Current laboratory practices in the diagnosis and management of haemophilia: a global assessment

Gene therapy for people with hemophilia B: a proposed care delivery model in Italy

BACKGROUND

Gene therapy is designed to provide people with hemophilia B with a steady and elevated factor (F)IX activity, thereby strengthening protection and relieving the burden of frequent replacement therapy infusions. The European Medicines Agency has approved gene therapy for the severe and moderately severe forms of hemophilia B that uses the FIX-Padua variant (etranacogene dezaparvovec).

OBJECTIVES

The aim was to provide a document dedicated to hemophilia B gene therapy and give a comprehensive overview of the topic.

METHODS

An Italian group of experts in hemophilia carried out a narrative review of the literature and discussed during a virtual meeting several key aspects of the delivery of this treatment in Italy. The discussion covered the organizational model, the role of the multidisciplinary team, the laboratory surveillance, and the patient's journey, from the follow-up to the identification of safety issues and outcome measures.

RESULTS

This article highlights the need to follow the Hub and Spoke organizational model and sheds light on the role of each professional figure within the multidisciplinary teams to favor patient engagement, management, and retention. Moreover, this article stresses the need to perform laboratory tests for patient screening and follow-up and proposes a checklist to help patient identification. Finally, the needs of Italian hemophilia centers have been considered to ensure an efficient implementation of the care delivery model.

CONCLUSION

It is crucial to ensure that centers are appropriately organized, equipped, and trained to adequately select patients, deliver the gene therapy, and perform follow-up.

Field Study and Correlative Studies of Factor IX Variant FIX-R338L in Participants Treated with Fidanacogene Elaparvovec

BACKGROUND

 Fidanacogene elaparvovec, an adeno-associated virus-based gene therapy vector expressing the high-activity factor IX (FIX) variant FIX-R338L, is in development for hemophilia B. One-stage clotting (OS) assays and chromogenic substrate (CS) assays are commonly used to measure FIX-R338L variant activity. Data from ongoing trials suggest FIX activity varies between different OS and CS assays.

MATERIAL AND METHODS

 To better understand FIX-R338L activity in clinical samples, an international multisite field study was conducted across a central laboratory and 18 local laboratories, using standard protocols, reagents, and instrumentation, with individual participant samples from a phase 1/2a study of fidanacogene elaparvovec.

RESULTS

 Unlike the wild-type FIX control, FIX-R338L activity was higher with the OS silica-based assay versus OS ellagic acid-based and CS assays. Variation in FIX activity was greater at the lowest activity levels. Activated FIX (FIXa) in plasma could result in higher OS assay activity or increased thrombin generation, which could overestimate FIX activity. However, FIXa was not detected in the participant samples, indicating that it was not contributing to the OS assay differences. Since individuals on gene therapy may receive exogenous replacement FIX products, replacement products were spiked into patient plasma samples to target a therapeutic concentration. Exogenous FIX was additive to endogenous FIX-R338L, with no interference from FIX-R338L.

CONCLUSION

 These results demonstrate FIX-R338L activity can be measured with OS and CS assays in clinical laboratories and provide insight into assay variability when measuring FIX with endogenously produced FIX-R338L. The findings may help establish best practices for measuring FIX-R338L activity (Clinicaltrials.gov identifier: NCT02484092).

Bioclinical features of haemophilia patients in Benin in 2023: Towards better care

OBJECTIVE

To analyse the demographic, clinical and laboratory data of Beninese patients with haemophilia.

METHOD

A prospective survey was conducted in three different hospitals of Benin from April 2021 to March 2022, to analyse clinical and biological features of patients with haemophilia previously diagnosed or identified based on personal/family history.

RESULTS

A total of 101 patients were studied, 97 with haemophilia A and 4 with haemophilia B, including 26 new cases identified after family investigation. Their median age was 11 years, and the most frequent initial manifestations were cutaneous-mucosal haemorrhages (29.70%) and post-circumcision haemorrhages (25.74%). Previous joint bleedings were present in 77% of them, with an arthropathy in 65 cases, which particularly affected the knees (75%), elbows (41%) and ankles (29%). Factor VIII (FVIII) levels combined with activated partial thromboplastin time (APTT) values did not always enable, as would be expected, the distinction between severe and moderate haemophilia, since they were >1 IU/dl in 31 of 74 patients with APTT > 80 s, and between 1 and 2 IU/dl in 26 other cases with previous joint haemorrhages, including 18 with chronic arthropathy. Therefore, for these patients, severe haemophilia could not be excluded, and this uncertainty probably reflects technical difficulties affecting the pre-analytical and analytical stages of the APTT and FVIII/IX assays.

CONCLUSION

Our study proved that haemophilia is a significant reality in Benin, but also remains under-diagnosed in some districts of the country. In addition, more reliable biological tests are needed in the future to better define the severity of the disease and improve treatment of patients.

Consensus-Based Expert Recommendations on the Management of Hemophilia A in the Gulf Region

BACKGROUND

Hemophilia A presents a significant health challenge in the Gulf region, where it has an especially high prevalence. There are several unmet needs associated with the management of hemophilia A in the region. The aim of this manuscript was to contextualize unmet management needs, provide recommendations to optimize care, and specify requirements for the establishment of gene therapy centers in the region.

SUMMARY

An expert panel was assembled comprising ten clinical hematologists from Kuwait, Oman, Saudi Arabia, and the UAE. The Delphi methodology was used to obtain a consensus on statements relating to several aspects of hemophilia A. A consensus was reached for all statements by means of an online, anonymized voting system. The consensus statements pertain to screening and diagnosis, treatment approaches, and requirements for the implementation of gene therapy.

KEY MESSAGES

There are significant challenges that hinder the optimal management of hemophilia A in the Gulf region. The consensus statements presented provide specific recommendations to improve diagnostic and treatment approaches, promote multidisciplinary care, and optimize regional data generation and reporting. These statements also delineate the requirements for the establishment of gene therapy centers for hemophilia A in the region.

BACKGROUND

Hemophilia A presents a significant health challenge in the Gulf region, where it has an especially high prevalence. There are several unmet needs associated with the management of hemophilia A in the region. The aim of this manuscript was to contextualize unmet management needs, provide recommendations to optimize care, and specify requirements for the establishment of gene therapy centers in the region.

SUMMARY

An expert panel was assembled comprising ten clinical hematologists from Kuwait, Oman, Saudi Arabia, and the UAE. The Delphi methodology was used to obtain a consensus on statements relating to several aspects of hemophilia A. A consensus was reached for all statements by means of an online, anonymized voting system. The consensus statements pertain to screening and diagnosis, treatment approaches, and requirements for the implementation of gene therapy.

KEY MESSAGES

There are significant challenges that hinder the optimal management of hemophilia A in the Gulf region. The consensus statements presented provide specific recommendations to improve diagnostic and treatment approaches, promote multidisciplinary care, and optimize regional data generation and reporting. These statements also delineate the requirements for the establishment of gene therapy centers for hemophilia A in the region.

