Laboratory assessment of factor VIII inhibitor titer: the North American Specialized Coagulation Laboratory Association experience

International Council for Standardization in Haematology recommendations for laboratory measurement of factor VIII and FIX type I inhibitors

This guidance document has been prepared on behalf of the International Council for Standardisation in Hematology. The aim of the document is to provide guidance and recommendations on the measurement of factor VIII (FVIII) and factor IX (FIX) inhibitors. After an introduction on the clinical background and relevance of factor VIII and factor IX inhibitor testing, the following aspects of laboratory testing are included: screening for inhibitors, assay principle, sample requirements, testing requirements and interpretation, quality assurance, interferences and recent developments. This guidance document focusses on recommendations for a standardised procedure for the laboratory measurement of FVIII and FIX type I inhibitors. The recommendations are based on published data in peer-reviewed literature and expert opinion.

Hemophilia A: Emicizumab monitoring and impact on coagulation testing

Hemophilia A is an X-linked recessive bleeding disorder characterized by absent or ineffective coagulation factor VIII, a condition that could result in a severe and potentially life-threatening bleed. Although the current standard of care involves prophylactic replacement therapy of factor VIII, the development of neutralizing anti-factor VIII alloantibody inhibitors often complicates such therapeutic treatment. Emicizumab (Hemlibra®), a novel recombinant therapeutic agent for patients with hemophilia A, is a humanized asymmetric bispecific IgG4 monoclonal antibody designed to mimic activated factor VIII by bridging factor IXa and factor X thus effecting hemostasis. Importantly, this drug eliminates the need for factor VIII and complications associated with inhibitor generation. Emicizumab has been approved for use in several countries including the United States and Japan for prophylaxis of bleeding episodes in hemophilia A with and without FVIII inhibitors. Therapy is also approved in the European Union for routine prophylaxis of bleeds in hemophilia A with inhibitors or severe hemophilia A without inhibitors. Unfortunately, emicizumab therapy presents unique challenges for routine and specialty coagulation tests currently used to monitor hemophilia A. In this review, hemophilia A is presented, the biochemistry of factor VIII is discussed, and the impact of the therapeutic agent emicizumab is highlighted.

Ungewöhnlicher Suizid durch Verbluten aus einer Hautvene

Ein 90-jähriger Mann verstarb durch protrahiertes Verbluten aus einer, mittels Rasierklinge minimal eröffneten, oberflächlichen Beinvene über der Patella und nachfolgender Manipulation. Dabei handelte es sich wahrscheinlich um einen Ast der V. saphena accessoria anterior. Es lag zunächst eine Fehleinschätzung durch den leichenschauhaltenden Arzt vor, der von einer gastrointestinalen Blutung als Todesursache ausging. Diese Einschätzung teilten die Kriminalbeamten aufgrund der Auffindesituation nicht. Begünstigend war eine vorbestehende Varikosis. Die Einnahme von Antikoagulanzien oder eine vorbestehende oder erworbene Gerinnungsstörung konnte nicht nachgewiesen bzw. eruiert werden. Bei Vorlage eines Abschiedsbriefes und Ausschluss fremder Gewalteinwirkungen oder einer Vergiftung kann plausibel von einem ungewöhnlichen suizidalen Ereignis ausgegangen werden. Es wird über die Auffindung sowie die Ergebnisse der Sektion und umfangreicher Zusatzuntersuchungen berichtet.

Advantages of external quality assessment-EQA programs

INTRODUCTION

The first external quality assessment (EQA) in Thrombosis and Haemostasis was elaborated over 20 years ago, and since then, several national and international EQA institutions have been established.

AIM

Display the benefits of EQA programs.

METHODS

The spectrum of EQA action was evaluated ranges from improving the performance of the local laboratory to highlighting inadequate diagnostic tests that need to be replaced by new technologies.

RESULTS

The first result approach is related to a national management of quality in laboratories. In recent years, Brazil has invested in an EQA program to aid public policy in the laboratory area. During this period, a group of haemostasis laboratory specialists were invited to manage the results and help the Ministry of Health with applying these results as a strategy to improve laboratories. Thus, in collaboration with NEQAS-BC, the University of Campinas - UNICAMP, established a Brazilian EQA program for Blood Coagulation. The second result approach is related to FVIII inhibitor assay performance evaluation, which is another type of EQA program benefit. Despite the assay being considered the gold standard to measure neutralised immunoglobulins for FVIII since 1975, over 40 years ago, the test still has a high coefficient of variation. Results from NEQAS-BC and WFH IEQAS program demonstrate the inter-laboratory variation across the United Kingdom over the last years and among emergent countries.

CONCLUSION

The EQA programs have an important educational role in helping countries manage their public policy and in the international inquiry regarding the necessity of new technologies in haemostasis.

Acquired Factor VIII Inhibitors: A Case Study

The physiology of hemostasis is one of high complexity that involves the initiation, amplification, and propagation of the many moving parts of the hemostatic system and its regulatory mechanisms. It is imperative that clinical laboratory professionals have a strong understanding of the many intricacies of the physiology of coagulation and its in vitro testing. An elongated activated partial thromboplastin time can have several causes, and the correct cause must be elucidated in a timely manner for proper treatment. A mixing study with normal pooled plasma should be performed to evaluate for the presence of an inhibitor vs factor deficiency. Factor inhibitors, specifically factor VIII in this case study, should be titered so that the clinician can decide which treatment may work best for the patient. Continued monitoring of factor levels and inhibitor titers should be conducted to follow the resolution or progression of inhibitor presence.

Predictive significance of anti-FVIII immunoglobulin patterns on bleeding phenotype and outcomes in acquired hemophilia A: Results from the Quebec Reference Center for Inhibitors

BACKGROUND

Acquired hemophilia A (AHA) is a potentially life-threatening bleeding disorder caused by factor VIII (FVIII) autoantibodies, involving various immunoglobulin (Ig) isotypes and IgG subclasses.

OBJECTIVES

We analyzed the profile of Ig against FVIII in patients with AHA to identify Ig patterns predictive of bleeding phenotype and outcomes.

PATIENTS/METHODS

Ig detection and titration were determined by enzyme-linked immunosorbent assay (ELISA) at disease presentation in a cohort of 66 subjects from the Quebec Reference Centre for Inhibitors registry.

