INTRODUCTION:About 40%-70% of persons with a clinically relevant bleeding tendency who are referred to haemostasis experts are classified as having a 'bleeding disorder of unknown cause' (BDUC) as no biological entity can be found after extensive laboratory testing. Currently, guidelines are under development regarding diagnostic assessment and management to minimize variation in clinical practice. AIM:Investigate current practices regarding BDUC in the Netherlands. METHODS:An online survey on the best BDUC definition, associated bleeding phenotype, clinical and diagnostic approaches, treatment, registration, and follow-up was distributed amongst healthcare providers working in Dutch haemophilia treatment centres (HTCs). RESULTS:The survey was completed by 39/54 (72%) respondents. Twenty percent did not register BDUC patients in their HTC. Healthcare professionals indicated that follow-up should depend on bleeding phenotype severity and bleeding history, and other potential causes for an increased bleeding tendency should be excluded. Moreover, the use of laboratory tests within the routine diagnostic pathway was demonstrated to be heterogeneous. Regarding treatment, tranexamic acid was most frequently prescribed for minor and major surgical interventions (79% and 86%), dental extractions (93%) and childbirth (93%). Desmopressin was prescribed for major surgical procedures by 79%. CONCLUSION:Our survey shows that Dutch current practice varies but is generally in line with recent ISTH SSC recommendations. Additionally, it describes other clinically relevant topics not included in the international survey, such as follow-up and exclusion of other causes for bleeding. This survey therefore adds to international efforts to unify BDUC definition, diagnostic approach, treatment and follow-up, and to attain broadly supported guidelines.

Desmopressin (DDAVP) can be used to prevent or stop bleeding. However, large inter-individual variability is observed in DDAVP response and determinants are largely unknown. In this systematic review and meta-analysis we aim to identify the response to DDAVP, and the factors that determine DDAVP response in patients. We included studies with patients with any bleeding disorder receiving DDAVP. First and second screening round and risk of bias assessment were performed by independent reviewers. The main outcome was proportion of patients with complete (factor level > 50 U/dL), or partial (30-50 U/dL) response to DDAVP. Determinants of response including disease type, age, sex, Von Willebrand factor (VWF) and factor VIII (FVIII) mutations, and baseline factor levels were investigated. In total, 591 articles were found and 103 were included. Of these, 71 articles (1772 patients) were suitable for the study's definition of response. Meta-analysis showed a pooled response proportion of 0·71 [0·64;0·78] and a significant difference in response between disease subtypes. For hemophilia A, baseline FVIII:C was a borderline significant determinant of response. In von Willebrand disease (VWD) type 1 patients, VWF:Ag, VWF:Act and FVIII:C were significant determinants. A large variation in response was observed for specific mutations in VWF and F8. Response to DDAVP varied between disease subtypes, and was largely determined by the baseline levels of FVIII:C for hemophilia A and VWF:Ag for VWD. Our findings highlight the significant differences in response and emphasize the need for a standardized response definition and further research into response mechanisms.

