International comparative field study evaluating the assay performance of AFSTYLA in plasma samples at clinical hemostasis laboratories

A Generative and Causal Pharmacokinetic Model for Factor VIII in Hemophilia A: A Machine Learning Framework for Continuous Model Refinement

In rare diseases, such as hemophilia A, the development of accurate population pharmacokinetic (PK) models is often hindered by the limited availability of data. Most PK models are specific to a single recombinant factor VIII (rFVIII) concentrate or measurement assay, and are generally unsuited for answering counterfactual ("what-if") queries. Ideally, data from multiple hemophilia treatment centers are combined but this is generally difficult as patient data are kept private. In this work, we utilize causal inference techniques to produce a hybrid machine learning (ML) PK model that corrects for differences between rFVIII concentrates and measurement assays. Next, we augment this model with a generative model that can simulate realistic virtual patients as well as impute missing data. This model can be shared instead of actual patient data, resolving privacy issues. The hybrid ML-PK model was trained on chromogenic assay data of lonoctocog alfa and predictive performance was then evaluated on an external data set of patients who received octocog alfa with FVIII levels measured using the one-stage assay. The model presented higher accuracy compared with three previous PK models developed on data similar to the external data set (root mean squared error = 14.6 IU/dL vs. mean of 17.7 IU/dL). Finally, we show that the generative model can be used to accurately impute missing data (< 18% error). In conclusion, the proposed approach introduces interesting new possibilities for model development. In the context of rare disease, the introduction of generative models facilitates sharing of synthetic data, enabling the iterative improvement of population PK models.

Variability in combinations of APTT reagent and substrate plasma for a one-stage clotting assay to measure factor VIII products

INTRODUCTION

An investigation of the suitability of reagents for measuring FVIII products in a one-stage clotting assay (OSA) showed variations in their FVIII activity (FVIII:C). Most studies have focused on the activated partial thromboplastin time (APTT) reagent rather than FVIII-deficient plasma (F8DP), even though the APTT-based OSA is comprised of APTT reagents and factor-deficient plasma.

AIM

A single-centre study was conducted to clarify variations in measurements of FVIII products in an OSA using a total of 12 reagent combinations, including four APTT reagents and three types of F8DP.

METHODS

FVIII:C in nine types of FVIII product-spiked plasma was measured using an OSA with four different APTT reagents and three types of F8DP.

RESULTS

F8DP-dependent variations were found in addition to differences derived from APTT reagents. Variations in target recovery (TR) were observed for NovoEight®, Eloctate®, and Jivi®. Reduced TR for Jivi was found only for Pathromtin SL in combination with congenital F8DP (F8DP-3). This lower TR was not observed with alternative manufacturing lots of F8DP-3. The reduced TR for Jivi might be related to impaired contact activation due to lower factor XI activity in F8DP-3.

CONCLUSION

In addition to APTT reagents, variations in F8DPs used for OSAs can also affect FVIII:C results. F8DPs as well as the APTT reagent used for OSA should be chosen with caution, and laboratories should evaluate reagents for F8DPs as they currently do for APTT reagents, especially when lot changes occur.

A global comparative field study to evaluate the factor VIII activity of efanesoctocog alfa by one-stage clotting and chromogenic substrate assays at clinical haemostasis laboratories

INTRODUCTION

Structural and chemical modifications of factor VIII (FVIII) products may influence their behaviour in FVIII activity assays. Hence, it is important to assess the performance of FVIII products in these assays. Efanesoctocog alfa is a new class of FVIII replacement therapy designed to provide both high sustained factor activity levels and prolonged plasma half-life.

AIM

Evaluate the accuracy of measuring efanesoctocog alfa FVIII activity in one-stage clotting assays (OSAs) and chromogenic substrate assays (CSAs).

METHODS

Human plasma with no detectable FVIII activity was spiked with efanesoctocog alfa or a full-length recombinant FVIII product comparator, octocog alfa, at nominal concentrations of 0.80 IU/mL, 0.20 IU/mL, or 0.05 IU/mL, based on labelled potency. Clinical haemostasis laboratories (N = 35) tested blinded samples using in-house assays. Data from 51 OSAs (14 activated partial thromboplastin time [aPTT] reagents) and 42 CSAs (eight kits) were analyzed.

