXI concentrate (n = 3). RESULTS: Thrombin generation was significantly impaired in FXI deficiency but improved following FXI replacement in vitro and in vivo. LFB Hemoleven(®) had greater effect on TG than BPL FXI concentrate in vitro (equivalent in vivo doses 10, 20 and 30 U kg(-1) ): higher endogenous thrombin potential (ETP) (P < 0.0001), peak height (P < 0.01) velocity (P < 0.0002) and shorter lag time and time to peak (both P < 0.003). Some measurements with LFB Hemoleven(®) exceeded the reference range. At lower dose (5 U kg(-1) ), BPL FXI concentrate normalized all TG parameters and LFB Hemoleven(®) normalized the ETP but exceeded the reference range with other parameters. CONCLUSION: Both FXI concentrates improve TG in vitro in major FXI deficiency but differ in dose response, and for both products, doses lower than previously recommended normalized TG in vitro. Comparison of in vitro spiked and ex vivo samples suggest that in vitro results could be used to estimate an expected in vivo response to FXI replacement.

Safety and efficacy of factor XI (FXI) concentrate use in patients with FXI deficiency: a single-centre experience of 19 years.

AIM: Factor XI (FXI) concentrate is a pooled human plasma-derived factor concentrate used as replacement therapy for patients with FXI deficiency, which provides a predictable response and consistent haemostatic cover in emergency or elective situations. It has previously been implicated in adverse events such as thrombosis and inhibitor formation, with rare case reports of fatal incidents. We sought to establish the incidence of such complications in a retrospective case series between 1994 and 2012 at the Haemophilia Comprehensive Care Centre at Royal Free Hospital, London, UK. METHODS: Patients who received FXI concentrate had their medical records reviewed to extract information and specific adverse events recorded such as failure of treatment with further bleeding, suspected viral transfusion transmitted infection (TTI), thrombosis or inhibitor formation. RESULTS: Eighty-six patients received 242 treatment episodes of FXI concentrate. Ninety percent of treatment episodes were covered with BPL FXI concentrate and 10% with LFB Hemoleven. Twelve (5%) adverse events were recorded, with eight (3.3%) of all treatment episodes were related to persistent bleeding postconcentrate infusion and there were 4 (1.7%) non-bleeding adverse events. No viral TTIs were identified. There were two recorded inhibitors, one thrombotic event (central retinal artery occlusion) and one transfusion reaction. No patient suffering an adverse event resulted in long-term morbidity. CONCLUSION: Our experience of FXI concentrate use demonstrates infrequent minor adverse events related to its administration and is a safe product to use.

Ongoing risk of thrombosis with factor XI concentrate: 5 years experience in two centres.

INTRODUCTION: Factor XI (FXI) deficiency is the commonest of the rare bleeding disorders, affecting 2079 individuals in the United Kingdom. Treatment options for bleeding or surgery include antifibrinolytics, fresh frozen plasma or plasma-derived (pd) FXI concentrates. There were a number of reports of thrombosis following treatment with FXI concentrates prior to changes in their manufacturing processes made in the mid-1990's. AIMS: The aim of the study was to determine the occurrence of adverse events (haemorrhagic and thrombotic) following usage of pd-FXI concentrates at two large UK haemophilia centres. Retrospective chart review of all consecutively treated patients with BPL Factor XI(®) or Hemoleven(®) over a 5-year period (11/06-11/11) was performed. RESULTS: Twenty-nine patients (median age = 57.1 years) received treatment over 64 treatment episodes (surgery = 56, bleeding = 5, other = 3), using 126 000 U of concentrate. Median baseline FXI:C was 9 U dL(-1) (range = <1-51), with 21 having severe and eight partial deficiency. BPL Factor XI(®) was used in 39 episodes (79 110 U) and Hemoleven(®) 25 episodes (46 890 U). There were six clinically significant bleeding events, managed either with a single additional dose of FXI concentrate (n = 4) or requiring no further intervention (n = 2). One patient required blood transfusion and one oral iron replacement. Two thrombotic events (transient ischaemic attack and pulmonary emboli), occurred in two patients with severe FXI deficiency, despite cautious FXI concentrate usage in the perioperative period. CONCLUSIONS: FXI concentrate use is efficacious and safe in the majority of cases although physicians should remain mindful of the possibility of thrombotic complications.

Bleeding phenotype and correlation with factor XI (FXI) activity in congenital FXI deficiency: results of a retrospective study from a single centre.

