The diagnosis and management of factor VIII and IX inhibitors: a guideline from the United Kingdom Haemophilia Centre Doctors Organisation

Activated prothrombin complex concentrate (FEIBA®) for the treatment and prevention of bleeding in patients with acquired haemophilia: A sequential study

Despite anti-haemorrhagic therapy with proper doses of activated prothrombin complex concentrate (aPCC, Feiba®), patients with acquired haemophilia A (AHA) have a considerable risk of recurrent bleeding complications. Evidence in support of the benefit-to-risk ratio of prevention strategies with the use of lower doses of aPCC following the end of the initial treatment period is scarce and inconclusive. We report our experience in the management of 18 consecutive patients with AHA admitted to two Haemophilia centres in Italy. We managed the first 11 according to current guidelines (e.g., with conventional aPCC doses until bleeding resolution). Then, we decided to prolong the treatment beyond bleeding resolution with lower doses of the same concentrate (short-term prophylaxis) in the 7 additional patients. In these patients, the treatment was continued for as long as the titre of FVIII inhibitor was found to decrease by at least 50% when compared to the baseline one. We observed six relapses of bleeding in patients in whom aPCC was confined to the treatment of the qualifying bleeding episode, and none in patients to whom lower doses were administered until the pre-specified decrease in the titre of FVIII inhibitor was achieved. No patients experienced thrombotic complications during the study period. Prolonging the treatment with lower doses of aPCC beyond the initial phase in patients with AHA in whom the titre of FVIII inhibitor is still high is likely to safely prevent further bleeding complications.

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

BACKGROUND

Hemophilia A (HA) is a congenital bleeding disorder resulting from factor VIII deficiency. The most serious complication of HA management is the appearance of inhibitory antibodies (Abs) against injected FVIII concentrates. To eradicate inhibitors, immune tolerance induction (ITI) is usually attempted, but it fails in up to 30% of cases. Currently, no undisputed predictive marker of ITI outcome is available to facilitate the clinical decision.

OBJECTIVES

To identify predictive markers of ITI efficacy.

METHODS

The isotypic and epitopic repertoires of inhibitory Abs were analyzed in plasma samples collected before ITI initiation from 15 children with severe HA and high-titer inhibitors, and their levels were compared in the two outcome groups (ITI success [n = 7] and ITI failure [n = 8]). The predictive value of these candidate biomarkers and of the currently used indicators (inhibitor titer and age at ITI initiation, highest inhibitor titer before ITI, and interval between inhibitor diagnosis and ITI initiation) was then compared by statistical analysis (Wilcoxon test and receiver receiver operating characteristic [ROC] curve analysis).

RESULTS

Whereas current indicators seemed to fail in discriminating patients in the two outcome groups (ITI success or failure), anti-A1 and anti-A2 Ab levels before ITI initiation appeared to be good potential predictive markers of ITI outcome (P < 0.018). ROC analysis showed that anti-A1 and anti-A2 Abs were the best at discriminating between outcome groups (area under the ROC curve of > 0.875).

CONCLUSION

Anti-A1 and anti-A2 Abs could represent new promising tools for the development of ITI outcome prediction tests for children with severe HA.

Induction of immune tolerance to RBC, platelet, and neutrophil antigens and IgA

Antibodies to red blood cell (RBC), platelet, and neutrophil antigens, and IgA may cause serious clinical problems. With a few exceptions, preventing these conditions is a matter of limiting exposure to the foreign antigen while treatment consists of managing the consequences. Might immune tolerance induction (ITI) be possible and beneficial in these situations? Neonatal exposure to antigens is known to induce central tolerance. However central tolerance may not be absolute. Factors that determine whether an antibody will be produced in response to an antigen are not well understood but include the appropriate expression of major histocompatibility complex-class II and/or co-stimulatory molecules on dendritic cells, the presence or absence of adjuvants and whether or not the antigen is presented together with agonists for the toll-like receptor. Modifying these may prevent alloimmunization. Peripheral tolerance, in sensitized individuals, as routinely used in patients with allergic/anaphylactic reactions, those with haemophilia A or B with inhibitors and acquired haemophilia, may also be possible. Briefly, monitored, graded, increasing exposure to the antigen of interest with or without additional immunosuppression is used. Neither central nor peripheral ITI has been tried or suggested for individuals sensitizable or sensitised to RBC, platelet, and neutrophil antigens, or IgA. Theoretically, this is possible and may be of benefit.

