Measuring FVIII activity of glycopegylated recombinant factor VIII, N8-GP, with commercially available one-stage clotting and chromogenic assay kits: a two-centre study

The Role of Clot Waveform Analysis and Related Parameters in the Diagnosis and Treatment of Hemophilia A

BACKGROUND

 Hemophilia A (HA) is an inherited bleeding disorder caused by a deficiency or defect in factor VIII (FVIII).

METHODS

 We investigated the role of clot waveform analysis (CWA) of activated partial thromboplastin time in the diagnosis and therapeutic monitoring of HA. The changes in CWA parameters the maximum clotting velocity (|Min1|), maximum clotting acceleration (|Min2|), and maximum clotting deceleration (|Max2|) were detected among mild, moderate, and severe HA groups.

RESULTS

 As the severity of HA subtypes increased, the levels of |Min1|, |Min2|, and |Max2| progressively decreased (p < 0.05). Receiver operating characteristic curve analysis showed that |Max2| and |Min2| were more effective than |Min1| in distinguishing different types of HA patients, with higher diagnostic efficacy. The standard curves based on Actin FSL reagent for normal and low levels of FVIII:C-|Max2| were established, with R2 values of 0.98 and 0.99, respectively. These curves can be utilized for monitoring during replacement therapies involving full-length recombinant FVIII and B-domain-deleted FVIII. Thirty cases of HA patients utilized the FVIII-|Max2| standard curve to obtain individual pharmacokinetics characteristic parameters. The clearance, half-life (t1/2), time to FVIII:C of 1% above baseline (tt1%), and predicted dosage showed no statistically significant differences compared with one-stage assay (p > 0.05).

CONCLUSION

 CWA is an economical and practical tool, and its related parameters are associated with the severity of HA. It has promising clinical prospects in predicting FVIII:C levels and individualized treatment when HA patients undergo replacement therapy.

Pharmacokinetics of Efmoroctocog alfa by Two-Compartment Model Highlights Hemophilia A Patients with Biphasic Decay, Long Mean Residence Time, and Beta Half-Life

Background/Objectives: A compartmental pharmacokinetics (PK) analysis of new extended half-life FVIII concentrates has never been performed in a large cohort of hemophilia patients. An improved PK analysis of individual outcomes may help to tailor hemophilia replacement treatment. Methods: PK outcomes after the infusion of a standard single dose of Efmoroctocog alfa were collected from 173 patients with severe/moderately severe hemophilia A in 11 Italian hemophilia centers. Factor VIII clotting activity (FVIII:C) was measured by one-stage clotting assay (OSA) in all patients, and chromogenic substrate assay (CSA) in a subgroup (n = 52). Fifty patients underwent a comparative PK assessment with standard half-life (SHL) recombinant FVIII (rFVIII) products. Non-compartmental analysis (NCA), one compartment model (OCM), and TCM were used to analyze the decay curves of all patients, and one-way paired ANOVA to compare the PK outcomes. Results: All 173 PKs conformed to the NCA and OCM, but only 106 (61%) conformed to the TCM based on the biphasic features of their decay curves. According to the TCM, the Beta HL and MRT of rFVIIIFc were 20.42 ± 7.73 and 25.64 ± 7.61 h, respectively. ANOVA analysis of the outcomes from the three PK models showed significant differences in clearance, half-life (HL), and mean residence time (MRT) (p < 0.001 for all parameters). As anticipated, the HL and MRT of rFVIIIFc were longer than those of SHL rFVIII. Comparing OSA with CSA outcomes, Cmax resulted higher when measured by CSA (p = 0.05) and, according to TCM, Beta HL resulted longer when measured by OSA (p = 0.03). FVIII:C trough levels obtained with SHL concentrates were significantly lower than those obtained with rFVIIIFc at each post-infusion time point. Conclusions: In a large group of hemophilia A (HA) patients, three different PK models confirmed the improved pharmacokinetic (PK) characteristics of rFVIIIFc, compared with standard half-life rFVIII concentrates. The TCM only fits two-thirds of the PKs, highlighting their biphasic decay and a long Beta half-life. In these patients, the TCM would be preferable to properly evaluate individual PK features.

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.

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.

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.

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.

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.

Laboratory issues in gene therapy and emicizumab

The treatment options for the haemostatic disorders, haemophilia A and haemophilia B, have progressed rapidly over the last decade. The introduction of extended half-life recombinant factor VIII (FVIII) and factor IX (FIX) concentrates to replace these missing clotting factors highlighted discordance between one-stage activated partial thromboplastin time (APTT)-based clotting factor assays and chromogenic factor assays with some products. This raised awareness of the importance of investigation of potential reagent or assay differences by pharmaceutical companies. In 2017, the FVIII mimetic, emicizumab, was approved as a prophylactic treatment for haemophilia A patients with anti-FVIII inhibitors. The mechanism of action of emicizumab causes interference with some commonly used haemostasis tests including the APTT and its associated one-stage APTT-based clotting assays. Chromogenic assays may also be affected but this is dependent on the particular constituents of the reagents. Chromogenic assays containing human factor IXa (FIXa) and factor X (FX) are sensitive to the presence of emicizumab but those containing bovine FIXa and FX are unaffected. Many haemostasis laboratories have been required to evaluate new assays to enable accurate monitoring of emicizumab in patient plasma. A number of gene therapy approaches have been trialled in both haemophilia A and haemophilia B but there are scant data published on the measurement of FVIII and FIX in these patients and whether there are discrepancies between reagents or assay methodologies.