Bleeding phenotype in factor XI (FXI)-deficient patients is variable, and not related to baseline FXI:Act. Aims of our study were to describe the characteristics and the management of surgery and deliveries in FXI-deficient patients, and to investigate the relationship between the haemorrhagic phenotype and the baseline FXI:Act. Ninety-five patients were diagnosed and followed in our centre for a median follow-up of 0.9 years (0.1-36.2); median FXI:Act of all patients: 38% (0.5-69%). Fifty-six patients (59%) experienced bleeding episodes not surgery-related. Prior to diagnosis, 64 patients underwent 132 surgeries, and after diagnosis, 23 patients underwent 36 surgeries. Globally 26 of 168 surgeries were prophylactically treated, whereas 142 of 168 were not. As regard as surgeries performed without prophylaxis, 30 bleeding events (21%) occurred in 21 patients. At diagnosis, the median FXI:Act of bleeding and non-bleeding patients was 28% and 37%, respectively, without statistically significant difference between the two groups (P = 0.26). As regard as surgeries performed under prophylactic treatment just 1 bleeding event occurred. Prior to diagnosis, 31 spontaneous deliveries (SD) and eight caesarian sections (CS) were performed without prophylaxis: 4 postpartum haemorrhages (10.5%) occurred (patients FXI:Act: 2%, 6%, 27%, 52.3% respectively). After diagnosis, four SD and five CS were performed with prophylaxis: no postpartum haemorrhages occurred. We confirm the wide bleeding phenotype variability in FXI-deficient patients, not related to the baseline FXI:Act levels. We highlight the importance of performing a correct diagnosis and follow-up, because a good management of prophylactic treatment, dramatically reduces the bleeding rate in case of surgery or deliveries.

Factor XI replacement for inherited factor XI deficiency in routine clinical practice: results of the HEMOLEVEN prospective 3-year postmarketing study.

Factor XI (FXI)-deficient patients may develop excessive bleeding after trauma or surgery. Replacement therapy should be considered in high-risk situations, especially when FXI levels are below 20 IU dL(-1) . HEMOLEVEN is a human plasma-derived factor XI concentrate available in France since 1992, but there are few data regarding its use by physicians. This prospective study assessed the use, efficacy and safety of HEMOLEVEN in common clinical practice. HEMOLEVEN was evaluated in FXI-deficient patients in 13 French centres in a 3-year postmarketing study. Forty-four patients (30 females, 14 males) received 67 treatments. The median age was 37 years (8 months-91 years). Basal FXI levels were <1 to 51 IU dL(-1) (median: 5.5); 29 patients were severely FXI-deficient (<20 IU dL(-1) ). FXI was administered prophylactically before 43 surgical procedures, 10 invasive procedures, 8 vaginal deliveries, or as curative treatment for six bleeds. The efficacy was assessed as excellent/good in 63, moderate in two and undetermined in two treatments. Seven patients experienced seven adverse effects, including two rated as serious: one sudden massive pulmonary embolism with fatal outcome and one case of inhibitor to FXI. HEMOLEVEN is effective for bleeding prevention in FXI deficiency. However, considering the benefit/risk ratio observed in relation to dosage in this study; firstly, it should be used sparingly due to its potential prothrombotic effect; secondly, new prescription procedures should be defined to adapt the dosage, especially in patients with intrinsic and/or acquired risk factors for thrombosis.

Factor XI and coagulation. Factor XI inhibitors - antithrombotic perspectives.

Factor XI is a zymogen with an important role in the coagulation cascade. It is activated by FXII, thrombin and or it can be autoactivated. It has a prothrombotic effect after being activated by thrombin, but also through its antifibrinolytic action, stabilizing the formed clot. Hereditary deficiency of FXI causes haemophilia C - a disease manifested by an usually provoked, small to moderate mucosal bleeding. People with severe FXI deficiency have a low risk of thrombotic events. Conversely, increased FXI values have been found to be associated with increased risk of venous thromboembolism and ischemic stroke. Lowering serum FXI levels has become a treatment target for the prevention of thrombotic events. New pharmacological agents - FXI inhibitors - have been investigated in phase II clinical trials, with promising results in terms of efficacy and safety in the prevention of thrombotic events. FXI inhibitors are emerging as new anticoagulant agents with broad indication prospects beyond direct oral anticoagulants and vitamin K antagonists.

Targeting coagulation factor XII provides protection from pathological thrombosis in cerebral ischemia without interfering with hemostasis.

Formation of fibrin is critical for limiting blood loss at a site of blood vessel injury (hemostasis), but may also contribute to vascular thrombosis. Hereditary deficiency of factor XII (FXII), the protease that triggers the intrinsic pathway of coagulation in vitro, is not associated with spontaneous or excessive injury-related bleeding, indicating FXII is not required for hemostasis. We demonstrate that deficiency or inhibition of FXII protects mice from ischemic brain injury. After transient middle cerebral artery occlusion, the volume of infarcted brain in FXII-deficient and FXII inhibitor-treated mice was substantially less than in wild-type controls, without an increase in infarct-associated hemorrhage. Targeting FXII reduced fibrin formation in ischemic vessels, and reconstitution of FXII-deficient mice with human FXII restored fibrin deposition. Mice deficient in the FXII substrate factor XI were similarly protected from vessel-occluding fibrin formation, suggesting that FXII contributes to pathologic clotting through the intrinsic pathway. These data demonstrate that some processes involved in pathologic thrombus formation are distinct from those required for normal hemostasis. As FXII appears to be instrumental in pathologic fibrin formation but dispensable for hemostasis, FXII inhibition may offer a selective and safe strategy for preventing stroke and other thromboembolic diseases.