Treatment changes in hemophilia A with chromogenic factor VIII assay implementation

Background

The one-stage assay (OSA) and the chromogenic assay (CSA) are 2 factor VIII (FVIII) assays used for the diagnosis and classification of hemophilia A. Discrepancies between the 2 assays exist in approximately one-third of patients with mild hemophilia A.

Objectives

The objectives of this study were to report the proportion of patients with mild or moderate hemophilia A and OSA-CSA discrepancies and to report the observed changes in treatment approach prompted by the presence of assay discrepancy. The study aimed to identify OSA:CSA ratio associated with the highest sensitivity for identification of patients in whom modification of treatment approach may be recommended.

Methods

This is a retrospective cohort study including adult (>18-year-old) patients with mild or moderate hemophilia A who were followed up at the Adult British Columbia Hemophilia Program between January 2013 and March 2019.

Results

A total of 75 patients with mild and 23 with moderate hemophilia A based on baseline OSA were included. Overall, 52% of study patients had OSA-CSA discrepancies, and change in treatment approach was observed in 27% of patients with OSA-CSA discrepancy. The OSA:CSA ratio of 1.8 to 3.5 demonstrated the highest area under the receiver operating characteristics curve and sensitivity for identification of patients in which modification of treatment approach may be recommended (AUC 0.75; sensitivity 71%).

Conclusion

In our population, OSA-CSA discrepancy was observed in 52% of patients with mild or moderate hemophilia A, and the treatment approach in 27% of these patients had to be modified.

Methods for anti-factor VIII antibody levels in haemophilia A patients - validation of a multiplex immunoassay and comparability with assays measuring non-neutralising and neutralising antibodies (inhibitors)

INTRODUCTION

The development of neutralising (inhibitors) and non-neutralising antibodies (NNAs) is a complication to factor replacement therapy in haemophilia. The diagnostic methods available lack standardisation, have high inter-laboratory variation, and false-negative as well as false-positive results may affect treatment. Both functional inhibitors and NNAs may be detected with higher reproducibility, sensitivity and specificity using the immunological Luminex xMAP-based fluorescence-immunoassay (xFLI).

AIM

Validation of our xFLI and comparability with enzyme-linked immunosorbent assay (ELISA) and chromogenic Nijmegen-Bethesda assay (CBA) for anti-FVIII antibodies in haemophilia A (HA) patients.

METHODS

The xFLI method was developed with full-length and B-domain deleted factor coupled to magnetic beads, optimised and validated for performance characteristics. Comparability with ELISA and CBA was evaluated in HA patient samples (n = 112), serial samples in six inhibitor patients and reference interval and decision-limits in healthy donors (n = 44).

RESULTS

The intra- and inter-assay precision (CV%) for the xFLI method was below 6% and detection limit (LLOQ) .084 ng/mL (NovoEight). All ELISA-positive samples were positive with either Advate or NovoEight. Additionally, 10.7%-14.3% were xFLI-positive and ELISA-negative. All but one CBA-positive sample was above 3SD with xFLI; one was between 2 and 3SD. 29.1% were xFLI-positive and CBA negative. The overall concordance between xFLI and ELISA was 82.1% and xFLI and CBA 77.9%.

CONCLUSION

The anti-FVIII antibody xFLI method is adaptable to clinical practice and more sensitive and reproducible than ELISA and CBA. Actual NNA titers are determined to both full-length and B-domain deleted FVIII. The xFLI is thus valuable for confirmation of all anti-FVIII antibodies.

Factor IX inhibitors in haemophilia B: A report of National Haemophilia Registry in China

INTRODUCTION

The development of inhibitors against factor FIX (FIX) is the most serious complication of FIX replacement therapy in haemophilia B (HB) patients. Currently, only few cohorts of HB inhibitor patients have been reported worldwide.

AIM

This Chinese nationwide study of HB inhibitor patients explored their risk factors for FIX inhibitor development and experience on their management.

METHODS

We retrospectively analysed patient characteristics, F9 genotypes, treatment strategies and outcomes of HB inhibitor patients registered to the Chinese National Registry and Patient Organization Registry.

RESULTS

Forty-four unique HB inhibitor patients were identified in 4485 unique HB patients registered by year 2021 to the two Registries. Inhibitor diagnosis were usually delayed and the low prevalence (.98%) may suggest some inhibitor patients were not identified. Their median age at inhibitor diagnosis was 7.5 (IQR, 3.0-14.8) years. Most patients (95.5%) had high-titre inhibitors. Allergic/Anaphylactic reactions occurred in 59.1% patients. Large deletions and nonsense mutations were the most common F9 mutation types in our FIX inhibitor patients. Patients with large F9 gene deletions were more likely to develop inhibitors (p = .0002), while those with missense mutations had a low risk (p < .0001). Thirteen (29.5%) patients received immune tolerance induction (ITI) therapy using low-dose prothrombin complex concentrate regimens. Twelve completed ITI with three (25.0%) achieving success. Nephrotic syndrome developed in two (16.7%) patients during ITI.

CONCLUSION

This study reports the largest Chinese cohort of HB inhibitor patients. Large deletions were most significantly associated with inhibitor development. Low-dose ITI might be feasible for FIX inhibitor eradication.

Optimization and evaluation of a two-stage chromogenic assay procedure for measurement of emicizumab plasma levels

Emicizumab mimics the hemostatic activity of activated factor VIII (FVIIIa) within the tenase complex. Despite functional similarities between FVIIIa and emicizumab, conventional laboratory methods designed for monitoring of FVIII activity are inappropriate for the measurement of emicizumab. At present, a modified one stage (FVIII) assay (mOSA) is mainly used for emicizumab monitoring. Two-stage chromogenic FVIII assays based on human factors can be used, although limited performance due to lack of corresponding optimization might be observed. Furthermore, the presence of FVIII or anticoagulants in the patient sample may falsify assay results. To address these issues, we optimized and evaluated a two-stage chromogenic assay (emi-tenase) for measurement of emicizumab in plasma samples. Heat inactivation of samples was established to abolish the influence of endogenous or substituted FVIII. The lower limit of quantification (LLoQ) was found to be 2 μg/ml in a manual assay format and 9.5 μg/ml on an automated coagulation analyzer. Intra- and inter-assay coefficients of variation (CV) did not exceed 20%. Analysis of 17 patient plasma samples with severe haemophilia A under emicizumab treatment showed good correlation of results between the emi-tenase assay and the mOSA (Cohens Kappa coefficient = 0.9). Taken together, the emi-tenase assay allows specific measurement of emicizumab plasma levels over a broad concentration range (10 μg/ml to 100 μg/ml). The assay can be applied on an automated coagulation analyzer, demonstrating its applicability within a routine laboratory setting.