RESULTS

Efanesoctocog alfa activity was reliably (±25% of nominal activity) measured across all concentrations using OSAs with Actin FSL and multiple other aPTT reagents. Under- and overestimation of FVIII activity occurred with some reagents. No specific trend was observed for any class of aPTT activators. A two- to three-fold overestimation was consistently observed using CSAs and the OSA with Actin FS as the aPTT reagent across evaluated concentrations.

CONCLUSION

Under- or overestimation occurred with some specific OSAs and most CSAs, which has been previously observed with other modified FVIII replacement products. Efanesoctocog alfa FVIII activity was measured with acceptable accuracy and reliability using several OSA methods and commercial plasma standards.

Factor VIII and Factor IX Activity Measurements for Hemophilia Diagnosis and Related Treatments

Accurate measurement of clotting factors VIII (FVIII) or IX (FIX) is vital for comprehensive diagnosis and management of patients with hemophilia A or B. The one-stage activated partial thromboplastin time (aPTT)-based clotting assay is the most commonly used method worldwide for testing FVIII or FIX activities. Alternatively, FVIII and FIX chromogenic substrate assays, which assess the activation of factor X, are available in some specialized laboratories. The choice of reagent or methodology can strongly influence the resulting activity. Variation between one-stage FVIII or FIX activities has been reported in the measurement of some standard and extended half-life factor replacement therapies and gene therapy for hemophilia B using different aPTT reagents. Discrepancy between one-stage and chromogenic reagents has been demonstrated in some patients with mild hemophilia A or B, the measurement of some standard and extended half-life factor replacement therapies, and the transgene expression of hemophilia A and B patients who have received gene therapy. Finally, the measurement of bispecific antibody therapy in patients with hemophilia A has highlighted differences between chromogenic assays. It is imperative that hemostasis laboratories evaluate how suitable their routine assays are for the accurate measurement of the various hemophilia treatment therapies.

Plasma Clearance of Coagulation Factor VIII and Extension of Its Half-Life for the Therapy of Hemophilia A: A Critical Review of the Current State of Research and Practice

Factor VIII (FVIII) is an important component of blood coagulation as its congenital deficiency results in life-threatening bleeding. Current prophylactic therapy of the disease (hemophilia A) is based on 3-4 intravenous infusions of therapeutic FVIII per week. This poses a burden on patients, demanding reduction of infusion frequency by using FVIII with extended plasma half-life (EHL). Development of these products requires understanding FVIII plasma clearance mechanisms. This paper overviews (i) an up-to-date state of the research in this field and (ii) current EHL FVIII products, including recently approved efanesoctocog alfa, for which the plasma half-life exceeds a biochemical barrier posed by von Willebrand factor, complexed with FVIII in plasma, which results in ~1 per week infusion frequency. We focus on the EHL FVIII products' structure and function, in particular related to the known discrepancy in results of one-stage clotting (OC) and chromogenic substrate (CS) assays used to assign the products' potency, dosing, and for clinical monitoring in plasma. We suggest a possible root cause of these assays' discrepancy that is also pertinent to EHL factor IX variants used to treat hemophilia B. Finally, we discuss approaches in designing future EHL FVIII variants, including those to be used for hemophilia A gene therapy.

Relationship between factor VIII levels and bleeding for rFVIII-SingleChain in severe hemophilia A: A repeated time-to-event analysis

Publications on the exposure-effect relationships of factor concentrates for hemophilia treatment are limited, whereas such analyses give insight on treatment efficacy. Our objective was to examine the relationship between the dose, factor VIII (FVIII) levels and bleeding for rFVIII-SingleChain (lonoctocog alfa, Afstyla). Data from persons with severe hemophilia A on rFVIII-SingleChain prophylaxis from three clinical trials were combined. The published rFVIII-SingleChain population pharmacokinetic (PK) model was evaluated and expanded. The probability of bleeding was described with a parametric repeated time-to-event (RTTE) model. Data included 2080 bleeds, 2545 chromogenic stage assay, and 3052 one-stage assay FVIII levels from 241 persons (median age 19 years) followed for median 1090 days. The majority of the bleeds occurred in joints (65%) and the main bleeding reason was trauma (44%). The probability of bleeding decreased during follow-up and a FVIII level of 8.9 IU/dL (95% confidence interval: 6.9-10.9) decreased the bleeding hazard by 50% compared to a situation without FVIII in plasma. Variability in bleeding hazard between persons with similar FVIII levels was large, and the pre-study annual bleeding rate explained part of this variability. When a FVIII trough level of 1 or 3 IU/dL is targeted during prophylaxis, simulations predicted two (90% prediction interval [PI]: 0-17) or one (90% PI: 0-11) bleeds per year, respectively. In conclusion, the developed PK-RTTE model adequately described the relationship between dose, FVIII levels and bleeds for rFVIII-SingleChain. The obtained estimates were in agreement with those published for the FVIII concentrates BAY 81-8973 (octocog alfa) and BAY 94-9027 (damoctocog alfa pegol), indicating similar efficacy to reduce bleeding.