Combination of FVIII and low-dose rFVIIa improves haemostasis in acquired haemophilia A patients: a collaborative controlled study

INTRODUCTION

Acquired haemophilia A (AHA) is an autoimmune disease that potentially leads to severe bleeding and has a high rate of mortality. This collaborative study aimed to assess the efficacy of the co-administration of FVIII and low-dose rFVIIa in patients with AHA.

MATERIALS AND METHODS

This study retrospectively compared the combined FVIII/low-dose rFVIIa therapy (initial dose range of 25-55μg/Kg) with the combined FVIII/PCC therapy and low-dose rFVIIa monotherapy. Adverse drug reactions and recurrent bleeding episodes were also monitored. Crude comparisons and the exact conditional logistic regression were performed to compare the outcomes between three treatment groups.

RESULTS

First bleeding episodes of 56 consecutive patients from 5 centres were analyzed, and 37 bleeding episodes (66.1%) were determined to be severe. Specifically, the rate of bleeding control was significantly higher with the FVIII/low-dose rFVIIa therapy compared to that of the low-dose rFVIIa alone therapy or the FVIII/PCC therapy (58.3% vs. 41.7% vs. 95.0%, respectively). Analyzing of total 236 bleeding episodes showed a clear positive association between the early initiation of haemostatic treatment and efficacy. No therapy-related adverse events in which thrombosis predominated were reported.

CONCLUSIONS

The combination of FVIII and low-dose rFVIIa offers an ideal haemostatic cover and may be promoted as a feasible and safe therapy protocol for patients with AHA.

Prolonged Activated Partial Thromboplastin Time

To review the diagnostic difficulties of a prolonged activated partial thromboplastin time (aPTT) when 2 inhibitors with opposite clinical presentations coexist, we searched MEDLINE from January 1970 to November 2013 using acquired, factor VIII (FVIII), factor IX, hemophilia A and B, inhibitor, lupus anticoagulant (LA), antiphospholipid, anticardiolipin, anti-β2-glycoprotein I, antibodies, syndrome, bleeding, and thrombosis. We identified 13 articles for a total of 15 cases of possible coexistence of FVIII inhibitor and LA. The presenting clinical manifestation was thrombosis in 6 cases and bleeding in 9 cases. Activated partial thromboplastin time was the presenting laboratory abnormality in all cases, and first-line investigations suggested the coexistence of LA and acquired FVIII inhibitor. None of the articles addressed the diagnostic accuracy of the screening tests by performing “second line” assays. We reviewed the diagnostic pitfalls of the cases under study and provide some guidance for alternative tests when facing a prolonged aPTT that may have a double meaning.

Inhibitors in haemophilia: what have we learned from registries? A systematic review

Congenital haemophilia A and B are genetic disorders affecting factor VIII and factor IX production, respectively. Factor replacement is the only effective treatment for these deficiencies, but a patient's immune system can develop inhibitory antibodies which bind and interfere with the function of the replaced factor in a variety of ways. The main treatment goal for patients with inhibitors is to induce immune tolerance to the injected factor. If not successful, a different treatment termed bypass therapy is needed to treat bleeds. The goal of this review is to demonstrate the usefulness of haemophilia registries as information sources to supplement available evidence regarding predictors of inhibitor development and immune tolerance induction (ITI) outcomes. In this systematic review, relevant keywords were used to search online academic databases during February 2014. Inclusion criteria were original publication and data obtained from a haemophilia or ITI registry with a minimum of 30 patients. A data collection form was created to extract information from selected manuscripts. Titles, abstracts and then full texts were screened to determine the eligibility of reports for this review. Eleven manuscripts from nine registries were determined eligible and included in the study. Registries have reported on some core variables, but are inconsistent in reporting less practiced predicting variables. Variables that may affect inhibitor and ITI outcomes were each divided into two categories: patient characteristics (such as age and family history) and treatment-related variables (including exposure days, treatment duration and dose). It is recommended that, in addition to exploratory hypothesis testing, a minimum set of variables should be collected and reported by registries. International collaboration and well-designed prospective registries are of major importance to advance this field in order to determine inhibitor risks and ITI outcomes and facilitate the development of new treatments.