International consensus recommendations on the management of people with haemophilia B

Haemophilia B is a rare X-linked genetic deficiency of coagulation factor IX (FIX) that, if untreated, can cause recurrent and disabling bleeding, potentially leading to severe arthropathy and/or life-threatening haemorrhage. Recent decades have brought significant improvements in haemophilia B management, including the advent of recombinant FIX and extended half-life FIX. This therapeutic landscape continues to evolve with several non-factor replacement therapies and gene therapies under investigation. Given the rarity of haemophilia B, the evidence base and clinical experience on which to establish clinical guidelines are relatively sparse and are further challenged by features that are distinct from haemophilia A, precluding extrapolation of existing haemophilia A guidelines. Due to the paucity of formal haemophilia B-specific clinical guidance, an international Author Group was convened to develop a clinical practice framework. The group comprised 15 haematology specialists from Europe, Australia, Japan, Latin America and North America, covering adult and paediatric haematology, laboratory medicine and biomedical science. A hybrid approach combining a systematic review of haemophilia B literature with discussion of clinical experience utilized a modified Delphi format to develop a comprehensive set of clinical recommendations. This approach resulted in 29 recommendations for the clinical management of haemophilia B across five topics, including product treatment choice, therapeutic agent laboratory monitoring, pharmacokinetics considerations, inhibitor management and preparing for gene therapy. It is anticipated that this clinical practice framework will complement existing guidelines in the management of people with haemophilia B in routine clinical practice and could be adapted and applied across different regions and countries.

External quality assessment for one-stage and chromogenic factor IX assays in samples containing Alprolix (rFIXFc) or Idelvion (rIX-FP) and evidence that UK National External Quality Assessment Scheme for blood coagulation samples are commutable with patient samples

INTRODUCTION

There may be clinically relevant differences between results of different FIX assays in samples containing extended half life FIX concentrates requiring regular surveillance of assay results through proficiency testing exercises. Control materials used in proficiency testing must be commutable, that is have the same inter-assay properties as those demonstrated by authentic clinical samples when measured by different analytical methods.

METHODS

We assessed relationships between results with different FIX assays and commutability of UK National External Quality Assessment Scheme (NEQAS) materials containing rIX-FP (Idelvion) or rFIXFc (Alprolix) by comparing results obtained using widely used one-stage and chromogenic assays during a proficiency testing exercise with results obtained when analysing a series of individual patient samples using the same assay systems. NEQAS samples prepared by addition of either Idelvion or Alprolix to FIX deficient plasma were sent to 76 haemophilia centres in Europe. A total of 18 Idelvion and 22 Alprolix patient samples were assayed in a single centre. Two chromogenic and two one-stage assays were compared.

RESULTS

The pattern of results obtained for NEQAS samples and patient samples was similar. In all cases, the NEQAS sample data point was within the scatter of patient sample data in plots of patient sample results showing one-stage assay results using Synthasil or Actin FS plotted against chromogenic assay results with Biophen or Rox chromogenic FIX kits.

CONCLUSION

This indicates that the NEQAS samples containing Idelvion or Alprolix were commutable and therefore suitable for use in proficiency testing exercises.

Genetic and Bioinformatic Strategies to Improve Diagnosis in Three Inherited Bleeding Disorders in Bogotá, Colombia

Inherited bleeding disorders (IBDs) are the most frequent congenital diseases in the Colombian population; three of them are hemophilia A (HA), hemophilia B (HB), and von Willebrand Disease (VWD). Currently, diagnosis relies on multiple clinical laboratory assays to assign a phenotype. Due to the lack of accessibility to these tests, patients can receive an incomplete diagnosis. In these cases, genetic studies reinforce the clinical diagnosis. The present study characterized the molecular genetic basis of 11 HA, three HB, and five VWD patients by sequencing the F8, F9, or the VWF gene. Twelve variations were found in HA patients, four in HB patients, and 19 in WVD patients. From these variations a total of 25 novel variations were found. Disease-causing variations were used as positive controls for validation of the high-resolution melting (HRM) variant-scanning technique. This approach is a low-cost genetic diagnostic method proposed to be incorporated in developing countries. For the data analysis, we developed an accessible open-source code in Python that improves HRM data analysis with better sensitivity of 95% and without bias when using different HRM equipment and software. Analysis of amplicons with a length greater than 300 bp can be performed by implementing an analysis by denaturation domains.

Guidance for establishing a factor VIII testing protocol for the myriad of factor VIII products

INTRODUCTION

Management of hemophilia A has changed significantly in the past few years with the expansion of new and/or modified products as treatment options. Unfortunately, many of the standard factor VIII assays do not always accurately measure all available treatment products; therefore, the laboratory must investigate various assay algorithms to ensure the reporting of the correct results.

METHODS

Requirements for factor testing, diagnosis and severity levels, product testing, factor VIII inhibitor detection and titers, are evaluated, and potential algorithms are created for optimal assessment of patients with hemophilia A.

RESULTS

The potential for inaccurate result reporting for patients with hemophilia A or those being treated with the myriad of products has left many laboratories uncertain as to which assay algorithm to implement to ensure reporting the correct results for all products used in their hemophilia program. Algorithms for using either One-stage Clotting assays or Chromogenic assays or a combination of both types of assays are presented for each laboratory to implement based on their clinical situation.

CONCLUSIONS

Several algorithms are considered based on the needs of the clinical providers and their patients. Each laboratory must select a testing algorithm that is cost-effective and within available resources, yet that encompasses the needs of their providers and patients. Laboratory personnel must consider all assay uses (factor VIII levels, different products, interfering products, and inhibitor titers) in determining the best algorithm for their laboratory. This paper is a starting guide for developing the best factor VIII testing assays and protocols for your laboratory.

Hemophilia A (Factor VIII Deficiency)

Remarkable changes are occurring in the diagnosis and management of individuals with hemophilia A. Genetic testing, including next-generation sequencing, enables family planning, carrier testing, and prenatal diagnosis. Musculoskeletal ultrasound examination facilitates the early detection of acute bleeds and joint disease in clinic, enabling more rapid bleed resolution and treatment planning. Novel therapies offer simpler weekly or monthly administration, some by subcutaneous injection, with better compliance and quality of life, as well as fewer bleeds. Gene therapy provides a 1-time phenotypic "cure" that is cost effective, but may be complicated by waning levels, vector immune responses, and hepatotoxicity.

Measuring factor VIII activity in samples from patients treated with N8-GP (Esperoct® ; turoctocog alfa pegol) during the pathfinder clinical trials programme

FVIII activity in samples taken at various time points from 21 patients treated with N8-GP (Esperoct^® ; turoctocog alfa pegol) during the pathfinder clinical trial programme was assessed and compared using different assay methods. FVIII activity measurements in samples from patients treated with N8-GP were similar using chromogenic assays, regardless of calibration method or kit/analyser combination. FVIII activity measurements using one-stage aPTT-based assays were slightly lower when calibrated using normal human plasma (NHP) compared with a product-specific standard; this difference may be partially attributable to differences in the aPTT reagent/analyser combinations used to perform the measurements. Overall, these results confirm the accuracy of FVIII activity measurements using N8-GP-treated patient samples and routine clinical laboratory methods with NHP calibration.

Development of a Self-Assessment Tool for the Nontechnical Skills of Hemophilia Teams

BACKGROUND AND OBJECTIVES

The treatment of chronic illnesses requires health care professionals (HCPs) to master several nontechnical skills to meet patient care needs. This article aims to describe the rationale and the inductive process through which a self-assessment tool for the nontechnical skills of hemophilia teams was conceived, developed, and tested.

