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.

A next generation FVIII mimetic bispecific antibody, Mim8, the impact on non-factor VIII related haemostasis assays.

INTRODUCTION AND AIMS: Mim8 is a next generation bispecific antibody developed for the treatment of haemophilia A (HA). Mim8 has an increased potency compared to first generation molecules. The impact on Mim8 on non-FVIII measuring haemostasis assays was assessed in plasma containing Mim8. METHODS: Congenital severe HA plasma was spiked with increasing concentrations of Mim8 (0-20 µg/mL). 28 routine and specialist haemostasis assays were used to measure activities. These included tests for prothrombin time (PT), fibrinogen, thrombin, D-dimer, anti-Xa, heparin induced thrombocytopenia (HIT), clotting factors II-XII, factor XIII, von Willebrand factor (VWF), thrombophilia and DRVVT. RESULTS AND CONCLUSIONS: Less than 10 % difference was calculated between plasma without Mim8 and plasma spiked to 15 µg/mL Mim8 in all assays except thrombin time (-10.5%), APTT-based factor IX, XI and XII, Werfen VWF:RCo (10.6%) and Siemens LA1 (-26.4%) and LA2 (-16.9%). At the expected therapeutic steady state levels of Mim8 (5-8 µg/mL), less than 10% difference was calculated for thrombin time and Werfen VWF:RCo. APTT-based assays of FIX, XI and XII are significantly elevated in the presence of Mim8 and should not be performed. A chromogenic FIX assay could be used to accurately measure FIX activity in the presence of Mim8. There was some interference in the DRVVT method we used so local assessment of other DRVVT methods is advised. Differences in all other tests would not be predicted to affect patient management.

Von Willebrand factor assays in patients with acquired immune thrombotic thrombocytopenia purpura treated with caplacizumab.

Acquired immune thrombotic thrombocytopenic purpura (iTTP) is a rare disease with a poor prognosis if undiagnosed. It is caused by autoantibody production to the von Willebrand factor (VWF) cleaving protease, A disintegrin and metalloproteinase with a thrombospondin type 1 motif, member 13 (ADAMTS13). Caplacizumab, an immunoglobulin directed to the platelet glycoprotein Ibα receptor of VWF, has been reported to induce quicker resolution of iTTP compared to placebo. The laboratory measurement of VWF activity was significantly reduced in clinical trials of caplacizumab. Several VWF assays are available in the UK and this study investigated whether differences in VWF parameters were present in 11 patients diagnosed with iTTP and treated with daily caplacizumab. Chromogenic factor VIII activity, VWF antigen, collagen binding activity, VWF multimers and six VWF activity assays were measured prior to caplacizumab therapy and on several occasions during treatment. VWF antigen and collagen binding activity levels were normal or borderline normal in all patients. Ultra-large molecular weight multimers were present in all patients following treatment. VWF activity assays were normal or reduced during treatment, but this was reagent and patient dependant. In the unusual scenario of a caplacizumab-treated patient requiring measurement of VWF activity, it is important that laboratories understand how their local reagents perform as results cannot be predicted.

Laboratory coagulation tests and recombinant porcine factor VIII: A United Kingdom Haemophilia Centre Doctors' Organisation guideline.

INTRODUCTION: Acquired haemophilia A (AHA) is a rare bleeding disorder caused by development of auto-antibodies to endogenous coagulation factor VIII (FVIII). Recombinant porcine factor VIII (rpFVIII) is currently licensed only for the management of bleeding in patients with AHA. Regular monitoring of rpFVIII is recommended to assess treatment effectiveness. AIM: This guideline from the United Kingdom Haemophilia Centre Doctors' Organisation (UKHCDO) examines the current publications in the area and aims to offer advice for the laboratory monitoring of rpFVIII in patients with AHA. METHODS: A review of the current literature was undertaken followed by critical review by the authors. RESULTS/CONCLUSIONS: A validated one-stage clotting FVIII assay is recommended for the measurement and regular monitoring of rpFVIII. Assessment of cross-reacting rpFVIII inhibitors by one-stage porcine Bethesda assay should be performed as part of the initial diagnosis of AHA or prior to treatment with rpFVIII. Available data show that chromogenic FVIII assays underestimate rpFVIII and this should be considered if measurement of rpFVIII is required in patients receiving Emicizumab.

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.