Acquired hemophilia: a case report and review of the literature

Acquired hemophilia A (AHA) is a rare bleeding disorder caused by autoantibodies against clotting factor VIII (FVIII). FVIII autoantibody is characterized as polyclonal immunoglobulin G directed against the FVIII procoagulant activity. This disease occurs most commonly in the elderly population and with preponderance of men in nonpregnancy-related AHA. There are well-established clinical associations with AHA such as malignancy, other autoimmune diseases and pregnancy. However, up to 50% of reported cases remain idiopathic. The clinical manifestation of AHA includes mostly spontaneous hemorrhages into skin, muscles and soft tissues, or mucous membranes. AHA should be suspected when a patient with no previous history of bleeding presents with bleeding and an unexplained prolonged activated partial thromboplastin time. The diagnosis is confirmed in the laboratory by the subsequent identification of reduced FVIII levels and FVIII inhibitor titration. There is a high mortality, making prompt diagnosis and treatment vitally important. The principles of treatment consist in controlling the bleeding and eradicating the inhibitor. Because of the overall high relapse rate (15-33%), it is also recommended to follow up these patients. The review summarizes what is currently known about the epidemiology, pathogenesis, clinical features, diagnosis, treatment and prognosis of AHA and starts with a case report.

A Comparison of Efficacy Between Recombinant Activated Factor VII (Aryoseven) and Novoseven in Patients With Hereditary FVIII Deficiency With Inhibitor

Introduction:

This study compared the efficacy of Aryoseven with Novoseven to control bleeding episodes in patients with hemophilia A with inhibitors.

Methods:

Sixty-six patients were randomized into 2 groups, with 4 consecutive block randomization. These groups received Aryoseven and Novoseven dosages of 90 to 120 μg/kg intravenously every 2 hours.

Results:

Median (interquartile range) level of factor VIII (FVIII) inhibitor in groups A and B was 15.0 and 19.0 Bethesda Unit (BU) preadministration. Bleeding onset in group A was 1246 ± 1104 minutes and in group B was 2301 ± 1693 minutes ( P = .311). The Kavakli global response scores and treatment success rate was comparable in both the groups. The side effects in groups A (9.7%) and B (2.9%) were comparable.

Conclusion:

Biosimilar recombinant activated FVII is found to be as effective as Novoseven in the treatment of acute joint bleeding in patients with hemophilia with inhibitors. Its usage will decrease the gaps in hemophilia.

Factor VIII brand and the incidence of factor VIII inhibitors in previously untreated UK children with severe hemophilia A, 2000-2011

The effect of recombinant factor VIII (rFVIII) brand on inhibitor development was investigated in all 407 severe hemophilia A previously untreated patients born in the United Kingdom (UK) between 1 January 2000 and 31 December 2011. Eighty-eight (22%) had been in the RODIN study. Information was extracted from the National Haemophilia Database. Because exposure days (EDs) were not known for some patients, time from first treatment was used as a surrogate for rFVIII exposure. An inhibitor developed in 118 (29%) patients, 60 high and 58 low titer, after a median (interquartile range) of 7.8 (3.3-13.5) months from first exposure and 16 (9-30) EDs. Of 128 patients treated with Kogenate Bayer/Helixate NexGen, 45 (35.2%, 95% confidence interval [CI] 27.4-43.8) developed an inhibitor compared with 42/172 (24.4%, 95% CI 18.6% to 31.4%) with Advate (P = .04). The adjusted hazard ratio (HR) (95% CI) for Kogenate Bayer/Helixate NexGen compared with Advate was 2.14 (1.12-4.10) (P = .02) for high titer and 1.75 (1.11-2.76) (P = .02) for all inhibitors. When excluding UK-RODIN patients, the adjusted HR (95% CI) for high-titer inhibitors was 2.00 (0.93-4.34) (P = .08). ReFacto AF was associated with a higher incidence of all, but not high-titer, inhibitors than Advate. These results will help inform debate around the relative immunogenicity and use of rFVIII brands.

Interventions for treating acute bleeding episodes in people with acquired hemophilia A

BACKGROUND

Acquired hemophilia A is a rare bleeding disorder caused by autoantibodies to coagulation factor VIII (FVIII). In most cases, bleeding episodes are spontaneous and severe at presentation. The optimal hemostatic therapy is controversial.