Emicizumab assay evaluations and results from an Australian field study of emicizumab measurement

Emicizumab is a recombinant, humanised bispecific antibody which acts as a FVIII mimetic and is a therapeutic option for haemophilia A. Plasma emicizumab levels may sometimes be required. Multiple one-stage clotting assays (OSA) and one human component chromogenic assay (CSA) were used to measure emicizumab both centrally and by a field study. The study samples drug concentrations range included within therapy range of 35-70 μg/mL. All assays were modified from traditional FVIII assays to enable replacement of plasma calibrators with emicizumab calibrators. Central laboratory OSA mean recovery levels (target) for six spike levels of emicizumab were close to target at 120.5 (120), 81.6 (80), 40.9 (40), 21.4 (20), 10.7 (10) and 5.5 (5) μg/mL. Field study OSA mean recoveries were similarly close to target. Between method coefficients of variation were <9% in both the central laboratory and field study assays, except for the 5 μg/mL sample which was 12.3%. CSA mean recoveries were within 10% of target at 80, 50 and 20 μg/mL levels. This study affirms that emicizumab can be measured by OSA using many types of activated partial thromboplastin time (APTT) reagents and is also measurable by the human CSA. The assays showed good precision, accuracy and linearity both locally and in a field study setting.

An Update on Laboratory Diagnostics in Haemophilia A and B

Haemophilia A (HA) and B (HB) are X-linked hereditary bleeding disorders caused by lack of activity of coagulation factors VIII (FVIII) or IX (FIX), respectively. Besides conventional products, modern replacement therapies include FVIII or FIX concentrates with an extended half-life (EHL-FVIII/FIX). Two main strategies for measuring plasma FVIII or FIX activity are applied: the one-stage clotting assay (OSCA) and the chromogenic substrate assay (CSA), both calibrated against plasma (FVIII/FIX) standards. Due to the structural modifications of EHL-FVIII/FIX, reagent-dependent assay discrepancies have been described when measuring the activity of these molecules. Assay discrepancies have also been observed in FVIII/FIX gene therapy approaches. On the other hand, nonfactor replacement by the bispecific antibody emicizumab, a FVIIIa-mimicking molecule, artificially shortens activated partial thromboplastin time–based clotting times, making standard OSCAs inapplicable for analysis of samples from patients treated with this drug. In this review, we aim to give an overview on both, the currently applied and future therapies in HA and HB with or without inhibitors and corresponding test systems suitable for accompanying diagnostics.

Monitoring of different factor VIII replacement products using a factor VIII one-stage clotting assay on cobas t 511/711 analysers

INTRODUCTION

Recombinant coagulation factor VIII (FVIII) products are the standard of care for patients with haemophilia A. The development of modified FVIII products has provided benefit for patients but presented challenges for monitoring FVIII activity.

AIM

This single-centre study evaluated the Roche FVIII one-stage clotting assay (OSA) in measuring FVIII activity in plasma samples spiked with seven FVIII products at clinically relevant concentrations.

METHODS

FVIII-deficient plasma samples were spiked with two batches of recombinant FVIII products (octocog alfa, moroctocog alfa, simoctocog alfa, efmoroctocog alfa, damoctocog alfa pegol, rurioctocog alfa pegol, lonoctocog alfa) at 1-120 IU/dL FVIII activity, according to their labelled potency. Measurement was conducted on the cobas t 511/711 analysers using the Roche FVIII OSA and the Technoclone TECHNOCHROM FVIII:C chromogenic substrate assay (CSA).