RESULTS

Most of plasma samples analyzed (97%) contained multiple anti-FVIII Ig isotypes and IgG subclasses, IgG(1,2,3,4) (24.2%), [IgG(1,2,3,4),IgA] (16.7%) and IgG(2.4) (13.6%) being the most prevalent combinations of Ig detected. AHA patients who presented with IgA antibodies were more likely to have an associated auto-immune disease (p = .049). The presence of IgG4-was associated with bleeding symptoms at presentation (p = .002). IgG1-positive patients were more likely to require transfusions with red packed cell (p = .014) whereas IgM detection was associated with a higher probability of death linked to AHA (p = .011).

CONCLUSION

The Ig pattern of AHA patients at diagnosis is widely heterogeneous and is at least partially associated with some underlying conditions. Our data supports the differential predictive significance for IgG1, IgG4 and IgM on bleeding severity and suggests that the early determination of Ig profile may help to identify AHA patients at higher risk of poorer outcomes.

Unexplained hemorrhagic syndrome? Consider acquired hemophilia A or B

There is a dire need to develop an algorithm to improve the recognition of acquired hemophilia A and B (AHA and AHB) in clinical practice. Initial and intensive care unit (ICU) management of the disorder is particular and represents a challenge for the internist/hematologist and the ICU physician. A delay in the proper treatment of bleeding episodes can lead to a life-threatening event. Expert advice should be sought as soon as possible. Succesful resolution involves accurate diagnosis, bleeding control with hemostatic and immunotherapy, and eradication of the autoantibodies to improve overall survival. Current treatment guidelines are based on the literature in the form of cases and observational studies due to a lack of randomized controlled trials. AH can be triggered by many pathologies, presenting as a paraneoplastic syndrome in case of malignancies or as surgical associated acquired hemophilia (SAHA). We have reviewed the literature from 2015 to 2021 regarding the new case reports to further assess if there is an improvement in the clinical approach.

A Rare Case of Factor VII Inhibitor in a Patient Presenting with Primary Splenic Marginal Zone Lymphoma

BACKGROUND Here, we report the novel presentation of a factor VII inhibitor in association with a new diagnosis of splenic marginal zone lymphoma in a previously healthy 38-year-old woman. There are only 4 reported cases of factor VII inhibitors, none of which are secondary to a splenic marginal zone lymphoma. CASE REPORT Our patient, a 38-year-old woman, presented reporting increased abdominal swelling and early satiety. She was found to have pancytopenia, an elevated international normalized ratio (INR), normal partial thromboplastin time (PTT), and massive splenomegaly. Further investigation revealed a morphology and immunophenotype most consistent with splenic marginal zone lymphoma. A mixing study was unable to bring the INR into normal range after 60 min, confirming a factor VII inhibition. Therefore, the final diagnosis was primary splenic marginal zone lymphoma and secondary factor VII inhibitors. Owing to the elevated INR, both chemotherapy and splenectomy were avoided and we began a 4-week course of weekly rituximab infusions. After a second course of 4 treatments, there was a resolution of both the coagulopathy and the splenomegaly. At this point, the splenectomy was safely performed. Maintenance rituximab continued for 2 years. Our patient has now been in remission 12 years. CONCLUSIONS We successfully treated a rare factor VII inhibitor and its underlying splenic marginal zone lymphoma with rituximab immunotherapy. A complete response was documented by splenectomy. The patient's 12-year remission of both the lymphoma and the inhibitor helps to support the causative relationship between the lymphoma and the factor VII inhibitor.

Factor VIII/IX inhibitor testing practices in the United Kingdom: Results of a UKHCDO and UKNEQAS national survey

INTRODUCTION

Inhibitor formation is the greatest challenge facing persons with haemophilia treated with factor concentrates. The gold standard testing methodologies are the Nijmegen-Bethesda assay (NBA) for FVIII and Bethesda assay (BA) for FIX inhibitors, which are affected by pre-analytical and inter-laboratory variability.

AIMS

To evaluate inhibitor testing methodology and assess correlation between self-reported and actual methodology.

METHODS

Methodology was evaluated using a survey distributed alongside a UK National External Quality Assessment Service Blood Coagulation external quality assurance (EQA) exercise for FVIII and FIX inhibitor testing.

RESULTS

Seventy four survey and EQA exercise responses were received (response rate 63.2%), with 50 paired survey/EQA results. 47.1% (33/70) reported using the NBA and 42.9% (30/70) the BA for FVIII inhibitor testing. Review of FVIII inhibitor assay methodology demonstrated discrepancy (self-reported to actual) in 64.3% (BA reporting) and 27.6% (NBA reporting). Pre-analytical heat treatment was used by 32.4%, most commonly 56°C for 30 minutes. Assay cut-offs of 0.1-1.0 BU/mL were reported. EQA samples (acquired FVIII and congenital FIX) demonstrated titres and coefficients of variation (CV) of 3.1 BU/mL (0.7-15.4 BU/mL; CV = 43%) and 18.0 BU/mL (0-117 BU/mL; CV = 33%), respectively. No significant assay or laboratory factors were found to explain this variance, which could have resulted in change in management for 6 patients (5 misclassified high-titre FVIII inhibitors and 1 false negative for a FIX inhibitor).

CONCLUSIONS

Heterogeneity was seen at each stage of assay methodology. No assay-related factors were found to explain variation in inhibitor titres. Further standardization is required to improve inhibitor quantification to guide patient care.

Discordance between platelet-supported and vesicle-supported factor VIII activity in the presence of anti-C2 domain inhibitory antibodies

BACKGROUND

We recently reported that factor VIII (FVIII) binds to a macromolecular complex including fibrin on thrombin-stimulated platelets and that two antibodies against FVIII diminish platelet-supported FVIII activity more than vesicle-supported activity. The C2 domain of FVIII is known to bind to phospholipid membrane and also binds fibrin.

OBJECTIVES

We asked whether the degree of inhibition by anti-C2 antibodies would show differences between platelet-supported and the standard activated partial thromboplastin time (aPTT) assay.