OBJECTIVES

To determine the efficacy of hemostatic therapies for acute bleeds in people with acquired hemophilia A; and to compare different forms of therapy for these bleeds.

SEARCH METHODS

We searched the Cochrane Central Register of Controlled Trials (CENTRAL) (The Cochrane Library 2014, Issue 4) and MEDLINE (Ovid) (1948 to 30 April 2014). We searched the conference proceedings of the: American Society of Hematology; European Hematology Association; International Society on Thrombosis and Haemostasis (ISTH); and the European Association for Haemophilia and Allied Disorders (EAHAD) (from 2000 to 30 April 2014). In addition to this we searched clinical trials registers.

SELECTION CRITERIA

All randomised controlled trials and quasi-randomised trials of hemostatic therapies for people with acquired hemophilia A, with no restrictions on gender, age or ethnicity.

DATA COLLECTION AND ANALYSIS

No trials matching the selection criteria were eligible for inclusion.

MAIN RESULTS

No trials matching the selection criteria were eligible for inclusion.

AUTHORS' CONCLUSIONS

No randomised clinical trials of hemostatic therapies for acquired hemophilia A were found. Thus, we are not able to draw any conclusions or make any recommendations on the optimal hemostatic therapies for acquired hemophilia A based on the highest quality of evidence. GIven that carrying out randomized controlled trials in this field is a complex task, the authors suggest that, while planning randomised controlled trials in which patients can be enrolled, clinicians treating the disease continue to base their choices on alternative, lower quality sources of evidence, which hopefully, in the future, will also be appraised and incorporated in a Cochrane Review.

National surveillance for hemophilia inhibitors in the United States: Summary report of an expert meeting

On March 12, 2012, the Centers for Disease Control and Prevention (CDC) held a meeting of its partners in hemophilia treatment, community-based organizations, industry, and government to review data and discuss implementation issues relevant to planned United States (U.S.) national inhibitor surveillance. Issues discussed included the current status of inhibitor surveillance in the United Kingdom (UK) and the US, the results of a US inhibitor surveillance feasibility study, proposed national surveillance schemes, laboratory testing and reporting issues and potential opportunities for future inhibitor-related research. It was concluded that implementation of a national program of inhibitor surveillance using standardized testing through an established public health registry along with patient and care provider education and targeted research provide the best opportunity to inform efforts to develop and evaluate effective prevention strategies.

Acquired hemophilia A: a frequently overlooked autoimmune hemorrhagic disorder

Acquired hemophilia A (AHA) is a rare hemorrhagic disease in which autoantibodies against coagulation factor VIII- (FVIII-) neutralizing antibodies (inhibitors) impair the intrinsic coagulation system. As the inhibitors developed in AHA are autoantibodies, the disease may have an autoimmune cause and is often associated with autoimmune disease. Although acute hemorrhage associated with AHA may be fatal and is costly to treat, AHA is often unrecognized or misdiagnosed. AHA should thus be considered in the differential diagnosis particularly in postpartum women and the elderly with bleeding tendency or prolonged activated partial thromboplastin time. Cross-mixing tests and measurement of FVIII-binding antibodies are useful to confirm AHA diagnosis. For treatment of acute hemorrhage, hemostatic therapy with bypassing agents should be provided. Unlike in congenital hemophilia A with inhibitors, in which immune tolerance induction therapy using repetitive infusions of high-dose FVIII concentrates is effective for inhibitor eradication, immune tolerance induction therapy has shown poor efficacy in treating AHA. Immunosuppressive treatment should thus be initiated to eradicate inhibitors as soon as the diagnosis of AHA is confirmed.

Inherited abnormalities of coagulation: hemophilia, von Willebrand disease, and beyond

Bleeding disorders are broadly classified into primary and secondary hemostatic defects. Primary hemostatic disorders (disorders of platelets and von Willebrand factor) mainly result in mucocutaneous bleeding symptoms such as epistaxis, menorrhagia, petechiae, easy bruising, and bleeding after dental and surgical interventions. Secondary hemostatic disorders (congenital or acquired deficiencies of coagulation factors) typically manifest with delayed, deep bleeding into muscles and joints. This article provides a generalized overview of the pathophysiology, clinical manifestations, laboratory abnormalities, and molecular basis of inherited abnormalities of coagulation with a focus on hemophilia, von Willebrand disease, and rare inherited coagulation disorders.