METHODS

Starting from an explorative analysis of hemophilia HCP work experiences, the process followed 3 phases: an in-depth analysis of hemophilia HCP skills; the questionnaire development; and a pilot study.

RESULTS

Using the voice of HCPs as a starting point, the tool proved to be able to identify precise cross-professional and intercultural challenges as well as related required and/or acquired skills in the hemophilia field.

CONCLUSION

The proposed tool may contribute to providing HCPs with strategic knowledge to successfully perform everyday practices, to improve the effectiveness of hemophilia teams and the care model adopted by their centers, and to implement intercultural research in this field. It may be used to propose ad hoc training courses targeted by challenge, in order to fill the major gaps reported by the teams, or targeted by medical specialty or country (and therefore health care system) specificity.

The traceability of commercial plasma calibrators to the plasma International Standards for factor VIII and factor IX

Accurate measurement of coagulation factors is essential, especially for diagnosis of deficiency. Clinical laboratories use commercially available plasma calibrators, which should be traceable to the relevant plasma International Standard (IS). This study assessed the relationship between the plasma IS for factors IX (FIX) and VIII (FVIII) and some commonly used commercial calibrators. Calibrators from seven manufacturers were assayed for FIX and FVIII activity by one‐stage clotting assay (OSCA) using different activated partial thromboplastin time (APTT) reagents and deficient plasmas, or chromogenic assay (CA). Results were calculated relative to the 4th IS Factors II,VII,IX,X, Plasma or the 6th IS Factor VIII/VWF, Plasma. Results for each calibrator were similar across the APTT reagents and deficient plasmas used. All calibrators showed a recovery of 90%‐111% of the manufacturers’ values, except calibrator C, which had recovery of around 85%. CA gave similar results, with good recovery for all but calibrator C. Similar low recoveries for OSCA and CA were found for a different lot of calibrator C and for a different calibrator product from manufacturer C. When all calibrators from manufacturer C were assayed by OSCA using the manufacturer's own deficient plasmas and APTT reagents, the mean recovery was still below 90%. Overall, there was good traceability of the international unit between the IS and commercial calibrator plasmas. Calibrators from one manufacturer consistently yielded lower than expected values for FIX and FVIII. This could lead to an over‐estimation of the coagulation factor content in patient samples and demonstrates the importance of careful choice of calibrator.

Factor VIII and IX assays for post-infusion monitoring in hemophilia patients: Guidelines from the French BIMHO group (GFHT)

Replacement therapy with plasma-derived or recombinant FVIII and FIX (pdFVIII/pdFIX or rFVIII/rFIX) concentrates is the standard of treatment in patients with haemophilia A and B, respectively. Measurement of factor VIII (FVIII:C) or factor IX (FIX:C) levels can be done by one-stage clotting assay (OSA) or chromogenic substrate assay (CSA). The French study group on the Biology of Hemorrhagic Diseases (a collaborative group of the GFHT and MHEMO network) presents a literature review and proposals for the monitoring of FVIII:C and FIX:C levels in treated haemophilia A and B patients, respectively. The use of CSA is recommended for the monitoring of patients treated with pdFVIII or rFVIII including extended half-life (EHL) rFVIII. Except for rFVIII-Fc, great caution is required when measuring FVIII:C levels by OSA in patients substituted by EHL-rFVIII. The OSA is recommended for the monitoring of patients treated with pdFIX or rFIX. Large discordances in the FIX:C levels measured for extended half-life rFIX (EHL-rFIX), depending on the method and reagents used, must lead to great attention when OSA is used for measuring FIX:C levels in patients substituted by EHL-rFIX. Data of most of recent studies, obtained with spiked plasmas, deserve to be confirmed in plasma samples of treated patients.

An overview of turoctocog alfa pegol (N8-GP; ESPEROCT® ) assay performance: Implications for postadministration monitoring

Factor replacement therapy with factor VIII (FVIII) concentrates is the current standard of care for patients with haemophilia A. Postadministration monitoring of FVIII activity during on‐demand or prophylactic treatment is important, for example to guide a suitable dosing regimen. While the use of two‐stage chromogenic substrate (CS) assays is increasing, activated partial thromboplastin time (APTT)‐based one‐stage clotting (OSC) assays are most commonly used to measure FVIII activity in clinical laboratories. Substantial variations in activity measurements have been observed in association with some OSC assay reagents when assessing extended half‐life FVIII molecules. Certain silica‐based APTT reagents have previously been shown to underestimate FVIII activity with the polyethylene glycol (PEG)‐conjugated product turoctocog alfa pegol (N8‐GP [ESPEROCT^®]; Novo Nordisk A/S). As a wide range of assay reagents are used in clinical laboratories worldwide, it is essential to establish which can be used to accurately measure activity with modified FVIII concentrates. Here, we describe the approach taken by Novo Nordisk to determine the suitability and accuracy of assays and reagents to measure FVIII activity in samples that contain N8‐GP. While accurate activity measurements were possible with all tested CS assays and most of the OSC APTT reagents tested, three APTT reagents that contain silica as a contact activator were found to underestimate N8‐GP recovery (APTT‐SP, TriniCLOT™, STA^® PTT‐Automate). The data demonstrate the importance of characterizing the accuracy of each FVIII activity assay. Any limitations should be communicated to treating physicians and the clinical laboratories that test samples containing N8‐GP.

Clinical utility and impact of the use of the chromogenic vs one-stage factor activity assays in haemophilia A and B

Treatment of haemophilia A/B patients comprises factor VIII (FVIII) or factor IX (FIX) concentrate replacement therapy, respectively. FVIII and FIX activity levels can be measured in clinical laboratories using one‐stage activated partial thromboplastin time (aPTT)‐based clotting or two‐stage chromogenic factor activity assays. We discuss strengths and limitations of these assays, providing examples of clinical scenarios to highlight some of the challenges associated with their current use for diagnostic and monitoring purposes. Substantial inter‐laboratory variability has been reported for one‐stage assays when measuring the activity of factor replacement products due to the wide range of currently available aPTT reagents, calibration standards, factor‐deficient plasmas, assay conditions and instruments. Chromogenic activity assays may avoid some limitations associated with one‐stage assays, but their regulatory status, perceived higher cost, and lack of laboratory expertise may influence their use. Haemophilia management guidelines recommend the differential application of one or both assays for initial diagnosis and disease severity characterisation, post‐infusion monitoring and replacement factor potency labelling. Efficient communication between clinical and laboratory staff is crucial to ensure application of the most appropriate assay to each clinical situation, correct interpretation of assay results and, ultimately, accurate diagnosis and optimal and safe treatment of haemophilia A or B patients.