RESULTS

Using the OSA, FVIII activity was close to labelled potency for most analysed FVIII products including a recombinant FVIII Fc fusion protein. PEGylated FVIII product, damoctocog alfa pegol, was marginally above and single-chain product, lonoctocog alfa, below the predefined acceptance criteria: for FVIII activity < 25 IU/dL: ± 5 IU/dL; for FVIII activity ≥ 25 IU/dL: ± 20% (relative). The different principles of OSA and CSA led to discrepancies in the estimation of all analysed FVIII products. Additionally, in vitro recovery was increased at lower levels of FVIII activity using the OSA, whereas recovery was more consistent using the CSA.

CONCLUSION

These data allow the interpretation of FVIII activity results for different FVIII products using the Roche FVIII OSA on the cobas t 511/711 analysers.

Considerations on activity assay discrepancies in factor VIII and factor IX products

New modified coagulation factor VIII (FVIII) and factor IX (FIX) products have been designed to improve the treatment of individuals with hemophilia A and B by increasing the interval between dosing. Although these FVIII and FIX molecules have been structurally modified to improve the circulation time, the changes have also influenced their behavior in functional assays in comparison with traditional plasma-derived or recombinant coagulation factors. The assignment of potencies for these products can be problematic because discordance in factor activity values between the commonly used one-stage clotting and chromogenic substrate assays is often observed. Discrepancies in potency assay values also exist when different assay kits and reagents are used in the same assay type. Ideally, all FVIII and FIX products should be calibrated against the World Health Organization (WHO) International Standards (IS) because the assignment of potencies in international units (IU) helps maintain treatment tradition and meaningful references for manufacturers, patients, and clinicians. The discrepant measurements, attributed to the modified structural and functional properties of these products, are manifested in their lack of commutability with the WHO IS for FVIII or FIX. Herein, we discuss the considerations upon which an assay is chosen for potency assignment and postadministration monitoring of a new factor product, which include the validity of the assay calibrated with the IS, the meaning of the potency values in IU, standards of care for patients, clinical relevance between the assigned potency value and recovery value from clinical laboratories, and patient safety.

Activity of transgene-produced B-domain-deleted factor VIII in human plasma following AAV5 gene therapy

Adeno-associated virus (AAV)-based gene therapies can restore endogenous factor VIII (FVIII) expression in hemophilia A (HA). AAV vectors typically use a B-domain-deleted FVIII transgene, such as human FVIII-SQ in valoctocogene roxaparvovec (AAV5-FVIII-SQ). Surprisingly, the activity of transgene-produced FVIII-SQ was between 1.3 and 2.0 times higher in one-stage clot (OS) assays than in chromogenic-substrate (CS) assays, whereas recombinant FVIII-SQ products had lower OS than CS activity. Transgene-produced and recombinant FVIII-SQ showed comparable specific activity (international units per milligram) in the CS assay, demonstrating that the diverging activities arise in the OS assay. Higher OS activity for transgene-produced FVIII-SQ was observed across various assay kits and clinical laboratories, suggesting that intrinsic molecular features are potential root causes. Further experiments in 2 participants showed that transgene-produced FVIII-SQ accelerated early factor Xa and thrombin formation, which may explain the higher OS activity based on a kinetic bias between OS and CS assay readout times. Despite the faster onset of coagulation, global thrombin levels were unaffected. A correlation with joint bleeds suggested that both OS and CS assay remained clinically meaningful to distinguish hemophilic from nonhemophilic FVIII activity levels. During clinical development, the CS activity was chosen as a surrogate end point to conservatively assess hemostatic efficacy and enable comparison with recombinant FVIII-SQ products. Relevant trials are registered on clinicaltrials.gov as #NCT02576795 and #NCT03370913 and, respectively, on EudraCT (European Union Drug Regulating Authorities Clinical Trials Database; https://eudract.ema.europa.eu) as #2014-003880-38 and #2017-003215-19.

