Diane J. Nugent

Pathogenesis of chronic immune thrombocytopenia: increased platelet destruction and/or decreased platelet production.

Chronic immune thrombocytopenia (ITP) is a haematological disorder in which patients predominantly develop skin and mucosal bleeding. Early studies suggested ITP was primarily due to immune‐mediated peripheral platelet destruction. However, increasing evidence indicates that an additional component of this disorder is immune‐mediated decreased platelet production that cannot keep pace with platelet destruction. Evidence for increased platelet destruction is thrombocytopenia following ITP plasma infusions in normal subjects, in vitro platelet phagocytosis, and decreased platelet survivals in ITP patients that respond to therapies that prevent in vivo platelet phagocytosis; e.g., intravenous immunoglobulin G, anti‐D, corticosteroids, and splenectomy. The cause of platelet destruction in most ITP patients appears to be autoantibody‐mediated. However, cytotoxic T lymphocyte‐mediated platelet (and possibly megakaryocyte) lysis, may also be important. Studies supporting suppressed platelet production include: reduced platelet turnover in over 80% of ITP patients, morphological evidence of megakaryocyte damage, autoantibody‐induced suppression of in vitro megakaryocytopoiesis, and increased platelet counts in most ITP patients following treatment with thrombopoietin receptor agonists. This review summarizes data that indicates that the pathogenesis of chronic ITP may be due to both immune‐mediated platelet destruction and/or suppressed platelet production. The relative importance of these two mechanisms undoubtedly varies among patients.

Factor XIII deficiency

Summary.  Inherited factor XIII (FXIII) deficiency is a rare bleeding disorder that can present with umbilical bleeding during the neonatal period, delayed soft tissue bruising, mucosal bleeding and life‐threatening intracranial haemorrhage. FXIII deficiency has also been associated with poor wound healing and recurrent miscarriages. FXIII plays an integral role in haemostasis by catalysing the cross‐linking of fibrin, platelet membrane and matrix proteins throughout thrombus formation, thus stabilizing the blood clot. The molecular basis of FXIII deficiency is characterized by a high degree of heterogeneity, which contributes to the different clinical manifestations of the disease. There have been more than 60 FXIII mutations identified in the current literature. In addition, single nucleotide polymorphisms have been described, some of which have been shown to affect FXIII activity, contributing further to the heterogeneity in patient presentation and severity of clinical symptoms. Although there is a lifelong risk of bleeding, the prognosis is excellent when current prophylactic treatment is available using cryoprecipitate or plasma‐derived FXIII concentrate.

Recombinant activated factor VII effectively reverses the anticoagulant effects of heparin, enoxaparin, fondaparinux, argatroban, and bivalirudin ex vivo as measured using thromboelastography.

Bleeding is the major adverse reaction to anticoagulants, leading to significant morbidity and even mortality. Protamine is a specific antidote for heparin yet is only partially effective for enoxaparin, and the activated factor X inhibitor fondaparinux and the direct thrombin inhibitors argatroban and bivalirudin lack specific antidotes. We evaluated the ability of recombinant activated factor VII (rFVIIa), a general hemostatic agent, to reverse the anticoagulant effects of heparin, enoxaparin, fondaparinux, argatroban, and bivalirudin, as measured by thromboelastography. Whole-blood samples containing each test anticoagulant, with or without rFVIIa 1.5–4.5 μg/ml, were prepared ex vivo (n ⩾ 48, each anticoagulant) and analyzed by thromboelastography. The thromboelastography parameters of clot initiation, propagation, rigidity and elasticity were compared for the ex-vivo samples for each anticoagulant. The reversal ability of rFVIIa was also assessed using the standard clinical assay used to monitor each anticoagulant. Thromboelastography was performed on blood from eight stably anticoagulated patients, with and without exogenous rFVIIa. For each anticoagulant, rFVIIa significantly improved and, in some cases, completely normalized all thromboelastography parameters (P < 0.001). rFVIIa significantly (P < 0.01) decreased the activated partial thromboplastin time for argatroban-containing, bivalirudin-containing, or heparin-containing blood yet did not affect the anti-activated factor X levels for enoxaparin-containing or fondaparinux-containing blood. By thromboelastography, rFVIIa exerted generally similar reversal effects on the anticoagulated patient samples as on the ex-vivo samples. In conclusion, rFVIIa effectively reverses the anticoagulant effects of heparin, enoxaparin, fondaparinux, argatroban, and bivalirudin, and should be considered for patients with excessive bleeding associated with these anticoagulants.