Pharmacokinetic (PK)-guided dosing of factor concentrates in patients with haemophilia A is generally recommended for the optimisation of prophylac- tic treatment. PK-guided dosing can also be useful in the perioperative setting, where guidelines advise to keep factor VIII (FVIII) activity levels within tight target ranges to prevent bleeding. Previous studies suggest changes in FVIII PK following medical procedures as well as potential time-dependent effects, meaning that population PK models specific to the perioperative setting are required. In this study, we use data from haemophilia A patients collected during the prophylactic and perioperative setting to identify covariates that explain changes in FVIII PK. Additionally, we use machine learning methods to find potential time-dependent effects on FVIII clearance. Perioperative FVIII clearance was generally lower compared to the prophylactic setting. Covariates related to the complexity of the medical procedures were correlated to larger decreases in clearance. Importantly, subjects undergoing more complex procedures also depicted potentially relevant time-dependent effects on clearance. These effects could be highly variable between subjects. Directly using PK parameters obtained from the prophylactic setting resulted in relatively high mean absolute percentage error (MAPE) at 26.3\%, while the perioperative model including time-dependent effects depicted markedly reduced error (10.3\%). The presence of high variability between subjects and potential time-dependent effects complicates the selection of optimal dosing regimens before the start of medical procedures. Our method can be used to optimise treatment in real-time, but close monitoring of FVIII levels will likely remain necessary. ### Competing Interest Statement The authors have declared no competing interest. ### Funding Statement This project was performed as part of the SYMPHONY consortium, which has received funding from the Netherlands Organisation for Scientic Research (NWO) under grant agreement NWA.1160.18.038. ### Author Declarations I confirm all relevant ethical guidelines have been followed, and any necessary IRB and/or ethics committee approvals have been obtained. Yes The details of the IRB/oversight body that provided approval or exemption for the research described are given below: Medisch-Ethische Toetsingscommissie of Amsterdam University Medical Centers waived ethical approval for this work I confirm that all necessary patient/participant consent has been obtained and the appropriate institutional forms have been archived, and that any patient/participant/sample identifiers included were not known to anyone (e.g., hospital staff, patients or participants themselves) outside the research group so cannot be used to identify individuals. Yes I understand that all clinical trials and any other prospective interventional studies must be registered with an ICMJE-approved registry, such as ClinicalTrials.gov. I confirm that any such study reported in the manuscript has been registered and the trial registration ID is provided (note: if posting a prospective study registered retrospectively, please provide a statement in the trial ID field explaining why the study was not registered in advance). Yes I have followed all appropriate research reporting guidelines, such as any relevant EQUATOR Network research reporting checklist(s) and other pertinent material, if applicable. Yes All model code is made available at https://github.com/JanssenaPerioperativeFVIII.

Hemocompatibility-related adverse events (HRAEs), particularly gastrointestinal bleeding, remain a frequent complication after left ventricular assist device (LVAD) implantation. The current study sought to describe and analyze whether early (<60 days) postoperative von Willebrand factor (VWF) activity assays predict the risk of gastrointestinal bleeding and stroke. A prospective single-center study including 74 HeartMate 3 device recipients between 2016 and 2023 was undertaken. The postoperative trajectory of the VWF profile was analyzed using linear mixed-effect models and Cox models were used to quantify associations between an early postoperative dip (≤0.7) in VWF activity assay measurements and late outcomes. Preoperatively, the mean VWF:Activity (Act)/Antigen (Ag) and VWF:Collagen Binding (CB)/Ag ratios were 0.94 (95% confidence interval [CI] = 0.81–1.02) and 0.95 (95% CI = 0.80–1.03), respectively, decreasing to 0.66 (95% CI = 0.57–0.73) and 0.67 (95% CI = 0.58–0.74) within 40 days (p < 0.05). In patients with VWF:CB/Ag and VWF:Act/Ag ratios ≤0.7 significantly more gastrointestinal bleeding (hazard ratio [HR]: 2.53; 95% CI = 1.1–5.8, and HR: 3.7; 95% CI = 1.5–9.2, respectively) and hemorrhagic stroke events (HR: 3.5; 95% CI = 1.6–7.6 and HR: 4.9; 95% CI = 2.1–11.7, respectively) were observed throughout the entire late (>60 days) postoperative period. In patients with VWF:Act/Ag ratio ≤0.7 less ischemic stroke events were observed (HR: 0.11; 95% CI = 0.01–0.85). In conclusion, VWF:Act/Ag and VWF:CB/Ag ratios ≤0.7 in the early postoperative phase can be used as biomarkers to predict HRAEs during long-term LVAD support.