Evaluation of N8-GP Activity Using a One-Stage Clotting Assay: A Single-Center Experience

N8-GP (ESPEROCT®; turoctocog alfa pegol; Novo Nordisk A/S, Bagsvaerd, Denmark) is an extended half-life recombinant factor VIII (FVIII) molecule. FVIII-deficient plasma spiked with N8-GP can be accurately measured using many activated partial thromboplastin time (aPTT)-based one-stage clotting assay reagents with normal human plasma calibrators. To date, there are few data on the measurement accuracy of samples from patients treated with N8-GP. Here, we measure patient samples during routine treatment monitoring. Three previously treated patients with severe hemophilia A (HA) without inhibitors (baseline FVIII activity <0.01 IU/mL) received 50 IU/kg N8-GP every fourth day or twice weekly over 5 years as part of the pathfinder2 trial. Patient samples were monitored using the Pathromtin® SL aPTT reagent (Siemens Healthcare GmbH, Erlangen, Germany), a BCS® XP System analyzer (Siemens), and Standard Human Plasma (Siemens) or product-specific calibrators. Patient age ranged from 36 to 62 years. Overall, measurements performed using product-specific or Standard Human Plasma calibrators were in good agreement, with ratios randomly distributed around 1.0. Peak ratios tended to be closer to 1.0 than trough samples. Pathromtin® SL with Standard Human Plasma calibrator consistently and accurately measured FVIII activity in samples from severe HA patients receiving N8-GP prophylaxis.

A cost-effective approach to factor assay calibration using a truncated live calibration curve

INTRODUCTION

The measurements of clotting factor activities are usually performed using a one-stage clotting assay (OSA) or chromogenic substrate assay (CSA). Advances in automated coagulation analysers have led to the utilization of stored calibration curves. There are sometimes substantial intervals between test calibration and analysis of samples. Variability in results can be influenced by calibrant and methodology. Several guidelines recommend calibration and patient samples be performed together in parallel; this incurs costs, but reliance on a stored calibration curve may lead to inaccuracy of results over time.

METHODS

We evaluated inclusion of a live truncated (3 point) calibration curve using calibrator plasma alongside test samples and compared results calculated against the stored calibration curves and live truncated calibration to assess the impact on precision and accuracy. The feasibility of this was tested on two hospital sites in the UK; OSA and CSA were performed on Sysmex CS5100 using Actin FS, SynthASil, Innovin, Biophen chromogenic VIII and Rossix chromogenic IX.

RESULTS

Results of two batches of IQC were compared for FII, FV, FVII, FX, FIX:C, FXI, FXII and OSA FVIII (FVIII:C1) and CSA FVIII:C (FVIII:CR) and FXI:C. By utilizing a live truncated calibration, precision improved with the most striking examples: FXII %CV 23.1% to 3.1% (site A) FXI 7.3% to 2.4% (site B). The improvement in other clotting factors was more modest.

CONCLUSION

To the best of our knowledge, this is the first study that demonstrates that the use of a live truncated calibration curve will improve precision and accuracy.

A field study evaluating the activity of N8-GP in spiked plasma samples at clinical haemostasis laboratories

AIM

N8-GP (turoctocog alfa pegol) is a glycoPEGylated, extended half-life human recombinant factor VIII (FVIII) shown to be an efficacious treatment for patients with haemophilia A. Accurate monitoring of replacement therapy helps ensure proper dosing, leading to better patient care. The objective of this field study was to evaluate the accuracy and intra- and inter-laboratory variabilities of N8-GP and rAHF (Advate^® ) FVIII activity (FVIII:C) measurements in clinical laboratories using their routine methods and reagents.

METHODS

Laboratories measured plasma samples spiked with 0.03, 0.2, 0.6 and 0.9 IU/mL N8-GP or rAHF. Samples were blinded, and laboratories were instructed to perform evaluations using their routine FVIII activity assays and calibrators.

RESULTS

Of the 67 participating laboratories from 25 countries, 60 used a one-stage assay, 36 used a chromogenic assay, and 29 used both one-stage and chromogenic assays. Participating laboratories used nine different activated partial thromboplastin time (aPTT) reagents, the most common being SynthASil^® and Actin^® FS. Most aPTT reagents recovered N8-GP close to target. Three silica-based aPTT reagents (APTT-SP, TriniCLOT™ and STA^® PTT-Automate) underestimated N8-GP, recovering 40%-83% of target concentration. For chromogenic assays, N8-GP and rAHF recoveries were comparable at all concentrations, with overall mean recoveries for both products close to 130%. Assay variability was similar for both assay types and both products; inter-laboratory variability was greater than intra-laboratory variability and highest at 0.03 IU/mL.

CONCLUSIONS

Most clinical laboratories accurately measured N8-GP and rAHF when using their in-house one-stage or chromogenic FVIII:C assays. However, three silica-based aPTT reagents underestimated N8-GP recovery.

Intrinsic differences between FVIIIa mimetic bispecific antibodies and FVIII prevent assignment of FVIII-equivalence

Essentials Non-factor VIII (FVIII) therapies for hemophilia A, such as bispecific antibodies (bsAbs), are in development. Bispecific antibodies are intrinsically different from FVIII and lack many of the same regulatory mechanisms. These differences complicate assignment and interpretation of FVIII-equivalent activity. Inability to assign FVIII equivalence compromises our capacity to assess hemostatic potential of bsAb therapies.

BACKGROUND

Activated factor VIII (FVIIIa) mimetic bsAbs aim to enable prophylactic treatment of hemophilia A patients with and without inhibitors. With different mechanisms of action, benchmarking their activity against FVIII to determine efficacious yet safe dosage is difficult.

OBJECTIVE

To compare the activities of sequence identical emicizumab (SI-Emi) and another bsAb, BS-027125, to recombinant FVIII (rFVIII) using clinical and nonclinical assays and to evaluate our ability to assign a FVIII-equivalent value to bsAbs and implications thereof.

METHODS

Activities of SI-Emi, BS-027125, and rFVIII were measured by one-stage clotting assay, chromogenic factor Xa generation assay, and thrombin generation assay. We also assessed the activity of anti-FIXa and anti-FX bivalent homodimers of each bsAb and probed the effect of different reagents in thrombin generation assay (TGA).

RESULTS

The FVIII-like activity of SI-Emi and BS-027125 ranged greatly across each assay, varying both by parameter measured within an assay and by reagents used. Notably, SI-Emi anti-FIXa bivalent homodimer had meaningful activity in several assays, whereas BS-027125 anti-FIXa bivalent homodimer only had activity in the chromogenic assay. Surprisingly, SI-Emi displayed activity in the absence of phospholipids, while BS-027125 had minimal phospholipid-independent activity.

CONCLUSIONS

Bispecific antibodies demonstrate little consistency between assays tested here owing to intrinsic differences between FVIII and bsAbs. While some trends are shared, the bsAbs also differ in mechanism. These inconsistencies complicate assignment of FVIII-equivalent values to bsAbs. Ultimately, a deeper mechanistic understanding of bsAbs as well as bsAb-tailored assays are needed to monitor and predict their hemostatic potential and long-term efficacy and safety confidently.