Standardization of thromboelastography: A report from the TEG-ROTEM working group

Summary.  Laboratory evaluation of bleeding disorders has been performed with the standard clotting assays such as the PT and PTT for several decades. Our improved understanding of the process of blood coagulation has now revealed the important role played by the cellular elements such as platelets, monocytes and red blood cells. The need for a test that can assess clotting in a more ‘global’ manner, beyond the initiation of clot formation, has led to greater interest in assays such as thrombin generation and thromboelastography. Even though there are several publications using thromboelastography it remains a research tool as the methodology is not standardized. In an attempt to show reproducibility and consistency using thromboelastography, a group of investigators from different countries joined hands to form the TEG‐ROTEM Working Group. Two studies were performed using PRP and FVIII deficient plasma and an intrinsic pathway activator. This article summarizes the results of the first international effort at standardization of thromboelastography. Both of the instruments using this technology (TEG® and ROTEM®) were used. Nine laboratories from countries around the globe participated in this effort. The results showed a significant inter‐laboratory variance with CV’s greater than 10%. Although these results were not satisfactory, this has been the first effort to standardize this methodology and significant work remains to be done to improve reliability and reproducibility. These studies were performed on PRP and the results may be more reliable when preformed on whole blood samples. We believe that it is important to continue this work so that we may investigate the usefulness and potential applications of thromboelastography in the evaluation of bleeding and thrombosis.

Sequential therapy with activated prothrombin complex concentrates and recombinant FVIIa in patients with severe haemophilia and inhibitors: update of our previous experience

Summary.  Haemophilia patients with inhibitors can develop bleeding episodes, which are refractory to monotherapy with either recombinant factor VIIa (rFVIIa) or activated prothrombin complex concentrates (APCC). Management of such bleeds is often difficult. We previously reported the safety of using a combination of rFVIIa and APCC given in sequential fashion. In this report, we update our experience with sequential therapy. A retrospective review of medical records was conducted including all reports of sequential therapy defined as receiving both rFVIIa and APCC within 6 h. Data extracted included demographic data, treatment prior to and following hospital admission, clinical data including type and location of bleed, response to therapy, physical examination and laboratory data. In addition, for some patients, thromboelastography was performed to document the effect of sequential therapy on clot formation characteristics. Four patients comprising 35 admissions, 209 hospital days and 115 days of sequential therapy were included in the updated dataset. No patient developed thrombosis or overt disseminated intravascular coagulation (DIC) although elevations in the D‐dimer above 5 μg mL−1 were noted in 42% of the courses that lasted >3 days. Efficacy is suggested by the fact that patients had resolution of their bleeds after a median of 3 days of sequential therapy after failing to respond to a median of 3 days of monotherapy. Thromboelastography demonstrated an additive effect. Sequential therapy is a safe, potentially efficacious approach in the management of refractory bleeding episodes in patients with haemophilia and inhibitors.

Individualization of bypassing agent treatment for haemophilic patients with inhibitors utilizing thromboelastography

Summary.  The treatment of bleeding for haemophilic patients with inhibitors relies on the use of the bypassing agents, recombinant factor VIIa and factor eight inhibitor bypass activity (FEIBA). While both therapies are effective in the majority of bleeding episodes, there is a significant amount of interindividual variability when it comes to the response to therapy. As of yet, there is no reliable laboratory parameter that can predict the response to therapy in the same manner that factor VIII and factor IX levels predict response in non‐inhibitor patients. Developing such a laboratory parameter is vital in order to maximize the clinical efficacy of these agents. Thromboelastography (TEG) is a device, which assesses clot formation over time in whole blood and has several characteristics which suggest it may be an effective way to monitor bypass agent therapy. We studied the ability of TEG to individualize the treatment regimens of three patients with high titre inhibitors assessing the response to recombinant factor VIIa, FEIBA, and when both were used sequentially. The TEG allowed for individualization of treatment for each of the three patients and resulted in more effective, convenient and less expensive treatment regimens. We thus believe that TEG is a promising device for monitoring of bypass agent therapy and should be studied further.

Neutralizing antibodies against adeno-associated virus examined prospectively in pediatric patients with hemophilia

Recombinant adeno-associated virus (rAAV) is a promising gene delivery vector and has recently been used in patients with hemophilia. One limitation of AAV application is that most humans have experienced wild-type AAV serotype 2 exposure, which frequently generates neutralizing antibodies (NAbs) that may inhibit rAAV2 vector transduction. Employing alternative serotypes of rAAV vectors may circumvent this problem. We investigated the development of NAbs in early childhood by examining sera gathered prospectively from 62 children with hemophilia A, participating in a multi-institutional hemophilia clinical trial (the Joint Outcome Study). Clinical applications in hemophilia therapy have been suggested for serotypes AAV2, AAV5 and AAV8, therefore NAbs against these serotypes were serially assayed over a median follow-up of 4 years. NAbs prevalence increased during early childhood for all serotypes. NAbs against AAV2 (43.5%) were observed more frequently and at higher titers compared with both AAV5 (25.8%) and AAV8 (22.6%). NAbs against AAV5 or AAV8 were rarely observed in the absence of co-prevalent and higher titer AAV2 NAbs, suggesting that NAbs to AAV5 and AAV8 were detected following AAV2 exposure due to partial cross-reactivity of AAV2-directed NAbs. The results may guide rational design of clinical trials using alternative AAV serotypes and suggest that younger patients who are given AAV gene therapy will benefit from the lower prevalence of NAbs.