Principles of care for acquired hemophilia.

OBJECTIVE: To establish clear priorities for the care of patients with acquired hemophilia A (AHA) by proposing 10 key principles of practical, holistic AHA management. METHOD: These principles were developed by the Zürich Haemophilia Forum, an expert panel of European hemophilia specialists comprising physicians and nursing and laboratory specialists. RESULTS: The 10 proposed principles for AHA care are as follows: (a) Improving initial diagnosis of AHA; (b) Differential diagnosis of AHA: laboratory assessment of patients with unusual bleeding; (c) Effective communication between laboratories, physicians, and specialists; (d) Improving clinical care: networking between healthcare professionals in the treating hospital and specialist hemophilia centers; (e) Comprehensive assessment of bleeding; (f) Appropriate use of bypassing agents; (g) Long-term follow-up and monitoring for efficacy and safety of immunosuppressive treatment; (h) Inpatient/outpatient settings; (i) Access to innovative and disruptive treatments; (j) Promotion of international collaborative research. CONCLUSION: The proposed principles for holistic AHA care aim to ensure swift diagnosis and optimal patient management. Key to achieving this goal is training for healthcare personnel in non-specialist hospitals and collaboration between different specialists. We hope these principles will increase awareness of AHA in the wider medical community and catalyze efforts toward improving its practical, multidisciplinary management.

Effects of emicizumab on APTT, one-stage and chromogenic assays of factor VIII in artificially spiked plasma and in samples from haemophilia A patients with inhibitors.

INTRODUCTION: Emicizumab (Hemlibra, Roche-Chugai) is a recombinant humanized bispecific IgG4 antibody which mimics some of the actions of activated factor VIII (FVIIIa) by binding to factor X (FX) and activated factor IX (FIXa) to activate FX. AIM: To evaluate the effect of emicizumab on the APTT, standard one-stage APTT-based FVIII activity assay (sOSA) using plasma calibrators, modified OSA (mOSA) using r2 Diagnostics emicizumab specific calibrator and chromogenic FVIII assays. Tests were performed on plasma artificially spiked with emicizumab and from four severe haemophilia A (SHA) patients treated with emicizumab. METHOD: APTT in spiked plasma was performed with 13 APTT reagents and in SHA patients with 5 reagents. OSA in spiked plasma was performed with 9 APTT reagents, 7 APTT reagents were used for OSA in SHA patients and six chromogenic substrate assays (CSA) were performed. RESULTS: In SHA, APTTs normalized after the first dose of emicizumab. At weeks 32/36 of treatment, the mean sOSA FVIII:C ranged from 2.47 IU/mL (Synthasil) to greater than 7.00 IU/mL with all other reagents. mOSA ranged from 59.8 µg/mL (Synthasil) to 74.5 µg/mL (APTT SP). Bovine CSA did not recover any FVIII:C activity. Hyphen Biomed human CSA, demonstrated FVIII activity when calibrated against a plasma calibrator. CONCLUSION: The APTT was significantly shortened in the presence of emicizumab. sOSA FVIII:C levels were erroneously high, and it is not recommended that these be performed. Quantification of emicizumab concentration was possible by mOSA. Human CSA was sensitive to emicizumab and surrogate FVIII:C activity could be determined. Bovine CSA were insensitive to emicizumab and could not be used to quantify emicizumab concentration.

Cross-reacting recombinant porcine FVIII inhibitors in patients with acquired haemophilia A.

INTRODUCTION: Acquired haemophilia A (AHA) is a rare bleeding disorder caused by the development of autoantibodies to endogenous human factor VIII (hFVIII). If treatment of bleeding is required, one option is recombinant porcine FVIII (rpFVIII). Cross-reactivity between factor VIII inhibitors and rpFVIII has previously been described. AIM: The aim of this study was to retrospectively assess the incidence of cross-reacting anti-porcine inhibitors in patients diagnosed with AHA in two UK centres. METHODS: The plasma of fifty-one patients diagnosed with AHA via reduced FVIII:C and positive FVIII inhibitor titre as detected with a Nijmegen-Bethesda assay (NBA) was also tested by a porcine Bethesda assay (PBA). The NBA was modified by replacement of human FVIII with rpFVIII in the PBA, with determination of residual FVIII by one-stage clotting assay. RESULTS: The median FVIII inhibitor titre by NBA was 22.8 BU/mL (range: 0.8-1000 BU/mL). 37% of samples exhibited linear, type 1 kinetics in the NBA. Negative PBA was observed in 26 patients, and 25 were positive (median PBA: 3.5 BU/mL; range: 0.8-120 BU/mL). Type 1 kinetics were observed in 40% of PBA-positive patients. At NBA tires of greater than 100 BU/mL, the positive predictive value for the presence of porcine cross-reactivity was 100%. At NBA below 5 BU/mL, the negative predictive value for the presence of porcine cross-reactivity was 71%. CONCLUSION: Cross-reactivity between FVIII inhibitors and rpFVIII was observed in 49% of patients. The presence of inhibitors to rpFVIII may influence the treatment choice for patients with acquired haemophilia A.