Extended Half-Life Factor VIII/Factor IX Products: Assay Discrepancies and Implications for Hemophilia Management

Due to structural differences between extended half-life (EHL) factor VIII (FVIII) or FIX products and equivalent plasma wild-type molecules used for assay calibration, reagent-dependent discrepancies during monitoring of FVIII- and FIX-replacement therapies with EHL products have been described. To assess the performance of available one-stage clotting and chromogenic substrate assays on the Siemens Atellica COAG 360 analyzer, an in vitro study using spiked plasma samples was performed. The described results confirm previously described findings and allowed allocation of each EHL product to an appropriate assay. In addition, corresponding EHL product-specific analytes were defined within the order entry system of the University Hospital Bonn. The requirement of product-specific FVIII and FIX assays complicates patient monitoring and demonstrates the need for both continuous education and communication between treating physicians and the coagulation laboratory.

Laboratory testing in hemophilia: Impact of factor and non-factor replacement therapy on coagulation assays

The advent of extended half-life (EHL) recombinant clotting factors and innovative non-factor replacement therapeutics, such as emicizumab, offers several advantages over existing products for the prophylactic treatment of people living with hemophilia (PwH). These include low annual bleeding rates with less frequent dosing, higher trough plasma concentrations, and a more convenient route of administration. However, increasing use of these therapies poses challenges to clinicians and coagulation laboratories due to the lack of standardized assays for monitoring of hemostatic parameters, and the potential for misinterpretation of test results, which may jeopardize patient safety. Definitive diagnosis of hemophilia and treatment monitoring is reliant on demonstrating factor VIII (FVIII; hemophilia A) or factor IX (FIX; hemophilia B) deficiency using a functional coagulation assay. The most frequently used assays are based on activated partial thromboplastin time, using a one-stage or two-stage process. While one-stage and chromogenic assays have performed well with human-derived FVIII and FIX and full-length recombinant products, EHL recombinant factors are heterogeneous in structure and mode of action and therefore show wide variation in activity levels between different one-stage assays, and between one-stage and chromogenic assays. In the context of the recommended stepwise approach for laboratory diagnosis of hemophilia, we examine the diagnostic challenges associated with the use of EHL factors and novel non-factor therapeutics and consider the optimal diagnostic approach in PwH who are receiving these treatments. Ultimately, accurate diagnostic solutions are a prerequisite for personalized therapy to minimize treatment burden and improve quality of life in PwH.

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.

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.

Estimation of Nuwiq® (simoctocog alfa) activity using one-stage and chromogenic assays-Results from an international comparative field study

Background

Accurate determination of coagulation factor VIII activity (FVIII:C) is essential for effective and safe FVIII replacement therapy. FVIII:C can be measured by one‐stage and chromogenic substrate assays (OSAs and CSAs, respectively); however, there is significant interlaboratory and interassay variability.

Aims

This international comparative field study characterized the behaviour of OSAs and CSAs used in routine laboratory practice to measure the activity of Nuwiq^® (human‐cl rhFVIII, simoctocog alfa), a fourth‐generation recombinant human FVIII produced in a human cell line.

Methods

FVIII‐deficient plasma was spiked with Nuwiq^® or Advate^® at 1, 5, 30 and 100 international units (IU)/dL. Participating laboratories analysed the samples using their routine procedures and equipment. Accuracy, inter‐ and intralaboratory variation, CSA:OSA ratio and the impact of different OSA and CSA reagents were assessed.

Results

Forty‐nine laboratories from 9 countries provided results. Mean absolute FVIII:C was comparable for both products at all concentrations with both OSA and CSA, with interproduct ratios (Nuwiq^®:Advate^®) of 1.02‐1.13. Mean recoveries ranged from 97% to 191% for Nuwiq^®, and from 93% to 172% for Advate^®, with higher recoveries at lower concentrations. Subgroup analyses by OSA and CSA reagents showed minor variations depending on reagents, but no marked differences between the two products. CSA:OSA ratios based on overall means ranged from 0.99 to 1.17 for Nuwiq^® and from 1.01 to 1.17 for Advate^®.

Conclusions

Both OSAs and CSAs are suitable for the measurement of FVIII:C of Nuwiq^® in routine laboratory practice, without the need for a product‐specific reference standard.

Evaluation of an automated chromogenic assay for Factor VIII clotting activity measurement in patients affected by haemophilia A

INTRODUCTION

The original one-stage clotting assay is still the most widely used method to measure Factor VIII clotting activity (FVIII:C) in patients with haemophilia A (HA), although the use of chromogenic assays is increasing significantly.