Are hemostasis and thrombosis two sides of the same coin?

Factor XII (FXII), a clotting enzyme that can initiate coagulation in vitro, has long been considered dispensable for normal blood clotting in vivo because hereditary deficiencies in FXII are not associated with spontaneous or excessive bleeding. However, new studies show that mice lacking FXII are protected against arterial thrombosis (obstructive clot formation) and stroke. Thus, FXII could be a unique drug target that could be blocked to prevent thrombosis without the side effect of increased bleeding.

Rare bleeding disorders.

Rare bleeding disorders (RBDs) include the inherited deficiencies of fibrinogen, factor (F)II, FV, FV+FVIII, FVII, FX, FXI and FXIII. There have been remarkable advances in understanding the molecular profiles that lead to each type of coagulation factor deficiency. However, as a consequence of their rarity, clinical data regarding the characteristics of bleeding symptoms and their management remain limited. The clinical manifestations in different RBDs are heterogeneous, and the residual plasma coagulant factor level does not always predict bleeding tendency. In this review, we describe the general features and recent advances in understanding three such deficiencies: FXI, FVII and fibrinogen deficiencies.

Factor XI and XII as antithrombotic targets.

PURPOSE OF REVIEW: Arterial and venous thrombosis are major causes of morbidity and mortality, and the incidence of thromboembolic diseases increases as a population ages. Thrombi are formed by activated platelets and fibrin. The latter is a product of the plasma coagulation system. Currently available anticoagulants such as heparins, vitamin K antagonists and inhibitors of thrombin or factor Xa target enzymes of the coagulation cascade that are critical for fibrin formation. However, fibrin is also necessary for terminating blood loss at sites of vascular injury. As a result, anticoagulants currently in clinical use increase the risk of bleeding, partially offsetting the benefits of reduced thrombosis. This review focuses on new targets for anticoagulation that are associated with minimal or no therapy-associated increased bleeding. RECENT FINDINGS: Data from experimental models using mice and clinical studies of patients with hereditary deficiencies of coagulation factors XI or XII have shown that both of these clotting factors are important for thrombosis, while having minor or no apparent roles in processes that terminate blood loss (hemostasis). SUMMARY: Hereditary deficiency of factor XII (Hageman factor) or factor XI, plasma proteases that initiate the intrinsic pathway of coagulation, impairs thrombus formation and provides protection from vascular occlusive events, while having a minimal impact on hemostasis. As the factor XII-factor XI pathway contributes to thrombus formation to a greater extent than to normal hemostasis, pharmacological inhibition of these coagulation factors may offer the exciting possibility of anticoagulation therapies with minimal or no bleeding risk.

A proposal for managing bleeding in patients on therapeutic factor XI(a) inhibitors.

Several drugs that reduce functional levels of the plasma protease zymogen factor XI (FXI), or that inhibit its activated form (FXIa), are being evaluated as treatments to prevent thrombosis. Based on the observation that individuals with inherited FXI deficiency have a relatively mild bleeding disorder, it is anticipated that therapeutic FXI(a) inhibitors will have a smaller impact on hemostasis than anticoagulants targeting thrombin or factor Xa. However, even if FXI(a) inhibitors are determined to be safer than currently used anticoagulants, some patients on these drugs will experience abnormal bleeding or require emergent surgery. Strategies for dealing with such situations are required. Treatment with antifibrinolytic agents and low doses of recombinant factor VIIa effectively prevent abnormal bleeding in FXI-deficient patients with alloantibody inhibitors to FXI who undergo surgery. We propose that a similar strategy can be used for patients on therapeutic FXI(a) inhibitors who are bleeding or require invasive procedures.

The role of recombinant factor VIIa for obstetric block in women with severe factor XI deficiency.

Regional blocks like spinal, epidural and combined spinal epidural (CSE) are relatively contraindicated in individuals with bleeding disorders. Consequently pregnant women with severe factor XI (FXI) deficiency are often denied this option during labour and caesarean section. We describe three women with severe FXI deficiency in whom regional block was performed with low-dose recombinant factor VIIa (rFVIIa) for their operative procedures during delivery. All women achieved haemostasis and had uncomplicated regional block, delivery and surgical procedures. The point of care device--rotational thromboelastometry (ROTEM) was used to monitor the patients' coagulation and determine the dose of rFVIIa to achieve in vitro haemostasis in these women that was then subsequently used in vivo. Low-dose rFVIIa seems to be effective and safe in the management of delivery and enables provision of regional blocks in women with severe FXI deficiency.