Laboratory measurement of factor replacement therapies in the treatment of congenital haemophilia: A United Kingdom Haemophilia Centre Doctors' Organisation guideline.

Assay discrepancies can occur with laboratory monitoring of FVIII and FIX replacement therapy, particularly for the extended half-life products. This guideline collates current published data and provides advice on appropriate choice of assays for laboratory measurement of replacement therapy for patients with Haemophilia A and B without inhibitors. It is recommended that each haemophilia centre should ensure that appropriate laboratory assays are available for FVIII and FIX products in local clinical use. Patient samples should be assayed against calibrators traceable to WHO Plasma International Standards. Assay discrepancies are common especially for the extended half-life FVIII and FIX products, and assays of these products may need to be verified with the specific CFC being used.

Laboratory coagulation tests and emicizumab treatment A United Kingdom Haemophilia Centre Doctors' Organisation guideline.

INTRODUCTION: The factor VIII mimetic emicizumab (Hemlibra, Hoffman-la Roche, Basel, Switzerland) has a novel mode of action that affects the laboratory monitoring of patients receiving this treatment. AIM: This guideline from the United Kingdom Haemophilia Centre Doctors Organisation (UKHCDO) aims to provide advice for clinical and laboratory staff on appropriate use of laboratory assays in patients with Haemophilia A treated with emicizumab. METHODOLOGY: The guideline was prepared by a review of the available literature and discussion and revision by the authors. RESULTS: The guideline describes the effect of emicizumab on commonly used coagulations tests and provides recommendations on the use of assays for measurement of factor VIII and factor VIII inhibitor in the presence of emicizumab. The guideline also provides recommendations on measurement of emicizumab. CONCLUSION: Knowledge of the effect of emicizumab on coagulation tests and factor assays is required to ensure appropriate testing and monitoring of therapy in patients receiving this drug.

Agreement between one stage and chromogenic assays in samples from patients receiving recombinant porcine FVIII (Obizur, Susoctocog-alfa).

INTRODUCTION: Recombinant porcine FVIII (rpFVIII) (Obizur, Susoctcog-alfa, Takeda, Japan) is licensed for the treatment of bleeding in acquired Haemophilia A (AHA). The summary of product characteristics state that monitoring should be by one stage assay (OSA) rather than chromogenic assay (CSA). CSA have been shown to underestimate activity when rpFVIII is added to plasma in vitro. METHODS: Samples from three AHA patients (n = 21) (pre- and post rpFVIII) were assessed using FVIII:C assays; OSA methods: Actin, Actin FS, Actin FSL and Pathromtin SL performed on CS5100i (Sysmex, Kobe, Japan); APTT-SP, SynthASil and SynthAFax performed on ACL TOP (Werfen, Barcelona, Spain). CSA methods on CS5100i: Siemens Chromogenic Assay, Biophen FVIII:C, Technochrom FVIII:C; on ACL TOP: Rox Factor VIII, Coamatic Factor VIII and CRYOcheck Factor VIII. RESULTS: OSA and CSA varied according to reagent used median OSA 61 IU/dL (range 41.5-81 IU/dL (ANOVA p < 0.0001)) median CSA 46.5 IU/dL (range of method specific medians 36.5-84 IU/dL (ANOVA p < 0.0001)). Amongst OSA, Actin FS was associated with the highest FVIII:C, APTT-SP was associated with the lowest. Variation in CSA results by different methods was also seen with highest FVIII:C levels obtained using the Technochrom FVIII:C and the lowest levels obtained with Siemens Assay. CONCLUSION: The relationship between OSA and CSA was not consistent between method or patient. Previously there has been reports of underestimation by CSA in in vitro spiked samples. Investigation into concentration of phospholipids in the APTT reagents may explain some of these variations.