Laboratory assay measurement of modified clotting factor concentrates: a review of the literature and recommendations for practice

Over the past several years, novel modified clotting factor concentrates (CFCs) have been introduced into practice and are now widely prescribed in the countries where they are licensed. These products allow for less frequent infusions of CFC, thereby providing improved convenience and/or higher trough levels. They have been extensively studied for prophylaxis, episodic treatment of bleeding and for surgical prophylaxis. One issue that has emerged regarding the clinical application of these products revolves around the measurement of infused CFC in the clinical coagulation laboratory. Recent studies have demonstrated significant problems with the measurement of correct FVIII/IX levels following infusion of novel CF VIII/IX concentrates. The source of this problem appears to be related to the tremendous variability of the APTT reagents that are used in the one-stage clotting assay, the most commonly used assay for determining factor levels. More specifically, the issue is related to the type of activator used in the reagents. Depending on the combination of the CFC and the APTT activator, the observed results may be either under- or overestimated to degrees that would be clinically relevant. Recommendations based on a review of published information regarding the potential for incorrect measurements of factor VIII/IX levels following infusion of recently developed, novel factor VIII/IX CFCs are presented for the clinician to use in clinical practice.

Performance of a recombinant fusion protein linking coagulation factor IX with recombinant albumin in one-stage clotting assays

Essentials Performance of the one-stage clotting (OSC) assay varies with the clotting activator used. Recombinant FIX-albumin fusion protein (rIX-FP) was reliably monitored with most OSC reagents. rIX-FP shows comparable reagent-dependent variability to other rFIX products in the OSC assay. Actin® FS and kaolin-based reagents underestimated rIX-FP activity by around 50% in the OSC assay. SUMMARY: Background Measuring factor IX activity (FIX:C) with one-stage clotting (OSC) assays, based on the activated partial thromboplastin time (APTT), is the current mainstay of diagnostic techniques for hemophilia B. Assessing the performance of new recombinant FIX (rFIX) products in OSC assays is essential, as APTT reagents from different manufacturers yield different potency estimates for rFIX. Objectives To evaluate the extent to which choice of reagent composition influences rFIX potency measurements of recombinant FIX-albumin fusion protein (rIX-FP, IDELVION) activity in OSC assays. Methods rIX-FP was added to FIX-deficient plasma, and FIX:C was assessed centrally and locally in a multicenter international field study with a variety of commercial OSC APTT reagents. Paired sample analysis of clinical samples was performed to compare values of FIX:C from local and central laboratories. In-house bioanalytical investigations with spiked samples were conducted to compare the APTT-reagent dependent variability of rIX-FP with unmodified rFIX and rFIX Fc fusion protein (rFIXFc). Results Central and local assessments of FIX:C from 10 countries and 21 participating centers showed comparable results to those from the central laboratory across the majority of 18 different APTT reagents from both clinical and spiked samples. There was a consistent underestimation of rIX-FP activity of ≈ 50% with OSC assays using Actin FS or kaolin-based APTT reagents. In the bioanalytical study, rIX-FP showed comparable variability in OSC assays to unmodified rFIX and rFIXFc. Conclusions rIX-FP activity can be accurately measured by the use of OSC assays with the majority of commercial reagents. Actin FS or kaolin-based reagents will probably lead to a 50% underestimation of activity.

Reagent-specific underestimation of turoctocog alfa pegol (N8-GP) clotting activity owing to decelerated activation by thrombin

BACKGROUND

Factor VIII (FVIII) procoagulant activity is commonly assessed by measuring the activated partial thromboplastin time (APTT) to clot formation using one of the many available but differently composed reagents. The majority of APTT reagents also accurately recover the activity of the extended half-life molecule N-glycoPEGylated FVIII (N8-GP; turoctocog alfa pegol), while a few silica-based reagents give a low recovery.

OBJECTIVE

To identify the cause of N8-GP activity underestimation in the presence of certain silica-based APTT reagents.

METHODS

Development of FVIIIa-dependent tenase activity and appearance of FVIIIa from N8-GP and its non-PEGylated counterpart (N8) were compared using clotting assays, a factor Xa (FXa) activity assay mimic thereof, and thrombin activation time courses.

RESULTS

A strong correlation was demonstrated between clotting and FXa activity assays based on similar recoveries of N8-GP activity and equal responses to an altered duration of the contact activation phase, validating the latter as a useful clotting assay mimic. Contact activation phase duration influenced, and could even eliminate, N8-GP activity underestimation. Thrombin-catalyzed conversion of N8-GP to FVIIIa was considerably slower than that of N8 despite similar extents of adsorption to silica particles in APTT-SP, suggesting different modes and/or orientations of adsorption.

CONCLUSIONS

Some contact activators reduce thrombin's ability to cleave N8-GP more than native FVIII. Decelerated thrombin activation of N8-GP is reflected in delayed FVIIIa-dependent appearance of FXa activity in plasma, in turn leading to prolonged clotting time. This forms the basis for underestimation of N8-GP activity as measured by one-stage clotting assay against a FVIII standard.

Analytical variation in factor VIII one-stage and chromogenic assays: Experiences from the ECAT external quality assessment programme

Background

Both one‐stage (OSA) and chromogenic substrate assays (CSA) are used to measure factor VIII (FVIII) activity. Factors explaining analytical variation in FVIII activity levels are still to be completely elucidated.

Aim

The aim of this study was to investigate and quantify the analytical variation in OSA and CSA.

Methods

Factors determining analytical variation were studied in sixteen lyophilized plasma samples (FVIII activity <0.01‐1.94 IU/mL) and distributed by the ECAT surveys. To elucidate the causes of OSA variation, we exchanged deficient plasma between three company set‐ups.

Results

On average, 206 (range 164‐230) laboratories used the OSA to measure FVIII activity and 30 (range 12‐51) used CSA. The coefficient of variation of OSA and CSA increased with lower FVIII levels (FVIII <0.05 IU/mL). This resulted in misclassification of a severe haemophilia A sample into a moderate or mild haemophilia A sample in 4/30 (13.3%) of CSA measurements, while this was 37/139 (26.6%) for OSA. OSA measurements performed with reagents and equipment from Werfen showed slightly lower FVIII activity (0.93, IQR 0.88‐0.98 IU/mL) compared to measurements with Stago (1.07, IQR 1.02‐1.14 IU/mL) and Siemens (1.03, IQR 0.97‐1.07 IU/mL). Part of this difference is explained by the value of the calibrator. For CSA, the measured FVIII levels were similar using the different kits.

Conclusions

In the lower range (<0.05 IU/mL), analytical variation of FVIII measurements is high in both OSA and CSA measurements. The variation in FVIII activity levels was partly explained by specific manufacturers. Further standardization of FVIII measurements and understanding of analytical variation is required.

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.

Postanalytical considerations that may improve the diagnosis or exclusion of haemophilia and von Willebrand disease

von Willebrand disease (VWD) and haemophilia represent the most common inherited or acquired bleeding disorders. However, many laboratories and clinicians may be challenged by their accurate diagnosis or exclusion. Difficulties in diagnosis/exclusion may include analytical issues, where assays occasionally generate an incorrect result (ie representing an analytical error) or have limitations in their measurement range of and/or low analytical sensitivity. Also increasingly recognized is the influence of preanalytical issues on the diagnosis of VWD or haemophilia. Unfortunately, postanalytical considerations are often not well considered in the diagnostic process. Therefore, this narrative review aims to provide an overview of some important postanalytical considerations that may help improve the diagnosis of VWD and haemophilia. This review primarily discusses aspects around reporting of test results. However, we also discuss other less well-recognized postanalytical considerations, including the use of assay ratios to help identify differential diagnoses and then guide further investigation.