Platelet gene therapy corrects the hemophilic phenotype in immunocompromised hemophilia A mice transplanted with genetically manipulated human cord blood stem cells

Our previous studies have demonstrated that platelet FVIII (2bF8) gene therapy can improve hemostasis in hemophilia A mice, even in the presence of inhibitory antibodies, but none of our studies has targeted human cells. Here, we evaluated the feasibility for lentivirus (LV)-mediated human platelet gene therapy of hemophilia A. Human platelet FVIII expression was introduced by 2bF8LV-mediated transduction of human cord blood (hCB) CD34(+) cells followed by xenotransplantation into immunocompromised NSG mice or NSG mice in an FVIII(null) background (NSGF8KO). Platelet FVIII was detected in all recipients that received 2bF8LV-transduced hCB cells as long as human platelet chimerism persisted. All NSGF8KO recipients (n = 7) that received 2bF8LV-transduced hCB cells survived tail clipping if animals had greater than 2% of platelets derived from 2bF8LV-transduced hCB cells, whereas 5 of 7 survived when human platelets were 0.3% to 2%. Whole blood clotting time analysis confirmed that hemostasis was improved in NSGF8KO mice that received 2bF8LV-transduced hCB cells. We demonstrate, for the first time, the feasibility of 2bF8LV gene delivery to human hematopoietic stem cells to introduce FVIII expression in human platelets and that human platelet-derived FVIII can improve hemostasis in hemophilia A.

Unexpected hemorrhage: an unusual and potentially catastrophic clinical challenge

PURPOSE

Unexpected bleeding or hemorrhage related to the development of acquired factor VIII inhibitors is an emerging clinical challenge in patients. Symptoms can occur suddenly with bleeding and/or bruising that is excessive relative to the degree of injury or severity of a comorbid condition. Diagnosis is difficult, and bleeding can quickly become life threatening if not treated promptly. This review provides current information, using a patient case scenario, to improve awareness and recognition of patients presenting unexpectedly with excessive bleeding of unknown etiology.

DATA SOURCES

To complete this review, a search of English-language publications was conducted using Medline and CINAHL databases (1966-2010).

CONCLUSIONS

Although development of acquired factor VIII inhibitors is rare, its incidence is increasing in many different patient care settings. Improved awareness and recognition is needed to mitigate the significant patient morbidity and mortality that can occur without rapid and timely treatment by experienced hematology specialists.

IMPLICATIONS FOR PRACTICE

Nurse practitioners, as front-line clinicians treating patients in various therapeutic areas, may be the first healthcare professionals who see patients with this disorder. Increased knowledge and awareness of this rare but potentially catastrophic cause of excessive bleeding can improve prompt treatment and optimize patient outcomes.

An Acquired Factor VIII Inhibitor in a Patient with HIV and HCV: A Case Presentation and Literature Review

Introduction. Despite its low incidence, acquired factor VIII inhibitor is the most common autoantibody affecting the clotting cascade. The exact mechanism of acquisition remains unclear, but postpartum patients, those with autoimmune conditions or malignancies, and those with exposure to particular drugs appear most susceptible. There have been several case reports describing acquired FVIII inhibitors in patients receiving interferon alpha for HCV treatment and in patients being treated for HIV. To our knowledge, this is the first case of a patient with HCV and HIV who was not actively receiving treatment for either condition. Case Presentation. A 57-year-old Caucasian male with a history of HIV and HCV was admitted to our hospital for a several day history of progressively worsening right thigh bruising and generalized weakness. CTA of the abdominal arteries revealed large bilateral retroperitoneal hematomas. Laboratory studies revealed the presence of a high titer FVIII inhibitor. Conclusion. Our case of a very rare condition highlights the importance of recognizing and understanding the diagnosis of acquired FVIII inhibitor. Laboratory research and clinical data on the role of newer agents are needed in order to better characterize disease pathogenesis, disease associations, genetic markers, and optimal disease management.