Clinical Implications of Discrepancy between One-Stage Clotting and Chromogenic Factor IX Activity in Hemophilia B.

BACKGROUND: Discrepancy in factor IX activity (FIX:C) between one-stage assay (OSA) and chromogenic substrate assay (CSA) in patients with hemophilia B (PwHB) introduces challenges for clinical management. AIM: To study the differences in FIX:C using OSA and CSA in moderate and mild hemophilia B (HB), their impact on classification of severity, and correlation with genotype. METHODS: Single-center study including 21 genotyped and clinically characterized PwHB. FIX:C by OSA was measured using ActinFSL (Siemens) and CSA by Biophen (Hyphen). In addition, in vitro experiments with wild-type FIX were performed. Reproducibility of CSA was assessed between three European coagulation laboratories. RESULTS: FIX:C by CSA was consistently lower than by OSA, with 10/17 PwHB having a more severe hemophilia type by CSA. OSA displayed a more accurate description of the clinical bleeding severity, compared with CSA. A twofold difference between OSA:CSA FIX:C was present in 12/17 PwHB; all patients had genetic missense variants in the FIX serine protease domain. Discrepancy was also observed with diluted normal plasma, most significant for values below 0.10 IU/mL. Assessment of samples with low FIX:C showed excellent reproducibility of the CSA results between the laboratories. CONCLUSION: FIX:C was consistently higher by OSA compared with the CSA. Assessing FIX:C by CSA alone would have led to diagnosis of a more severe hemophilia type in a significant proportion of patients. Our study suggests using both OSA and CSA FIX:C together with genotyping to classify HB severity and provide essential information for clinical management.

Specific and global coagulation assays in the diagnosis of discrepant mild hemophilia A.

The activity of the factor VIII coagulation protein can be measured by three methods: a one or two-stage clotting assay and a chromogenic assay. The factor VIII activity of most individuals with mild hemophilia A is the same regardless of which method is employed. However, approximately 30% of patients show marked discrepancies in factor VIII activity measured with the different methods. The objective of this study was to investigate the incidence of assay discrepancy in our center, assess the impact of alternative reagents on factor VIII activity assays and determine the usefulness of global assays of hemostasis in mild hemophilia A. Factor VIII activity was measured in 84 individuals with mild hemophilia A using different reagents. Assay discrepancy was defined as a two-fold or greater difference between the results of the one-stage and two-stage clotting assays. Rotational thromboelastometry and calibrated automated thrombography were performed. Assay discrepancy was observed in 31% of individuals; 12% with lower activity in the two-stage assay and 19% with lower activity in the one-stage assay. The phenotype could not always be predicted from the individual's genotype. Chromogenic assays were shown to be a suitable alternative to the two-stage clotting assay. Thromboelastometry was found to have poor sensitivity in hemophilia. Calibrated automated thrombography supported the results obtained by the two-stage and chromogenic assays. The current international guidelines do not define the type of assay to be used in the diagnosis of mild hemophilia A and some patients could be misclassified as normal. In our study, 4% of patients would not have been diagnosed on the basis of the one-stage factor VIII assay. Laboratories should use both one stage and chromogenic (or two-stage) assays in the diagnosis of patients with possible hemophilia A.

The combination of emicizumab and recombinant factor VIII in plasma: Which assays can we use for accurate measurement?