METHODS

We evaluated the inhibition by a well-defined panel of monoclonal anti-C2 domain antibodies encompassing the major epitopes of the C2 domain. Activity was measured in an activated platelet time (aPT) assay containing fresh, density gradient-purified human platelets.

RESULTS

The aPT exhibited a log-linear relationship between FVIII and time to fibrin formation over a 4-log range, encompassing 0.01% to 100% plasma FVIII. Nine of 10 mAbs inhibited 89% to 96% of FVIII activity, whereas mAb F85 did not. There was no correlation between the degree of inhibition in the aPTT-based assay and the platelet assay. In particular, four mAbs did not inhibit the aPTT assay, yet inhibited 90% of platelet-based activity. Residual FVIII activity in purified-protein assays, relying on platelets, correlated with the aPT assay.

CONCLUSIONS

The degree of FVIII impairment by some inhibitor antibodies is substantially different on platelet membranes vs synthetic vesicles. Thus, current inhibitor assays may underestimate the frequency of significant inhibitors, and a platelet-based assay may more accurately assess bleeding risk.

An In Silico Exploration of the Factors That Affect the Precision of the Bethesda Assay

OBJECTIVES

Despite more than 40 years of experience performing the Bethesda assay (BA), poor intra- and interlaboratory precision remains the biggest laboratory challenge to date.

METHODS

The BA procedure was modeled using stochastic simulation techniques to determine the precision of the BA up to dilutions of 1:4,096, to estimate the minimum significant relative change at various inhibitor titers, and to understand the laboratory procedural variables that could significantly affect the performance of the BA at high dilutions.

RESULTS

Selecting the lowest dilution tube with a residual activity closest to 25% for calculating the reported Bethesda titer (BT), using a factor activity assay with a coefficient of variation less than or equal to 7.5% in the range of 15% to 50% factor activity level, performing the factor activity measurement in replicates, and minimizing pipette volumetric error resulted in the lowest imprecision in the reported BT. The factor neutralization kinetics of the inhibitor appear to have little impact on the precision of the assay if the incubation time is greater than 90 minutes.

CONCLUSIONS

This in silico model will assist future laboratory efforts in standardizing the quantification of specific coagulation factor inhibitors and improving the precision of the reported results.

Clinical utility of sample preheat treatment in a modified Nijmegen-Bethesda assay (mNBA) for inhibitor monitoring in congenital and acquired haemophilia A: A single-centre four-year experience

INTRODUCTION

Laboratory monitoring for factor VIII inhibitors ideally requires samples with the lowest possible factor VIII (FVIII) level, potentially challenging in patients with congenital haemophilia A (CHA) receiving regular prophylaxis and acquired haemophilia A (AHA) patients with endogenous FVIII. Inactivation of FVIII by preheating (preheat treatment, PHT) of patient plasma has been suggested to facilitate monitoring.

AIM

To evaluate the clinical utility of PHT prior to inhibitor analysis by modified Nijmegen-Bethesda assay (mNBA) in patients with CHA and AHA.

METHODS

Inhibitor screening by mNBA under standard conditions and with PHT at 56°C for 30, 60 and 90 minutes was evaluated. FVIII inhibitor results between 2007 and 2010 without PHT (720 results from 222 CHA and AHA patients), and between 2011 and 2014 post-PHT (1102 results from 302 patients) were available for analysis.

RESULTS

Of total 1822 results available, 61% were from severe HA patients, 22% from mild and moderate HA and 16% from AHA. Pre-PHT, 74% of samples were analysed by the mNBA, and the remaining 26% were not tested as FVIII levels were >20 IU/dL as per local protocol. Postintroduction of PHT (90 and 60 minutes), 96% of samples received were analysed for an inhibitor. Post-PHT in patients with AHA (n = 26), 69% of samples tested with factor VIII levels >20 IU/dL were found to have detectable inhibitor.

CONCLUSION

FVIII inhibitor testing using PHT at 56°C for 60 minutes facilitates inhibitor surveillance of CHA on prophylaxis. Potentially, 30 minutes at 56°C might be equally efficacious. In AHA receiving immunosuppression, monitoring of inhibitor titre after initial factor VIII response might enable personalized immunosuppression.

Mixing-based inhibitor screening in haemophilia A: challenges in interpretation

: Inhibitor development in haemophilia A patients is a dreaded complication of factor VIII (FVIII) replacement therapy. With increasing use of FVIII replacement therapy, there is an imperative need for cost-effective and standardized screening. To evaluate the efficacy of mixing-based inhibitor screening (MBIS) in the detection of FVIII inhibitors and to assess the best cut-off values for MBIS. Forty inhibitor positive and 40 inhibitor negative haemophilia A patients, diagnosed by standard criteria, with detailed clinical, haematological and on-demand treatment records were included. MBIS was evaluated in all 80 cases and a classical Bethesda assay and Nijmegen modification of Bethesda assay (NBA) were used as gold standards for inhibitor diagnosis. Classical Bethesda assay missed eight cases, most with low titres, which were confirmed by NBA. A systematic analysis of cut-offs for MBIS using a receiver operating characteristic curve fixed the cut-off at more than 5 s. MBIS detected 36 out of 40 inhibitor positive haemophilia A patients with a sensitivity, specificity, PPV and NPV of 90.0, 95, 94.7, 90.5%, respectively, whereas at the conventional cut-off of more than 10 s, MBIS detected only 25 of 40 cases with a low sensitivity of 62.5%. The likelihood ratio of a positive test was 11. The false-negative haemophilia A patients had low titres from 1.6 to 4.2 BU/ml. MBIS at a cut-off of 5 s can be considered as an effective screening test in low-resource situations. In clinical situations and in cases with clinical evidence of inhibitors we recommend that a direct NBA should be done.

Acquired Hemophilia A: A Case Report

Hemophilia A, also known as factor VIII deficiency, is a rare disorder caused by an insufficient level of factor VIII, an essential clotting protein. Hemophilia A can be inherited or acquired. Inherited hemophilia A is caused by a mutation to the factor VIII gene on the X chromosome, which is commonly passed down from parents to children. However, in about one-third of cases, the cause is a spontaneous mutation in that gene. Acquired hemophilia A is due to an autoantibody to factor VIII, which is termed an inhibitor. This rare disorder can cause life-threatening bleeding complications. Management relies on a rapid and accurate diagnosis, control of bleeding episodes, and eradication of the inhibitor by immunosuppression therapy. Most treatment strategies are centered around anecdotal reports or small case series. This case report summarizes the successful treatment of a patient with acquired hemophilia A and major bleeding following a surgical procedure, with the use of desmopressin, recombinant factor VIIa, repeated doses of recombinant factor VIII, rituximab, and prednisone.