Sites of initial bleeding episodes, mode of delivery and age of diagnosis in babies with haemophilia diagnosed before the age of 2 years: a report from The Centers for Disease Control and Prevention’s (CDC) Universal Data Collection (UDC) project

Summary.  Lack of detailed natural history and outcomes data for neonates and toddlers with haemophilia hampers the provision of optimal management of the disorder. We report an analysis of prospective data collected from 580 neonates and toddlers aged 0–2 years with haemophilia enrolled in the Universal Data Collection (UDC) surveillance project of the Centers for Disease Control and Prevention (CDC). This study focuses on a cohort of babies with haemophilia whose diagnosis was established before the age of two. The mode of delivery, type and severity of haemophilia, onset and timing of haemorrhages, site(s) of bleeding, provision of prophylaxis with coagulation factor replacement therapy, and the role played by the federally funded Haemophilia Treatment Centers (HTC) in the management of these infants with haemophilia were evaluated. Seventy‐five per cent of haemophilic infants were diagnosed early, in the first month of life, especially those with a family history or whose mothers were known carriers; infants of maternal carriers were more likely to be delivered by C‐section. Involvement of an HTC prior to delivery resulted in avoidance of the use of assisted deliveries with vacuum and forceps. Bleeding from the circumcision site was the most common haemorrhagic complication, followed by intra‐ and extra‐cranial haemorrhages and bleeding from heel stick blood sampling. Eight per cent of the infants were administered factor concentrate within 24 h of birth; more than half were treated to prevent bleeding. This study highlights the significant rate and the sites of initial bleeding unique to very young children with haemophilia and underscores the need for research to identify optimal evidence‐based recommendations for their management.

Prophylactic recombinant factor VIIa in haemophilia patients with inhibitors

Summary.  Prevention of bleeding, especially into joints, with prophylactic factor infusions is the most effective treatment for severe haemophilia patients. Approximately 15–30% of patients with factor VIII deficiency and 3–5% of patients with factor IX deficiency develop neutralizing antibodies (inhibitors) to factor precluding their use. Such patients often have significant bleeding complications including life‐ and limb‐threatening bleeds and severe joint disease. Prophylaxis for such patients is not generally considered because of the fact that the standard (bypassing) agents for such patients are not as effective as natural factor replacement, because of concerns for thrombotic complications and also because of the very high cost of bypassing agents. We treated two patients with high titre inhibitors with prophylactic recombinant factor VIIa (rFVIIa). The first patient was treated as a result of development of a target joint and to reduce the use of agents that can lead to anamnesis of his inhibitor. The second patient had multiple severe bleeds and was hospitalized 20% of the time over a 2‐year period. He had a very poor quality of life. Both patients had shown good responses previously to rFVIIa for treatment of bleeds. Both patients had an outstanding response to prophylaxis albeit at a very high cost. Prophylaxis with rFVIIa can be an effective approach in select inhibitor patients with severe complications related to bleeding.

Sequential therapy with activated prothrombin complex concentrate and recombinant factor VIIa in patients with severe haemophilia and inhibitors

Summary.  Patients with haemophilia and inhibitors have bleeding episodes that can be refractory to home therapy with either activated prothrombin complex concentrate (APCC) or recombinant factor VIIa (rFVIIa). Sequential therapy with these products has not been widely used because of concern regarding the possibility of thrombosis. This report describes the results of a retrospective chart review of five hospitalized children with severe haemophilia and inhibitors who have been treated with sequential doses of APCC and rFVIIa for refractory bleeding. These patients all had failed home therapy with APCC and rFVIIa alone. A total of 20 admissions were documented covering 170 hospital days, including 91 days of combination therapy. While being closely monitored in the hospital, they received alternating doses of APCC and rFVIIa every 6 h. Anywhere from one to three doses of rFVIIa were given every 2 h between APCC doses. Doses of APCC ranged from 35 to 80 U kg−1 dose−1, and doses of rFVIIa ranged from 80 to 225 mcg kg−1 dose−1. There was no clinical or laboratory evidence of thrombosis, thrombocytopenia, or disseminated intravascular coagulation (DIC). We found the combination of these factors to be safe and effective for patients with refractory bleeds. However, we recommend this aggressive therapy only in the inpatient setting with careful monitoring of the physical examination and frequent laboratory screening to assess for thrombosis and DIC, and without the concurrent use of antifibrinolytic medications.