INTRODUCTION: The bispecific antibody, emicizumab, is a prophylactic therapy used for the treatment of haemophilia A (HA). Patients may require additional replacement factor VIII (FVIII) to ensure adequate haemostasis. This study investigated the laboratory measurement of severe HA (SHA) plasma spiked with 36 combinations of emicizumab plus recombinant (r) FVIII concentrates. METHOD: FVIII assays were performed by one stage assay (OSA) using eight APTT reagents from three manufacturers and chromogenic assays (CSA) using seven kits. CSA kits comprised a range of bovine FX/FIXa, bovine FX/human FIXa or human FX/FIXa. Thrombin generation (TG) was assessed by CAT and ST-Genesia. RESULTS: Emicizumab-calibrated modified OSA and human FX CSA both overestimated rFVIII in the presence of emicizumab; median FVIII:C of up to 89% higher was observed in plasma spiked with both drugs compared to just rFVIII. In bovine FX CSA assays, there was a FVIII:C increase of up to 11% in plasmas spiked with both drugs compared to rFVIII alone. TG parameters were not all normalized by the presence of emicizumab however addition of rFVIII increased TG. ETP and peak thrombin were normalized at 50 µg/ml emicizumab using ST-Genesia but were still reduced at 75 µg/ml with CAT. Addition of rFVIII further normalized results. CONCLUSION: Modified OSA and human FX CSA could not distinguish between rFVIII or emicizumab. The presence of both emicizumab and rFVIII increased thrombin generation to normal levels compared to each drug alone. Bovine FX CSA can be used to accurately determine FVIII activity of rFVIII in plasma which also contains emicizumab.

The effect of a next generation factor VIII mimetic bispecific antibody (Mim8) on assays of factor VIII activity and thrombin generation.

BACKGROUND: Mim8 is a next generation bispecific antibody developed for the prophylactic treatment of hemophilia A. The sensitivity of activated plasma thromboplastin time (APTT), assays measuring factor VIII activity (FVIII:C) and thrombin generation to plasma containing Mim8 was assessed. METHODS: Congenital severe hemophilia A plasma was spiked with Mim8 at 0 µg/mL to 20 µg/mL. APTT was measured with 4 reagents, one-stage FVIII with 9 reagents, and chromogenic FVIII with 6 assays. Thrombin generation was assessed in a low tissue factor system. RESULTS: At 1-µg/mL Mim8, the APTT was shortened to within normal limits and one-stage FVIII:C was >1.00 IU/mL with all APTT reagents. Modified one-stage assays calibrated with Mim8 reference material calibrated recovered within 20% of the target Mim8 concentration with most APTT reagents. Factor VIII:C of bovine only chromogenic assays was <0.04 IU/mL at all Mim8 concentrations. Factor VIII:C of human only chromogenic assay was >4.00 IU/mL at 20-µg/mL Mim8. Factor VIII:C of hybrid bovine FX, human FIXa chromogenic assays ranged from 0.076 to >3.00 IU/mL at 20-µg/mL Mim8. Normal thrombin generation was restored at 5-µg/mL Mim8. CONCLUSIONS: APTT-based assays are sensitive to Mim8 and should not be performed in the presence of the drug. Chromogenic assays containing human proteins or hybrid human/bovine proteins demonstrated variable sensitivity to Mim8. Bovine only chromogenic assays were largely insensitive to the presence of Mim8. Thrombin generation normalized at increased Mim8 concentrations. Modified one-stage and chromogenic assays could be used to quantify the Mim8 concentration in plasma.

How to assess parallelism in factor assays: coefficient of variation of results with different dilutions or slope ratio?

INTRODUCTION: Non-parallelism in factor assays can lead to incorrect factor activities. Parallelism can be assessed by calculating the coefficient of variation (CV) of results obtained on 3 dilutions of the same sample. Some authors have proposed that if there is <15% then the average activity is reportable. Some analysers use a slope ratio (SR) to calculate parallelism, with an acceptance range of approximately 0.9-1.1. METHODS: We evaluated CV and SR in one stage FII-FXII assays on Sysmex CS5100i using Innovin or Actin FS. Frozen normal and pathological plasmas, plasmas containing Direct Oral Anticoagulants, Direct Thrombin Inhibitors or Lupus Anticoagulant were analysed to assess possible non-parallelism. RESULTS: In plasmas with factor levels >25 IU/dl (plus no interfering substances) all CVs were < 15%. One sample (low factor activities 10-15 IU/dl), had CVs > 15% in FII, FVII and FXII assays only. SR outside of 0.9-1.1 were seen in FII and FXII assays at different levels of clotting factor including some within the normal range. Non-parallelism was detected more frequently with SR than CV for those with interfering substances. CONCLUSIONS: SR outside of 0.9-1.1 were seen in different levels of clotting factors, including samples which did not contain interfering substances. The target of 15% CV was a better discriminator than a SR for acceptance. When factor levels were reduced to around 10-15 IU/dl, a target 20 %CV was more appropriate than 15%. It might be appropriate for laboratories to assess locally whether their acceptance criteria need to be wider at low levels of clotting factors.

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.