AIM

Evaluation of the analytical performance and diagnostic accuracy of BIOPHEN™ FVIII:C (HYPHEN BioMed, Neuville-sur-Oise, France) assay on Sysmex CS-2400 (Sysmex, Kobe, Japan) analyser.

METHODS

Sixty patients with haemophilia A (HA; any severity) and 120 healthy Italian subjects were included. All the assays were performed on citrate platelet-poor plasmas stored at -80°C. Chromogenic BIOPHEN™ FVIII:C was compared with the one-stage assay using Actin FS and Factor VIII deficient plasma (Siemens Healthcare Diagnostics, Marburg, Germany) on Sysmex CS-2400 and with another chromogenic automated assay (COAMATIC™ Factor VIII, CHROMOGENIX on ACL TOP analyzer; Instrumentation Laboratory, Milan, Italy).

RESULTS

Intra-assay and inter-assay coefficient of variation were <6%. Linearity was good up to 1/128 dilution (r = 0.99); mean recovery was 91.7% and limit of detection was 0.2%. BIOPHEN™ FVIII:C assay showed a good correlation and diagnostic agreement with the chromogenic COAMATIC™ assay: the Spearmen's Rank correlation coefficient was 0.98 and the inter-rate agreement K Cohen coefficient was 0.61. The K coefficient was 0.91 when BIOPHEN™ FVIII:C was compared with the historical classification of the patients, demonstrating an optimal diagnostic accuracy in HA.

CONCLUSIONS

BIOPHEN™ FVIII:C showed good analytical performance and diagnostic accuracy and could be considered suitable for the introduction in routine analytical panel of coagulation for the diagnosis of HA patients.

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.

Hemophilia trials in the twenty-first century: Defining patient important outcomes

Treatment for hemophilia has advanced dramatically over the past 5 decades. Success of prophylactic therapy in preventing bleeding and decreasing associated complications has established a new standard of care. However, with the advent of gene therapy and treatments that effectively mimic sustained coagulation factor replacement, outcome measures that worked well for assessing factor replacement therapies in past clinical trials need to be reassessed. In addition, while therapies have advanced, so has the science of outcome assessment, including recognition of the importance of patient important and patient reported outcomes. This manuscript reviews strengths and limitations of outcome measures used in hemophilia from both a provider and patient perspective.

Bioengineered molecules for the management of haemophilia: Promise and remaining challenges

Recombinant DNA technology has led to accelerating introduction of novel therapeutics for the treatment of haemophilia. This technology has driven the development of recombinant clotting factors, extended half-life clotting factors, alternative biologics to promote haemostasis and enabled the launch of the gene therapy era for haemophilia. At the core of this technology is the ability to study the structure and function of the native molecules and to apply rational bioengineering to overcome limitations to the existing therapies. Through the study of haemophilia-causing mutations, site-directed mutagenesis, detailed structural models and a wide repertoire of animal models, new bioengineering strategies are helping overcome some of the remaining limitations and challenges of traditional clotting factor concentrates. Some of these bioengineering strategies are now being partnered with improvements in vectorology leading to the first wave of successful gene therapy approaches. This study will review past and present bioengineered molecules that are advancing care for haemophilia as well as novel approaches that promise to continue to improve care and outcomes for patients with haemophilia.

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.

Shifting Landscape of Hemophilia Therapy: Implications for Current Clinical Laboratory Coagulation Assays

Clinical coagulation assays are an integral part of diagnosing and managing patients with hemophilia; however, in this new era of bioengineered factor products and non-factor therapeutics, problems have arisen with use of traditional coagulation tests for the quantification of several of these new products. Discussion over the use of one-stage clotting assays versus chromogenic substrate assays for clinical decision making and potency labeling has been ongoing for many years. Emerging factor concentrates have heightened concern over assay selection and availability. Emicizumab interferes with all aPTT based assays, rendering them unreliable and potentially falsely reassuring to the unaware provider. This review explores considerations for coagulation assays in the clinical setting and highlights how awareness of institutional coagulation assays and potential limitations have never been more critical for providers caring for patients with bleeding disorders. This article is protected by copyright. All rights reserved.