Distinguishing lupus anticoagulants from factor VIII inhibitors in haemophilic and non-haemophilic patients

INTRODUCTION

Accurate diagnosis of an inhibitor, a neutralizing antibody to infused factor VIII (FVIII), is essential for appropriate management of haemophilia A (HA). Low-titre inhibitors may be difficult to diagnose due to high rates of false-positive inhibitor results in that range. Transient low-titre inhibitors and false-positive inhibitors may be due to the presence of a lupus anticoagulant (LA) or other non-specific antibodies. Fluorescence immunoassay (FLI) to detect antibodies to FVIII is a sensitive method to identify inhibitors in HA. Evaluations of antibody profiles by various groups have demonstrated that haemophilic inhibitors detected by Nijmegen-Bethesda (NBA) and chromogenic Bethesda (CBA) assays correlate with positivity for anti-FVIII immunoglobulin (Ig) G1 and G4.

AIM

This study sought to determine whether FLI could distinguish false-positive FVIII inhibitor results related to LAs from clinically relevant FVIII inhibitors in HA patients.

METHODS

Samples from haemophilic and non-haemophilic subjects were tested for LA, specific FVIII inhibitors by NBA and CBA, and anti-FVIII immunoglobulin profiles by FLI.

RESULTS

No samples from LA-positive non-haemophilic subjects were positive by FLI for anti-FVIII IgG4. Conversely, 91% of NBA-positive samples from haemophilia subjects were positive for anti-FVIII IgG4. Two of 11 haemophilia subjects had samples negative for anti-FVIII IgG4 and CBA, which likely represented LA rather than FVIII inhibitor presence.

CONCLUSIONS

Assessment of anti-FVIII profiles along with the CBA may be useful to distinguish a clinically relevant low-titre FVIII inhibitor from a transient LA in HA patients.

Acquired Hemophilia of Unknown Etiology in an Elderly Man: Case Report

BACKGROUND Acquired hemophilia is a rare but potentially dangerous bleeding disorder caused by autoantibodies against coagulation factors. It affects 1 to 1.5 per 1 million people each year. While 50% of cases could be idiopathic, other causes include malignancies, diabetes, pregnancy, infection, and autoimmune disorders. CASE REPORT We report a case of a 90-year-old male who developed a spontaneous hematoma on the dorsum of his right hand, with no prior history of trauma or any other mucosal bleeding. His activated partial thromboplastin time (aPTT) was found to be prolonged (>180 seconds) with a very low level of factor VIII (0.1%). CONCLUSIONS As workups did not identify the source, including malignancy and autoimmune diseases, of his acquired hemophilia, it is believed to be idiopathic. He was started on intravenous recombinant factor VIIa (NovoSeven) to control the bleeding in combination with an immunosuppressive therapy of cyclophosphamide and prednisolone. In approximately 10% of patients with acquired hemophilia, underlying malignancy, such as squamous cell cancer, chronic lymphocytic leukemia, non-Hodgkin lymphoma, and multiple myeloma can present and commonly develop in elderly patients. Therefore, patients diagnosed with idiopathic acquired hemophilia should be given long-term follow up.

Novel assays in the coagulation laboratory: a clinical and laboratory perspective

The ability to monitor Factor VIII (FVIII) and Factor IX (FIX) levels is integral to the clinical management of hemophilia A and B patients, respectively. Factor activity levels are checked during regular follow-up, post-infusion of factor concentrates, during pre- and post-operative assessments, and when the presence of an inhibitor is suspected. However, the ability to accurately and reproducibly measure factor activity levels with standard coagulation assays has been challenging due to the emergence of recombinant factor concentrates with extended half-lives. Similarly, special considerations must be given to the type of inhibitor assay used in patients with acquired hemophilia receiving recombinant porcine FVIII replacement. Alternative approaches to achieve hemostasis with clotting factor mimetics and interference of endogenous anticoagulants lack standardized assays for monitoring hemostatic efficacy. Laboratory assays measuring dynamic clotting parameters such as thrombin generation or whole blood viscoelasticity may provide a way forward, but have yet to enter routine clinical use. This review highlights the role of specialized coagulation assays in an era where multiple new hemostatic therapeutics for hemophilia are available, and underscores the need for clear communication between bedside and laboratory clinicians.

Usefulness of chromogenic assays for potency assignment and recovery of plasma-derived FVIII and FIX concentrates or their recombinant long acting therapeutic equivalents with potential application in treated pediatric hemophiliac patients

On demand and prophylaxis usage of FVIII/ FIX concentrates for the therapeutic management of hemophilia has greatly changed quality of life, and healthy life span of affected patients. Availability of recombinant therapeutic FVIII and FIX products, and of their long-acting variants, further improves the treatment constraints, and progressively permits to hemophiliacs to have an almost normal way of life. Unlimited amounts of recombinant or engineered substitutive products become available, and open new avenues for extending the benefits of prophylaxis to all hemophiliac patients, not only in economically advanced territories, but also in emerging and developing countries, worldwide. Pharmacokinetics of injected products can be variable among treated patients, and dependent on age. In addition, patient medical status, existing diseases, and the nature of joint damages can impact protective effect of substitutive products, and risks associated to way of life and activity. Product requirements and half-life of infused products are therefore patient specific. Monitoring recoveries of injected products thus provide useful information for the most appropriate treatment adjustment. FVIII and FIX measurements in plasma of treated patients helps to establish the optimal interval between injections for each treated patient, and the overall therapeutic cost. Due to the high variability from reagent to reagent, and the different behavior from plasma derived products, clotting methods are not ideal for recombinant and long-acting products. They require to be performed only in association with a drug specific calibrator. They are not recommended for patients' survey, due to the high variety of reagents available. Chromogenic assays (2-stage methods) offer a standard reactivity to all available FVIII or FIX products in drugs, whether the way they are obtained, or in plasma. In a subset of treated patients, inhibitory antibodies to FVIII or FIX develop and can be measured with inhibition assays (Bethesda units), or by Elisa. Unfortunately, FVIII or FIX substitutive therapies cannot be used in patients with inhibitors, and alternative clinical management is requested, such as the use of FEIBA or FVIIa for their bypassing activity. A new treatment is being introduced in the form of a bispecific antibody (Emicizumab) targeted to both FIXa and FX, and which allows activating FX by FIXa without the need for FVIII. Some chromogenic assays (Biophen FVIII), designed with human proteins, offer the possibility to measure the activity and recovery of this new drug. Chromogenic methods are then useful for establishing potency of therapeutic products or monitoring recovery and kinetics in treated patients, through plasma measurements. Availability of International Standards for FVIII and FIX, in concentrates or plasma, allows harmonization of assay results.