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.

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 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.

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.

Effects of a novel low volume resuscitation solutions on coagulation and platelet function

Background

Novel crystalloid solutions containing polyethylene glycol polymers (PEG-20k) produce dramatic resuscitation effects but dose-dependently produce a hypocoagulative state. The objective of this study was to examine possible mechanisms of this effect. Based on previous thromboelastography data, we hypothesize the effect is largely due to platelet interactions with the polymers.

Methods

Whole citrated blood from healthy volunteers was diluted ex-vivo 10% with crystalloids and tested for coagulation and platelet function. The specific tests included prothrombin time (PT), activated partial thromboplastin time (aPTT), fibrinogen and von Willebrand factor (vWf) activity, thrombin generation, thromboelastography with and without platelet mapping, platelet flow cytometry, and erythrocyte sedimentation rate.

Findings

Fibrinogen and vWF activities, PT, and aPTT were not affected by PEG-20k dilutions. Thrombin activity was mildly suppressed with PEG-20k (TTP- 20%). Platelet mapping demonstrated significantly greater % inhibition of both ADP and arachidonic acid-induced platelet aggregation with PEG-20k, but direct ADP-activated gpIIa/IIIb (PAC1) and P-selectin (CD62P) binding site expression was not altered. Mild dose-dependent suppression of TEG-MA was seen with PEG-20k using platelet poor plasma. Erythrocyte Sedimentation Rates (ESR) were dramatically accelerated after dilution with 10% PEG-20k, which was competitively blocked by smaller PEG polymers, suggesting nonspecific PEG-20k cell binding effects.

Conclusions

PEG-20k creates a mild hypocoagulative state in whole blood at concentrations ≥10%, which may be due to platelet-PEG interactions at the IIb/IIIa interface with lesser effects on fibrin polymerization. This interaction may cause a functional thrombasthenia induced by nonspecific platelet surface passivation by the PEG polymer.

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.

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.

Advances in the Treatment of Hemophilia: Implications for Laboratory Testing

BACKGROUND

Until recently, clinical laboratories have monitored hemophilia treatment by measuring coagulation factors before/after infusion of human-derived or recombinant factors. Substantial changes are expected in the near future based on new therapeutic approaches that have been or are being developed.

CONTENT

Hemophilia treatment includes replacement therapy with human-derived/recombinant factors or treatment with bypassing agents for patients without or with inhibitors, respectively. Accordingly, laboratory methods for monitoring include one-stage clotting or chromogenic assays meant to measure either factor VIII/IX or global coagulation tests to measure the effect of bypassing agents. Recently, modified long-acting coagulation factors have been introduced for which discrepant results may be expected when measurement is performed with one-stage clotting or chromogenic assays. Currently, novel drugs not based on coagulation factors are under development and are being tested in clinical studies. These drugs do require new methods and therefore laboratory evaluation of hemophilia will undergo dramatic changes in the near future.

SUMMARY

From the analysis of the current practice and literature, we draw the following conclusions: (a) Thrombin generation or thromboelastometry are the logical candidate assays to monitor bypassing agents. (b) Considerable differences are expected when measuring modified long-acting coagulation factors, depending on whether one-stage or chromogenic assays are used. Although no definitive conclusions can presently be drawn, chromogenic assays are probably more suitable than one-stage clotting. (c) Novel drugs not based on coagulation factors such as emicizumab, fitusiran, or concizumab that are entering the market do require alternative methods that are not yet well established.

New challenges and best practices for the laboratory monitoring of factor VIII and factor IX replacement

Several recombinant factor VIII and factor IX concentrates with extended half-life (EHL) have recently been validated by clinical studies. The availability of these novel concentrates is expected to significantly facilitate the treatment of patients with hemophilia A and B. However, the modification applied to these molecules has introduced variations in their activity measurement in routine coagulation assays. Depending on the assays, underestimations of up to 10-fold or overestimations of up to approximately 30-fold in the measurements of the recovery have been reported in some factor concentrates. Such biases in monitoring may lead to major under- or overtreatment, as well as unnecessary searching for inhibitor antibodies. In this review, we discuss the guidelines and recommendations that allow the selection of optimal strategies to monitor patients treated with these novel factor concentrates. Based on the specificities of the assays and on local regulations, different chromogenic substrate assays in addition to one-stage clotting assays may be validated to allow the accurate measurement of all novel products. An efficient communication between the clinical laboratory and the clinicians is essential to ensure that the appropriate assays are carried out in laboratories and that the clinicians correctly evaluate the data. Further laboratory and clinical studies are still required for the optimization of the laboratory assays that can be used in the measurement of novel factor VIII and factor IX concentrates with EHL.

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.