A survey of characteristics and current educational needs of hemophilia treatment centers within Asia Pacific

BACKGROUND

Poor disease understanding and gaps in expertise regarding hemophilia care have been identified at all levels in Asia Pacific. Continued education for involved healthcare professionals (HCPs) is crucial for improved delivery.

OBJECTIVES

To identify training and educational needs of hemophilia HCPs in Asia Pacific.

METHODS

Clinicians working at hemophilia treatment centers (HTCs), identified from the World Federation of Hemophilia Directory, were contacted by the Asia Pacific Hemophilia Working Group (APHWG). An electronic survey was sent to 161 centers from 15 countries for which HTC identification was complete to assess HTC characteristics, educational status, and needs. Responses were stratified by national economic capacity.

RESULTS

From March 23 to June 6, 2016, clinicians from 58 HTCs completed the survey. Most reported availability of specialists to serve core patient requirements, although availability of trained nurses and geneticists was low in lower-middle income countries (LMICs). Although 98.3% of HTCs had laboratory facilities, 8.8% do not participate in any quality assessment schemes. The most common limitations of current initiatives were infrequency and lack of local language content. Education is currently mostly received via internet, particularly among LMICs and upper-middle income countries (UMICs), though there is strong preference for meetings. Main barriers to receiving education were funding and time constraints. Unique priority topics were musculoskeletal management, quality of life and management by non-hematologists (high-income countries), inhibitor management and research (UMICs), and outcomes assessment (LMICs).

CONCLUSION

In Asia Pacific, training programs should be tailored according to unique needs of differing economic capacities and resource settings.

Educational needs of hematologists and laboratory professionals regarding factor activity assays

Introduction

Diagnosis and management of hemophilia require accurate and precise measurements of factor activity levels. Activity is traditionally measured via one-stage (OS) clot-based assay; however, chromogenic substrate (CS) assays may be needed for certain cases. A survey was performed to understand assay-related knowledge gaps among hematologists and laboratory professionals.

Methods

Separate web-based surveys were administered to hematologists who manage hemophilia and to laboratory professionals and queried practice patterns, knowledge of/attitudes toward CS assays, and interest in continuing education.

Results

A total of 51 hematologists participated in this study; 67% managed hemophilia patients for ≥10 years and 24% were affiliated with a hemophilia treatment center (HTC). Most (80%) stated familiarity with general assay interpretation. Majorities of non-HTC and HTC respondents agreed that CS assays are more accurate than OS assays (62%/67%), although non-HTC hematologists indicated less understanding of when to order a CS assay (49%/67%). Fewer non-HTC respondents expressed concerns regarding the reliability of OS assays for diagnosis (38%/67%) and monitoring (38%/75%). Most (80%) expressed an interest in factor assay education, especially on available assays, efficacy, and best practices (39%). A total of 57 laboratory professionals participated, averaging 10 years in their current position; most (88%) were hospital based. More performed OS (72%) than CS (10%) or both (17%) assays; only 11% reported confidence with the interpretation of CS results. Few expressed concerns regarding the reliability of OS for diagnosis (9%) or monitoring (12%). Reported barriers to CS use included infrequent need (68%), lack of US Food and Drug Administration (FDA) approval (61%), and need for validation work (56%). Most (70%) were interested in CS assay education; top interests included advantages over traditional assays, general information on CS assays, and indications for testing (each 18%).

Conclusion

Future educational efforts may focus on limitations of OS assays, indications for CS assay diagnosis/monitoring, and support for clinic-laboratory dialog.

Evaluation of chromogenic factor IX assays by automated protocols

INTRODUCTION

Chromogenic substrate assays (CSA) to measure Factor IX (FIX) have recently become commercially available. However, information on their performance characteristics and use in diagnostic haemostasis laboratories remains limited.

AIM

To evaluate the Hyphen Biomed (Hyphen) and Rossix FIX CSAs on fully automated coagulation analysers and compare them to the FIX one-stage assay (OSA). This study was conducted in a tertiary referral haemostasis laboratory associated with a haemophilia treatment centre.

METHODS

Automated CSA protocols were adapted to the Sysmex CS2500 (CS2500) and Diagnostica Stago STA-R (STA-R) analysers. Samples assayed were from healthy volunteers, haemophilia B patients and FIX deficient plasma spiked with either plasma derived, recombinant or extended half-life FIX products.

RESULTS

Reference intervals for Hyphen and Rossix assays were 73 IU/dL to 164 IU/dL and 73 IU/dL to 168 IU/dL, respectively, on the CS2500 analyser; and 84 IU/dL to 165 IU/dL for the Rossix assay on the STA-R. Repeatability across all method/analyser combinations resulted in CVs ranging from 0.8% to 5.4%. Between run reproducibility gave CVs <6.7% for all method/analyser combinations. In spiked samples, FIX recoveries were mostly within an acceptable limit of 100 ± 25% for BeneFIX^® , Rixubis^® and Alprolix^® with some differences between CSAs.

CONCLUSION

Both commercial factor FIX CSA kits can be adapted for Stago and Sysmex automated coagulation analysers. Reagent cost and workflow practices will need to be considered. These assays are potentially more consistent than OSA in measurement of replacement FIX products in haemophilia B patients.

Qualification of a select one-stage activated partial thromboplastin time-based clotting assay and two chromogenic assays for the post-administration monitoring of nonacog beta pegol

Essentials Nonacog beta pegol (N9-GP) is an extended half-life, recombinant human factor IX (FIX). One-stage clotting (OSC) and chromogenic FIX activity assays were assessed for N9-GP recovery. OSC STA® -Cephascreen® , ROX FIX and BIOPHEN FIX chromogenic assays were qualified for N9-GP. Other extended half-life factor products should be assessed in a similar way prior to approval.

SUMMARY

Background Nonacog beta pegol (N9-GP) is an extended half-life, glycoPEGylated recombinant human factor IX that is under development for the prophylaxis and treatment of bleeding episodes in hemophilia B patients. Considerable reagent-dependent variability has been observed when one-stage clotting assays are used to measure the recovery of recombinant FIX products, including N9-GP. Objective To qualify select one-stage clotting and chromogenic FIX activity assays for measuring N9-GP recovery. Methods The accuracy and precision of the one-stage clotting assay (with the STA-Cephascreen activated partial thromboplastin [APTT] reagent) and the ROX Factor IX and BIOPHEN Factor IX chromogenic assays for measuring N9-GP recovery were assessed in N9-GP-spiked hemophilia B plasma samples in a systematic manner at three independent sites, with manufacturer-recommended protocols and/or site-specific assay setups, including different instruments. Results For each of the three FIX activity assays qualified on five different reagent-instrument systems, acceptable intra-assay and interassay accuracy and precision, dilution integrity, reagent robustness and freeze-thaw and short-term sample stabilities were demonstrated. The STA-Cephascreen assay showed a limited reportable range at one of the three qualification sites, and the BIOPHEN Factor IX assay showed suspect low-end sensitivity at one of the three qualification sites. An individual laboratory would account for these limitations by adjusting the assay's reportable range; thus, these findings are not considered to impact the respective assay qualifications. Conclusion The one-stage clotting assay with the STA-Cephascreen APTT reagent, the ROX Factor IX chromogenic assay and the BIOPHEN Factor IX chromogenic assay are considered to be qualified for the measurement of N9-GP in 3.2% (0.109 m) citrated human plasma.