Successful hip arthroplasty in an adult male with severe factor XI deficiency using Hemoleven®, a factor XI concentrate.

Severe factor XI (sFXI) deficiency is a rare bleeding disorder (RBD). FXI replacement is most often required for surgical hemostasis. Plasma, the sole US treatment option, is often complicated by life-threatening allergic reactions. In such circumstances, the FDA offers a mechanism for institution-industry collaboration to facilitate limited use of replacement products licensed abroad. A 58 years old man with sFXI deficiency, required hip replacement. In the past, he received prophylactic plasma for thyroidectomy and experienced a severe allergic reaction. A single use institutional IND FDA application was initiated in collaboration with LFB (Les Ulis, France) to access Hemoleven®, a plasma-derived FXI concentrate. The application required an investigator-initiated IRB-approved protocol for treatment and safety/efficacy monitoring that included: preoperative thrombophilia, FXI inhibitor and pharmacokinetic (PK) evaluations; peri- postoperative administration of ≤ 4 doses of 10-15 U/kg Hemoleven® ; DIC monitoring; postoperative thromboprophylaxis; observation for product efficacy and potential complications. PK study demonstrated the expected 1.8% FXI recovery per U/kg with half-life of 62 hours. Mild D-Dimer elevation was noted 6-9 hours post-infusion. The initial dose (15 U/kg) was administered 15 hours before surgery; subsequently, 3 doses (10 U/kg) were infused every 72 hours. Hemostasis was excellent. No complications were observed. Collaboration allowed for successful patient access to Hemoleven® with excellent PK, safety, and efficacy. This case underscores the need for additional efforts to ensure safe and effective licensed replacement therapies for RBD patients.

[Long-term response to rituximab in a patient with acquired hemophilia]. / Respuesta a largo plazo con rituximab en una paciente con hemofilia adquirida.

A 28 year-old female without history of previous disease. In the seventh month of her first pregnancy she developed hemorrhagic tendency that worsened in the early postpartum period. Activated partial thromboplastin time was 110 sec (control=35.8 sec) with negative tests for lupus anticoagulant. Factor VIII was <1% and a factor VIII inhibitor titer was 84 Bethesda Units/mL (BU). Initial therapy included methylprednisolone, prednisone, and cyclophosphamide. After two weeks of treatment, clinical conditions of the patient improved slightly and she was discharged. Outpatient therapy included azathioprine, and prednisone for a period of 22 months but in-hospital management was several times required. We initiated rituximab 375 mg/m2/week/4 weeks. A clinical improvement and increased levels of factors VIII and XI were observed 10 weeks later and factor VIII inhibitor decreased to undetectable levels. After a 82-month follow-up period (since the first rituximab infusion), she is asymptomatic and factor VIII and factor XI plasma levels are 70% and 94%, respectively FVIII inhibitor level is still undetectable. Rituximab seems an alternative for the treatment of acquired hemophilia refractory to standard treatment.

Anticoagulant therapy in patients with congenital FXI deficiency.

The bleeding phenotype of factor XI (FXI) deficiency is unpredictable. Bleeding is usually mild and mostly occurs after injury. Although FXI deficiency renders antithrombotic protection, some patients might eventually develop thrombosis or atrial fibrillation, requiring anticoagulant therapy. There is almost no evidence on the bleeding risk in this scenario. Our retrospective study of 269 white FXI-deficient subjects (1995-2021) identified 15 cases requiring anticoagulation. They harbored 8 different F11 variants, mainly in heterozygosis (1 case was homozygote), and had mild to moderate deficiency (FXI:C: 20% to 70%). Two subjects (13.3%) had bleeding history before anticoagulation. Atrial fibrillation was the main indication (12/15; 80%). Fourteen patients started therapy with vitamin K antagonists (VKA), but 4 subjects were on direct oral anticoagulants (DOACs) at the end of follow-up. Over >1000 months of anticoagulation, 2 mild bleeding episodes in 2 patients (13.3%, 95% confidence interval: 3.7% to 37.9%) were recorded. No major/fatal events were reported. "Pre-post" bleeding localization and severity did not change despite treatment. On VKA, drug dosing and management were also standard, unaltered by FXI deficiency. We provide the largest description of anticoagulant use in FXI deficiency, and the first cases receiving DOACs. Although further studies are needed, our observations suggest that moderate FXI deficiency does not interfere with anticoagulant management nor bleeding risk.