Towards harmonization of external quality assessment/proficiency testing in hemostasis

Quality in diagnostic testing represents a key target of laboratory medicine, for which an assurance around the quality of testing is expected from all involved in the process. Laboratories attempt to assure the quality of their testing by various processes, but especially by performance of internal quality control and external quality assessment (EQA). This is especially true for tests of hemostasis and coagulation. EQA in general provides information on test accuracy and on evaluation of long-term laboratory performance. EQA providers support laboratory performance by various means, including distribution of material for testing of analytes (“proficiency testing”), educational support through expert advice, distribution of publications or case series. Participation in EQA is often a laboratory accreditation requirement. This review aims to identify some of the strengths and weaknesses of EQA, and targets attempts towards harmonization of EQA practice, in order to achieve the best outcome for participant laboratories and, thus, for patients and their clinical care providers.

Laboratory testing for factor VIII and IX inhibitors in haemophilia: A review

Inhibitors are antibodies directed against haemophilia treatment products which interfere with their function. Factor VIII (FVIII) inhibitors in haemophilia A and factor IX (FIX) inhibitors in haemophilia B are significant clinically when they require a change in a patient's treatment regimen. Their persistence may increase morbidity and mortality. Multiple laboratory tests are now available for detecting and understanding inhibitors in haemophilia. Inhibitors are traditionally measured by their interference in clotting or chromogenic factor assays. They may also be detected using immunologic assays, such as enzyme-linked immunosorbent assay or fluorescence immunoassay. Anti-FVIII or anti-FIX antibodies of IgG4 subclass best correlate with the presence of functional inhibitors. Improvements in inhibitor measurement have been recently introduced. Preanalytical heat treatment of patient specimens allows testing of patients without delaying treatment. Use of chromogenic and immunologic assays may aid in identification of false-positive results, which are frequent among low-titre inhibitors. Validated reagent substitutions can be used to reduce assay cost. New methods for defining assay positivity and reporting low-titre inhibitors have been suggested. Challenges remain in the areas of quality control, assay standardization, monitoring of patients undergoing immune tolerance induction therapy and testing in the presence of modified and novel treatment products.

Diagnostic accuracy study of a factor VIII ELISA for detection of factor VIII antibodies in congenital and acquired haemophilia A

Antibody formation to factor VIII (FVIII) remains the greatest clinical and diagnostic challenge to the haemophilia-treating physician. Current guidance for testing for inhibitory FVIII antibodies (inhibitors) recommends the functional Nijmegen-Bethesda assay (NBA). A FVIII ELISA offers a complementary, immunological approach for FVIII antibody testing. It was the aim of this study to retrospectively evaluate the performance of a FVIII ELISA (index) for detection of FVIII antibodies, compared with the NBA (reference). All samples sent for routine FVIII antibody testing at two haemophilia Comprehensive Care Centres, were tested in parallel using the NBA and a solid-phase, indirect FVIII ELISA kit (Immucor). A total of 497 samples from 239 patients (severe haemophilia A=140, non-severe haemophilia A=85, acquired haemophilia A=14) were available for analysis. Sixty-THree samples tested positive by the NBA (prevalence 12.7 %, 95 % confidence interval [CI], 9.9–15.9 %), with a median inhibitor titre of 1.2 BU/ml (range 0.7–978.0). The FVIII ELISA demonstrated a specificity of 94.0 % (95 %CI, 91.3–96.0), sensitivity of 77.8 % (95 %CI, 65.5–87.3), negative predictive value of 96.7 % (95 %CI, 94.5–98.2), positive predictive value 65.3 % (95 %CI, 53.5–76.0), negative likelihood ratio 0.2 (95 %CI, 0.1–0.4), positive likelihood ratio 13.0 (95 %CI, 8.7–19.3) and a diagnostic odds ratio of 54.9 (95 %CI, 27.0–112.0). Strong positive correlation (r=0.77, p< 0.001) was seen between the results of the NBA (log adjusted) and FVIII ELISA optical density. In conclusion, FVIII ELISA offers a simple, specific, surveillance method enabling batch testing of non-urgent samples for the presence of FVIII antibodies.

Limit of detection and threshold for positivity of the Centers for Disease Control and Prevention assay for factor VIII inhibitors

Essentials Immunologic methods detect factor VIII (FVIII) antibodies in some inhibitor-negative specimens. Specimens were tested by modified Nijmegen-Bethesda assay (NBA) and fluorescence immunoassay. The NBA with preanalytical heat inactivation detects FVIII inhibitors down to 0.2 NBU. IgG4 frequency validates the established threshold for positivity of ≥ 0.5 NBU for this NBA.