Acquired haemophilia A: a 2013 update

Acquired haemophilia A (AHA) is a rare but often severe bleeding disorder caused by autoantibodies against coagulation factor VIII (FVIII). AHA occurs more frequently in the elderly and in association with several conditions, such as the post-partum period, malignancies, autoimmune diseases or drug exposure; however, approximately 50% of reported cases are apparently idiopathic. Beside the elimination of the underlying disorder, the therapeutic approach to AHA should be directed toward the control of acute bleed and the eradication of FVIII autoantibody production. In this narrative review, we summarise the current knowledge on the epidemiology, diagnosis and clinical features of AHA, focusing in particular on advances in the management of this challenging bleeding disorder.

Gene therapy for hemophilia

Hemophilia A and B are X-linked monogenic disorders resulting from deficiencies of factor VIII and FIX, respectively. Purified clotting factor concentrates are currently intravenously administered to treat hemophilia, but this treatment is non-curative. Therefore, gene-based therapies for hemophilia have been developed to achieve sustained high levels of clotting factor expression to correct the clinical phenotype. Over the past two decades, different types of viral and non-viral gene delivery systems have been explored for hemophilia gene therapy research with a variety of target cells, particularly hepatocytes, hematopoietic stem cells, skeletal muscle cells, and endothelial cells. Lentiviral and adeno-associated virus (AAV)-based vectors are among the most promising vectors for hemophilia gene therapy. In preclinical hemophilia A and B animal models, the bleeding phenotype was corrected with these vectors. Some of these promising preclinical results prompted clinical translation to patients suffering from a severe hemophilic phenotype. These patients receiving gene therapy with AAV vectors showed long-term expression of therapeutic FIX levels, which is a major step forwards in this field. Nevertheless, the levels were insufficient to prevent trauma or injury-induced bleeding episodes. Another challenge that remains is the possible immune destruction of gene-modified cells by effector T cells, which are directed against the AAV vector antigens. It is therefore important to continuously improve the current gene therapy approaches to ultimately establish a real cure for hemophilia.

Management of patients with long-term inhibitors: is immune tolerance an underestimated life-long solution?

Immune tolerance induction (ITI) is recognized as the first choice treatment in haemophilic patients with inhibitors, with the aim of restoring safe and effective standard factor VIII replacement and, particularly, prophylaxis in children. For the latter, literature data and clinical practice support the optimal cost utility ratio of ITI. Indeed, the high success rate, the low incidence of inhibitor recurrence after successful ITI and the possibility of preventing joint deterioration, enable one to predict a considerable long-term reduction of costs in the majority of treated patients. Therefore, in spite of high costs and open issues about optimal regimens, ITI is actually attempted in virtually all children with inhibitors. Few patients with long-standing inhibitors presently undergo ITI, particularly in the case of severe bleeding tendency. In this setting, uncertainties concerning management are amplified by the paucity of literature data and psychological reluctance by both patients and treaters due to the perceived poor prognosis and the demanding treatment (also in terms of costs). However, clinical data suggest that the role of age at ITI start and of time interval from inhibitor diagnosis, as predictors of ITI outcome, should be considered in a larger framework of proposed and more established prognostic factors. Moreover, optimising ITI management, particularly with respect to inhibitor titre at ITI start and avoidance of adverse events or interruption of treatment, may also contribute to improve outcomes. Although the economic constraints of the present era significantly affect resources for such a high-cost treatment, the individual cost-utility ratio (bleeding tendency and risk of fatal bleeding, arthropathy and need for orthopaedic surgery, comorbidities, quality of life) should be assessed carefully to determine whether ITI is a suitable option and thus not preclude adults from the opportunity of inhibitor eradication.

Acquired factor XIII deficiency: a therapeutic challenge

Less than 60 cases of acquired factor (F)XIII deficiencies have been reported, most having distinct clinical features. To illustrate the therapeutic challenges of acquired FXIII inhibitors, we report a case of a 65-year-old patient with no previous bleeding history who suddenly developed massive haemorrhages associated to a strong and isolated FXIII inhibitor. No underlying disorder has been detected till now after three years of follow-up. Despite aggressive treatment with prednisone, rituximab, cyclophosphamide, immunoglobulin, immunoadsorption and immune tolerance his inhibitor is still present, although at low titre and with a clinical benefit since the patient has no more bleed since more than one year. Moreover the patient had a venous thromboembolic complication. After a review of the management of acquired FXIII deficiency patients and based on the management of acquired haemophilia we discuss a possible strategy for such difficult cases.