The History of Clotting Factor Concentrates Pharmacokinetics

Clotting factor concentrates (CFCs) underwent tremendous modifications during the last forty years. Plasma-derived concentrates made the replacement therapy feasible not only in the hospital but also at patients’ home by on-demand or prophylactic regimen. Virucidal methods, implemented soon after hepatitis and AIDS outbreak, and purification by Mabs made the plasma-derived concentrates safer and purer. CFCs were considered equivalent to the other drugs and general rules and methods of pharmacokinetics (PK) were applied to their study. After the first attempts by graphical methods and calculation of In Vivo Recovery, compartment and non-compartment methods were applied also to the study of PK of CFCs. The bioequivalence of the new concentrates produced by means of recombinant DNA biotechnology was evaluated in head-to-head PK studies. Since the beginning, the large inter-patient variability of dose/response of replacement therapy was realized. PK allowed tailoring haemophilia therapy and PK driven prophylaxis resulted more cost effective. Unfortunately, the need of several blood samples and logistic difficulties made the PK studies very demanding. Recently, population PK (PopPK) has been applied to the prediction of CFCs dosing by Bayesian methodology. By PopPK also sparse data may allow evaluating the appropriateness of replacement therapy.

One-Stage Factor VIII Assays

Coagulation factor assays using one-stage methodology are widely used to measure factor levels for the purpose of detecting a deficiency, or to monitor replacement therapy. In this chapter, we focus on a method to measure Factor VIII coagulant activity (FVIII:C) by the one-stage assay (FVIII:C-1), with extra information provided to also allow this method to apply to Factor IX (FIX), Factor XI (FXI), and Factor XII (FXII). From the perspective of laboratory testing, these factors are components of the "intrinsic" coagulation pathway and are all measured in test systems based on the correction of the Activated Partial Thromboplastin Time (APTT). Factor activity is assessed by measuring the ability of an unknown sample to correct the prolonged APTT of factor-deficient plasma (deficient in the factor of interest), relative to the effect of a known calibrator. These assays are used for the diagnosis of the many causes of reduced factor levels, including those causing a prolonged APTT. It is important for laboratory staff to understand the impact of method variations, limitations, and result interpretation and these aspects are also discussed.

Factor VIII chromogenic assays can be used for potency labeling and postadministration monitoring of N8-GP

Essentials Chromogenic assays may be less variable than one-stage clot assays for measuring modified factor VIII. Chromogenic assays were evaluated for N8-GP potency labeling and postadministration monitoring. There was no significant difference between chromogenic assay kits for measuring N8-GP potency. Postadministration monitoring of N8-GP was comparable to turoctocog alfa for all kits tested.

SUMMARY

Background Factor VIII activity (

FVIII

C) is commonly measured using one-stage activated partial thromboplastin time (aPTT)-based clot assays. Chromogenic assays are, however, an alternative, and potency assessment in Europe is performed using chromogenic assays. One-stage clot assays are in general associated with high variability, and modified FVIII products may add to this variability. FVIII chromogenic assays may be less affected. Objectives To evaluate available chromogenic assay kits for potency labeling of polyethylene glycol-glycoconjugated turoctocog alfa (turoctocog alfa pegol [N8-GP]) and to evaluate selected chromogenic kits for postadministration monitoring of N8-GP using turoctocog alfa (Novoeight(®) ) as comparator. Methods Six FVIII chromogenic assay kits were adapted to the European Pharmacopeia guidelines for potency labeling, including assessment of time to 50% FX activation. Four kits were adapted for postadministration monitoring using an ACL(®) TOP 500 analyzer. Severe hemophilia A plasma was spiked with N8-GP or turoctocog alfa to simulate postadministration samples. The World Health Organization (WHO) 8th International Standard (IS) FVIII concentrate was used as calibrator throughout. In addition, a plasma calibrator was used for postadministration samples. Results When measuring N8-GP potency, no significant difference using a 1% significance level was observed between kits. In simulated postadministration samples, all test kits were highly accurate and precise, except at low concentrations, with no significant difference between

FVIII

C (P > 0.05) measured using the different calibrators. However, values obtained using the WHO 8th IS were closer to labeled values. Conclusions Chromogenic assay kits tested measured consistent

FVIII

C for N8-GP potency and showed comparable results for N8-GP and turoctocog alfa in simulated postadministration samples.

Measuring factor IX activity of nonacog beta pegol with commercially available one-stage clotting and chromogenic assay kits: a two-center study

Essentials Validated assays are required to precisely measure factor IX (FIX) activity in FIX products. N9-GP and two other FIX products were assessed in various coagulation assay systems at two sites. Large variations in FIX activity measurements were observed for N9-GP using some assays. One-stage and chromogenic assays accurately measuring FIX activity for N9-GP were identified.

SUMMARY

Background Measurement of factor IX activity (FIX:C) with activated partial thromboplastin time-based one-stage clotting assays is associated with a large degree of interlaboratory variation in samples containing glycoPEGylated recombinant FIX (rFIX), i.e. nonacog beta pegol (N9-GP). Validation and qualification of specific assays and conditions are necessary for the accurate assessment of FIX:C in samples containing N9-GP. Objectives To assess the accuracy of various one-stage clotting and chromogenic assays for measuring FIX:C in samples containing N9-GP as compared with samples containing rFIX or plasma-derived FIX (pdFIX) across two laboratory sites. Methods FIX:C, in severe hemophilia B plasma spiked with a range of concentrations (from very low, i.e. 0.03 IU mL(-1) , to high, i.e. 0.90 IU mL(-1) ) of N9-GP, rFIX (BeneFIX), and pdFIX (Mononine), was determined at two laboratory sites with 10 commercially available one-stage clotting assays and two chromogenic FIX:C assays. Assays were performed with a plasma calibrator and different analyzers. Results A high degree of variation in FIX:C measurement was observed for one-stage clotting assays for N9-GP as compared with rFIX or pdFIX. Acceptable N9-GP recovery was observed in the low-concentration to high-concentration samples tested with one-stage clotting assays using SynthAFax or DG Synth, or with chromogenic FIX:C assays. Similar patterns of FIX:C measurement were observed at both laboratory sites, with minor differences probably being attributable to the use of different analyzers. Conclusions These results suggest that, of the reagents tested, FIX:C in N9-GP-containing plasma samples can be most accurately measured with one-stage clotting assays using SynthAFax or DG Synth, or with chromogenic FIX:C assays.