SUMMARY

Background The Bethesda assay for measurement of factor VIII inhibitors called for quantification of positive inhibitors by using dilutions producing 25-75% residual activity (RA), corresponding to 0.4-2.0 Bethesda units, with the use of 'more sensitive methods' for samples with RA closer to 100% being recommended. The Nijmegen modification (Nijmegen-Bethesda assay [NBA]) changed the reagents used but not these calculations. Some specimens negative by the NBA have been shown to have FVIII antibodies detectable with sensitive immunologic methods. Objective To examine the performance at very low inhibitor titers of the Centers for Disease Control and Prevention (CDC)-modified NBA (CDC-NBA), which includes preanalytic heat inactivation to liberate bound anti-FVIII antibodies. Methods Specimens with known inhibitors were tested with the CDC-NBA. IgG4 anti-FVIII antibodies were measured by fluorescence immunoassay (FLI). Results Diluted inhibitors showed linearity below 0.4 Nijmegen-Bethesda units (NBU). With four statistical methods, the limit of detection of the CDC-NBA was determined to be 0.2 NBU. IgG4 anti-FVIII antibodies, which correlate most strongly with functional inhibitors, were present at rates above the background rate of healthy controls in specimens with titers ≥ 0.2 NBU and showed an increase in frequency from 14.3% at 0.4 NBU to 67% at the established threshold for positivity of 0.5 NBU. Conclusions The CDC-NBA can detect inhibitors down to 0.2 NBU. The FLI, which is more sensitive, demonstrates anti-FVIII IgG4 in some patients with negative (< 0.5) NBU. The sharp increase in IgG4 frequency between 0.4 and 0.5 NBU validates the established threshold for positivity of ≥ 0.5 NBU for the CDC-NBA, supporting the need for method-specific thresholds.

The Development of FVIII Inhibitors in Relation to IL10 Gene Polymorphism in Hemophilia A Egyptian Pediatric Patients

BACKGROUND

Development of inhibitors against Factor VIII (FVIII) in hemophilia A patients is a serious complication of therapy. Many cytokines, including interleukin-10 (IL10), may affect inhibitor development; however, literature data are not sufficient to prove this association. The aim of this study was to investigate the relation between FVIII inhibitor formation and IL10-1082A/G polymorphism among Egyptian hemophiliacs.

METHODS

Patients were screened for FVIII inhibitors using the Bethesda method. IL10-1082A/G polymorphism was detected by polymerase chain reaction-restriction fragment length polymorphism.

RESULTS

Six patients (12%) developed inhibitors. No statistically significant difference was found between inhibitor positive and negative patients regarding IL10-1082A/G genotypes, disease severity, or treatment-related variables (type of FVIII received, treatment regimen, age at first exposure to FVIII, and frequency of replacement therapy).

CONCLUSIONS

FVIII inhibitor formation in this group of Egyptian hemophiliacs was not correlated to IL10-1082A/G polymorphism, disease severity, or any of the treatment variables.

Clinical characteristics and outcomes of acquired hemophilia A: experience at a single center in Japan

Acquired hemophilia A (AHA), which is caused by autoantibodies against coagulation factor VIII (FVIII) is a rare, life-threatening bleeding disorder, the incidence of which appears to be increasing in Japan as the population ages. However, the clinical characteristics, treatment, and outcomes of AHA remain difficult to establish due to the rarity of this disease. We retrospectively analyzed data from 25 patients (median age 73 years; range 24-92 years; male n = 15) diagnosed with AHA between 1999 and 2015 at Gunma University Hospital. We identified autoimmune diseases and malignancy as underlying conditions in four and three patients, respectively. Factor VIII activity was significantly decreased in all patients (median 2.0%; range <1.0-8.0) by FVIII inhibitor (median 47.0 BU/mL; range 2.0-1010). Among 71 bleeding events, subcutaneous or intramuscular hemorrhage was the most prevalent. Seventeen patients required bypassing agents. Twenty-two (91.7%) of 24 patients treated with immunosuppressive agents achieved complete response (CR) during a median of 57.5 days (range 19-714 days). Although three patients (12%) relapsed and seven (28%) died of infection, none of the deaths were related to bleeding. Although most of our patients achieved CR after immunosuppressive therapy, the rate of infection-related mortality was unsatisfactorily high.

The impact of the immune system on the safety and efficiency of enzyme replacement therapy in lysosomal storage disorders

In the light of clinical experience in infantile onset Pompe patients, the immunological impact on the tolerability and long-term efficacy of enzyme replacement therapy (ERT) for lysosomal storage disorders has come under renewed scrutiny. This article details the currently proposed immunological mechanisms involved in the development of anti-drug antibodies and the current therapies used in their treatment. Given the current understanding of the adaptive immune response, it focuses particularly on T cell dependent mechanisms and the paradigm of using lymphocytic negative selection as a predictor of antibody formation. This concept originally postulated in the 1970s, stipulated that the genotypically determined lack of production or production of a variant protein determines an individual's lymphocytic repertoire. This in turn is the key factor in determining the potential severity of an individual's immunological response to ERT. It also highlights the need for immunological assay standardization particularly those looking at describing the degree of functional impact, robust biochemical or clinical endpoints and detailed patient subgroup identification if the true evaluations of impact are to be realised.

Alloantibodies to therapeutic factor VIII in hemophilia A: the role of von Willebrand factor in regulating factor VIII immunogenicity

The rising incidence of neutralizing antibodies (inhibitors) against therapeutic factor VIII prompted the conduct of studies to answer the question as to whether this rise is related to the introduction of recombinant factor VIII products. The present article summarizes current opinions and results of non-clinical and clinical studies on the immunogenic potential of recombinant compared to plasma-derived factor VIII concentrates. Numerous studies provided circumstantial evidence that von Willebrand factor, the natural chaperone protein present in plasma-derived factor VIII products, plays an important role in protecting exogenous factor VIII from uptake by antigen presenting cells and from recognition by immune effectors. However, the definite contribution of von Willebrand factor in reducing the inhibitor risk and in the achievement of immune tolerance is still under debate.

Characteristics of hemophilia patients with factor VIII inhibitors detected by prospective screening

Characteristics of inhibitors identified by prospective screening may differ from those detected clinically. In a prospective study at 17 hemophilia centers with central inhibitor measurement by Nijmegen-Bethesda assay, 23 (2.8%) of 824 hemophilia A patients had new inhibitors detected: nine high-titer inhibitors (HTI: 7 ≥ 5.0 NBU plus 2 of 2.6 and 3.4 NBU at immune tolerance induction initiation) and 14 low-titer inhibitors (LTI: 0.5-1.9 NBU). HTI occurred at an earlier age (median 2 years, range 1-18, vs. median 11 years, range 2-61, P = 0.016). Both HTI (22%) and LTI (43%) occurred in non-severe patients. All HTI, but only 64% of LTI, were found to be FVIII-specific by chromogenic Bethesda assay or fluorescence immunoassay (FLI), indicating a high rate of false-positive LTI. Repeat specimens confirmed all HTI, 7/9 LTI, and 7/7 FVIII-specific LTI. FLI results were similar between HTI and FVIII-specific LTI; all included IgG1 and IgG4 subclasses. A comparable prospective study conducted from 1975 to 1979 at 13 U.S. centers found 31 (2.4%) new inhibitors among 1,306 patients. In both studies, one-third of inhibitors occurred in non-severe patients and one-quarter after 150 exposure days (ED). Significant differences were seen in the age at which inhibitors occurred (median 16 years in the older study vs. 5 years currently, P = 0.024) and in ED before inhibitor development, 10% in the older study and 43% currently study occurring within 20 ED, suggesting a temporal change in inhibitor development. Prospective screening detects inhibitors in patients of all severities, ages, and ED. Some LTI, however, are false positives.