Nijmegen-Bethesda assay to measure factor VIII inhibitors

Hemophilia A is an inherited bleeding disorder caused by a deficiency of factor VIII coagulant activity (FVIII:C). Patients are treated with infusions of either plasma-derived or recombinant factor VIII. However, some patients develop inhibitory antibodies (inhibitors) to infused factor VIII which render it ineffective. The original Bethesda method was developed to standardize measurement of inhibitors in a factor VIII neutralization assay. One Bethesda unit is defined as that amount of inhibitor that results in 50% residual FVIII:C activity of a defined test mixture. In the Nijmegen modification of the original Bethesda method, the pH and the protein concentration of the test mixture is further standardized. As a result, the FVIII:C in the test mixture is less prone to artifactual deterioration and the test has improved specificity. Even with a standardized procedure a number of factors can affect the performance of the test and it is important for laboratory staff to be aware of their impact on the result outcome.

Therapeutic challenges in acquired factor VIII deficiency

Management of acquired hemophilia A is challenging and should be undertaken in close collaboration with a hemophilia center with expertise in the field. Treatment involves controlling and preventing bleeds and using immunosuppression to eradicate the inhibitor. Prompt diagnosis is important to allow early hemostatic treatment and to prevent nonessential invasive procedures. First-line hemostatic treatment should be with a bypassing agent. Recombinant activated factor VII and the activated prothrombin complex concentrate anti-inhibitor coagulant complex (Factor Eight Inhibitor Bypassing Activity, or FEIBA) but equally efficacious but both associated with thrombotic events when used in acquired hemophilia. Immunosuppression should be started as soon as a diagnosis has been confirmed. The combination of steroids and cyclophosphamide may induce more patients into remission than steroids alone. Current data do not suggest that rituximab results in better outcomes. Relapse is common (10%-20%) in the first 6 months after immunosuppression is stopped, and patients need to be followed up regularly to allow early diagnosis and treatment of relapse.

Potentiation of thrombin generation in hemophilia A plasma by coagulation factor VIII and characterization of antibody-specific inhibition

Development of inhibitory antibodies to coagulation factor VIII (fVIII) is the primary obstacle to the treatment of hemophilia A in the developed world. This adverse reaction occurs in 20-30% of persons with severe hemophilia A treated with fVIII-replacement products and is characterized by the development of a humoral and neutralizing immune response to fVIII. Patients with inhibitory anti-fVIII antibodies are treated with bypassing agents including recombinant factor VIIa (rfVIIa). However, some patients display poor hemostatic response to bypass therapy and improved treatment options are needed. Recently, we demonstrated that fVIII inhibitors display widely variable kinetics of inhibition that correlate with their respective target epitopes. Thus, it was hypothesized that for antibodies that display slow rates of inhibition, supplementation of rfVIIa with fVIII would result in improved thrombin generation and be predictive of clinical responses to this novel treatment regimen. In order to test this hypothesis, 10 murine monoclonal antibodies (MAbs) with non-overlapping epitopes spanning fVIII, differential inhibition titers, and inhibition kinetics were studied using a thrombin generation assay. Of the 3 MAbs with high inhibitory titers, only the one with fast and complete (classically defined as "type I") kinetics displayed significant inhibition of thrombin generation with no improvement upon supplementation of rfVIIa with fVIII. The other two MAbs that displayed incomplete (classically defined as "type II") inhibition did not suppress the potentiation of thrombin generation by fVIII. All antibodies that did not completely inhibit fVIII activity demonstrated potentiation of thrombin generation by the addition of fVIII as compared to rfVIIa alone. In conclusion, fVIII alone or in combination with rfVIIa corrects the thrombin generation defect produced by the majority of anti-fVIII MAbs better than single agent rfVIIa. Therefore, combined fVIII/rfVIIa therapy may provide better hemostatic control than current therapy in some patients with anti-fVIII inhibitors.

How I treat inhibitors in haemophilia

The management of patients with inhibitors is the greatest challenge facing haemophilia health professionals. Immune tolerance induction (ITI) can be successful in eliminating the inhibitor in the majority of patients, provided it is started soon after the inhibitor develops and the titre of the inhibitor is <10 BU at commencement of ITI. Acute bleeding is treated using one of two bypassing agents, which exhibit similar efficacy and safety. Surgery in inhibitor patients is challenging and should only be carried out in experienced centres.