The role of previously untreated patient studies in understanding the development of FVIII inhibitors

Development of inhibitors against factor VIII (FVIII), the major complication of haemophilia A treatment today, is influenced by multiple factors. Genetic (F8 mutation, family history, ethnicity, polymorphisms in immune modulating genes) and non-genetic (intensive exposure to FVIII, presence of pro-inflammatory signals as might occur with large bleeds, infections, surgery, or other immune stimulants [e.g. vaccines]) risk factors as well as their complex inter-relationships contribute to the inhibitor risk profile of haemophilia patients, particularly in the previously untreated patient (PUP) population. Studies in PUPs have been fundamental to furthering the understanding of FVIII inhibitor development, as well as discovering previously unappreciated risk factors. The multi-factorial nature of inhibitor development makes it difficult to ascertain the contribution of FVIII products in inhibitor development through individual PUP studies. Sufficiently powered studies of large cohorts may overcome these limitations but interpretations should be conducted cautiously. Proper design and implementation of PUP safety studies will become even more important with the introduction of new molecules, such as extended half-life or human cell-line derived FVIII that propose reduced immunogenicity. Despite these difficulties, carefully performed clinical studies in PUPs may provide important insights into the natural history of the immune response to FVIII and may suggest targets for intervention to reduce immunogenicity.

Assessment of the frequency of regulatory T cells (CD4+CD25+CD127-) in children with hemophilia A: relation to factor VIII inhibitors and disease severity

A rapidly growing evidence showed that regulatory T cells (Tregs) play a crucial role in tolerance to coagulation factors and may be involved in the pathogenesis of inhibitor formation in patients with hemophilia. We determined the percentage of Tregs (CD4CD25CD127) in 45 children with hemophilia A compared with 45 healthy controls, and assessed their relation to the clinical characteristics of patients and factor VIII (FVIII) inhibitors. Patients were studied stressing on frequency of bleeding attacks, joint pain, history of viral hepatitis, and the received therapy (FVIII precipitate/cryotherapy). FVIII activity and FVIII inhibitors were assessed with flow cytometric analysis of CD4CD25CD127 Tregs. According to residual FVIII activity levels, 30 patients (66.7%) had mild/moderate hemophilia A, whereas 15 (33.3%) patients had severe hemophilia A. The frequency of Tregs was significantly lower among all patients with hemophilia A compared with controls (2.59 ± 1.1 versus 3.73 ± 1.12%; P = 0.002). Tregs were significantly decreased among patients with FVIII inhibitors compared with the inhibitor-negative group (P < 0.001). Patients with hematuria or severe hemophilia A had lower Tregs levels than those without (P = 0.34 and P = 0.011, respectively). A significant positive correlation was found between the percentage of Tregs and FVIII among hemophilia A patients. ROC curve analysis revealed that the cut-off value of Tregs at 1.91% could differentiate patients with and without FVIII inhibitors, with a sensitivity of 100% and a specificity of 91.3%. We suggest that alteration in the frequency of Tregs in young patients with hemophilia A may contribute to inhibitor formation and disease severity.

Successful treatment of a noninhibitory antibody-mediated acquired factor X deficiency in a patient with marginal-zone lymphoma

Prolonged clotting times were observed in a patient with spontaneous hemorrhage. Analysis showed severe factor X deficiency due to clearance by a noninhibitory antibody. Lymphadenopathy identified on imaging led to diagnosis of marginal B-cell lymphoma. Treatment of lymphoma with rituximab and chlorambucil resulted in complete disappearance of the bleeding disorder.

Biomimetic biosensor to distinguish between inhibitory and non-inhibitory factor VIII antibodies

Patients with hereditary or acquired haemophilia A may develop inhibitory factor VIII (FVIII) antibodies. These disrupt FVIII activity predominantly by preventing the formation of the tenase complex, leading to a serious bleeding disorder. Antibodies without inhibiting activity, however, can also be found when screening patients with haemophilia A under FVIII supplementation. Therefore, the detection of only these allo- or autoantibodies from plasma is not sufficient. Rather, the characterization of the antibody-induced effects on the coagulation cascade should be considered due to its great diagnostic importance. Currently, inhibitory activities are detected by the functional Bethesda assay, which directly measures the delay in clotting time by the patient plasma. However, this assay does not provide information on the cause of the inhibition. Here, we report the development of a surface plasmon resonance (SPR) biosensor that has the potential to integrate both quantitative and functional information on patient antibody characteristics in one measurement. Recombinant FVIII protein was immobilized on the sensor surface to detect antibodies from patient plasma. The interaction of the FIX- and FXa-clotting proteins with the formed anti-FVIII/FVIII complex could be detected subsequently within the same SPR measurement cycle. Inhibitory antibodies led to the prevention of these interactions. Thus, discrimination between the clinically relevant inhibitory and non-inhibitory antibodies was enabled. In a group of 16 patients with inhibitory antibodies (both ELISA- and Bethesda-positive), 5 patients with non-inhibitory antibodies (ELISA-positive but Bethesda-negative) and 12 healthy controls, diagnostic sensitivity and specificity data of 100% for the FIX interaction were achieved using this biomimetic biosensor approach. The new method allows for detection and quantification, as well as for evaluation of inhibitory activity of allo- and autoantibodies, using small sample volume and short analysis time.

A public health approach to the prevention of inhibitors in hemophilia

The development of an antibody in people with hemophilia to products used in the treatment and prevention of bleeding, also referred to as an inhibitor, is the most serious complication of hemophilia care today. CDC, together with healthcare providers, consumer organizations, hemophilia organizations, and federal partners, has developed a public health agenda to prevent the development of inhibitors. This paper describes a public health approach that combines a national surveillance program with epidemiologic, laboratory, and prevention research to address knowledge gaps in rates and risk factors for inhibitor development, and in knowledge and behaviors of patients and providers, in addition to screening and treatment practices.

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.

Laboratory identification of factor inhibitors: an update

Coagulation factor inhibitors comprise antibodies that bind to and then neutralise specific pro-coagulant plasma proteins. Coagulation factor inhibitors can develop against any coagulation factor, although the most common are against factor VIII (FVIII). These can develop in individuals with inherited haemophilia A (HA) as an immune response to factor replacement therapy, or as auto-antibodies leading to the condition of acquired HA. Clinical suspicion for inhibitors may arise when individuals present with bleeding symptoms without any prior bleeding diathesis, or when a patient with known mild haemophilia presents with a bleeding diathesis more extreme to their usual presentation, or when there is failure of factor replacement therapy to arrest bleeding in a known haemophiliac. The laboratory identification of factor inhibitors requires a careful and systematic approach that excludes other possible causes of prolonged screening tests, most commonly the activated partial thromboplastin time (APTT), and sometimes prothrombin time (PT). Coagulation factor inhibitor studies, including the Bethesda assay, are then undertaken to measure inhibitor titre, which guides treatment. This paper overviews the laboratory investigation of factor inhibitors, and also briefly reviews recent cross-laboratory inhibitor studies and the most recent evidence related to differential inhibitor formation according to type of therapy.

Validation of Nijmegen-Bethesda assay modifications to allow inhibitor measurement during replacement therapy and facilitate inhibitor surveillance

BACKGROUND

As part of a pilot U.S. inhibitor surveillance project initiated at the Centers for Disease Control and Prevention (CDC) in 2006, a centralized inhibitor measurement was instituted.

OBJECTIVE

To validate a modified method for inhibitor measurement suitable for surveillance of treated and untreated patients.

METHODS/RESULTS

In all, 710 subjects with hemophilia A were enrolled; 122 had a history of inhibitor (HI). Nijmegen-Bethesda assay (NBA) results on 50 split specimens shipped on cold packs and frozen were equivalent (r=0.998). Because 55% of 228 initial specimens had factor (F)VIII activity (VIII:C) present, a heat treatment step was added. Heating specimens to 56°C for 30 min and centrifuging removed FVIII, as demonstrated by a reduction of VIII:C and FVIII antigen to <1 U dL(-1) in recently treated patients. Among specimens inhibitor-negative before heating, one of 159 with negative HI and five of 30 with positive HI rose to ≥ 0.5 Nijmegen-Bethesda units (NBU) after heating. Correlation of heated and unheated inhibitor-positive specimens was 0.94 (P=0.0001). The modified method had a coefficient of variation (CV) for a 1 NBU positive control of 10.3% and for the negative control of 9.8%. Based on results on 710 enrollment specimens, a positive CDC inhibitor was defined as ≥ 0.5 NBU. Results were similar when 643 post-enrollment specimens were included. Of 160 enrolled hemophilia B patients, two had HI. All others had NBU ≤ 0.2 at enrollment.

CONCLUSION

The CDC experience demonstrates that this modified NBA can be standardized to be within acceptable limits for clinical tests and can be used for national surveillance.

Development of a new modified Bethesda method for coagulation inhibitors: the Osaka modified Bethesda method

The Nijmegen assay for the factor VIII (F-VIII) inhibitor is recommended by the International Society on Thrombosis and Haemostasis/Scientific and Standardization Committee. However, due to cumbersome and complicated preprocessing, it is presently difficult to introduce this assay into hospital laboratories. We used buffered plasma that was made by addition of 1 volume of 1 mol/l HEPES buffer at pH 7.35 to 9 volumes of plasma to form the test samples. The inhibitor titer was calculated by the remaining rate of F-VIII coagulation activity (F-VIII:C), using the ratio of actual value to the theoretical value. Five hundred microliters of the buffered test plasma and the control (30 mmol/l HEPES buffered saline at pH 7.35) were each mixed with equal volumes (500 μl) of normal pooled plasma in a test tube (11 mm internal diameter and 6.5 ml volume capacity), and incubated at 37°C for 2 h. In our modified Bethesda method, there were no significant changes in pH and F-VIII:C of control and test mixtures after incubation tests for stability. With the modified method, the inhibitor titers (mean, SD) from examining three hemophilia A plasma samples (F-VIII:C, <1-3%) and 40 normal samples (F-VIII:C, 34.5-168.3%) were 0.032, 0.057 and -0.009, 0.057, respectively. By our method, the F-VIII inhibitor titer of type I inhibitor-positive samples was higher than the Nijmegen method, and for type II inhibitor-positive samples, the titer was similar. We believe that our method can be applied to not only the type I inhibitor, but also to assays of type II inhibitor, without cumbersome and complicated preprocessing.

Von Willebrand factor assay proficiency testing. The North American Specialized Coagulation Laboratory Association experience

We evaluated the accuracy and precision of von Willebrand disease (vWD) testing performed by up to 50 North American Specialty Coagulation Laboratories from 2004 through 2009, using proficiency samples from healthy subjects (n = 7) and patients with type 1 vWD (n = 7) or type 2 vWD (n = 3). We analyzed 2,212 submitted results. Precision was highest for von Willebrand factor (vWF) antigen assays (coefficient of variation, 14%), which were performed predominantly by latex immunoassays, and lowest for ristocetin cofactor assays (coefficient of variation, 28%), which were increasingly replaced by collagen binding and immunofunctional methods during the 6-year evaluation period. Overall interpretation error rates ranged from 3% for normal samples, 28% for type 1 vWD, and 60% for type 2 vWD. Type 2 vWD samples were correctly identified by all laboratories using collagen binding/antigen ratios but by only one third of laboratories using ristocetin cofactor/antigen or immunofunctional/antigen ratios. In 2009, only 27% (12/45) of laboratories performed vWF multimer analysis, with error rates ranging from 7% to 22%.