In more than half of the individuals with a clinically relevant bleeding tendency who are referred to hemostasis experts, no biological etiology can be found after extensive laboratory testing. These persons are diagnosed with an unexplained bleeding tendency or “bleeding disorder of unknown cause” (BDUC). The mucocutaneous bleeding phenotype of individuals with BDUC is generally comparable to that of individuals with inherited bleeding disorders such as von Willebrand disease or platelet function disorders. BDUC definitions applied in literature are heterogeneous, but all comprise 2 main criteria: (1) there is an increased bleeding tendency based on the clinical view of the physician and/or an increased bleeding score; (2) no abnormalities are found with available hemostasis laboratory tests. This is reflected in the recent published BDUC definition by the Scientific and Standardization Committee of the International Society on Thrombosis and Haemostasis, stating that BDUC is a diagnosis of exclusion, characterized by normal hemostatic investigations despite a clinically significant bleeding tendency. Importantly, other nonhemostatic and acquired causes of bleeding should be excluded, but details on exclusion criteria and associated diagnostic testing remain undefined. Patients and health care providers are challenged by the uncertainty and lack of formal diagnosis particularly as there is no clear consensus regarding treatment. Research on the diagnostic value of new laboratory tests in individuals with BDUC has not yet been productive. In this illustrative review, the current practice and knowledge gaps in BDUC are addressed, previous research on BDUC is outlined and future directions with outstanding questions for future research in BDUC are highlighted.

BACKGROUND:Endothelial colony-forming cells (ECFCs) derived from patients can be used to investigate pathogenic mechanisms of vascular diseases like von Willebrand disease. Considerable phenotypic heterogeneity has been observed between ECFC clones derived from healthy donors. This heterogeneity needs to be well understood in order to use ECFCs as endothelial models for disease. OBJECTIVES:Therefore, we aimed to determine phenotypic and gene expression differences between control ECFCs. METHODS:A total of 34 ECFC clones derived from 16 healthy controls were analyzed. The transcriptome of a selection of ECFC clones (n = 15) was analyzed by bulk RNA sequencing and gene set enrichment analysis. Gene expression was measured in all ECFC clones by quantitative polymerase chain reaction. Phenotypic profiling was performed and migration speed of the ECFCs was measured using confocal microscopy, followed by automated quantification of cell morphometrics and migration speed. RESULTS:Through hierarchical clustering of RNA expression profiles, we could distinguish 2 major clusters within the ECFC cohort. Major differences were associated with proliferation and migration in cluster 1 and inflammation and endothelial-to-mesenchymal transition in cluster 2. Phenotypic profiling showed significantly more and smaller ECFCs in cluster 1, which contained more and longer Weibel-Palade bodies. Migration speed in cluster 1 was also significantly higher. CONCLUSION:We observed a range of different RNA expression patterns between ECFC clones, mostly associated with inflammation and clear differences in Weibel-Palade body count and structure. We developed a quantitative polymerase chain reaction panel that can be used for the characterization of ECFC clones, which is essential for the correct analysis of pathogenic mechanisms in vascular disorders.

Background Gray Platelet Syndrome (GPS) patients with Neurobeachin-like 2 (NBEAL2) deficiency produce platelets lacking alpha-granules (AGs) and present with lifelong bleeding symptoms. AGs are lysosome-related organelles (LROs) and store the hemostatic protein Von Willebrand factor (VWF) and the transmembrane protein P-selectin. Weibel-Palade bodies (WPBs) are LROs of endothelial cells and also store VWF and P-selectin. In megakaryocytes, NBEAL2 links P-selectin on AGs to the SNARE protein SEC22B on the endoplasmic reticulum (ER), thereby preventing premature release of cargo from AG precursors. In endothelial cells, SEC22B drives VWF trafficking from ER to Golgi and promotes the formation of elongated WPBs, but it is unclear if this requires NBEAL2. Objectives To investigate a potential role for NBEAL2 in WPB biogenesis and VWF secretion using NBEAL2 deficient endothelial cells. Methods Interaction of SEC22B with NBEAL2 in endothelial cells was investigated by interactomic mass spectrometry and pull down analysis. Endothelial Colony Forming Cells (ECFCs) were isolated from healthy controls and 3 unrelated GPS patients with mutations in NBEAL2 . Results We show that SEC22B binds to NBEAL2 in ECs. GPS patient-derived ECFCs are deficient of NBEAL2, but reveal normal formation and maturation of WPBs and normal WPB cargo recruitment. Neither basal nor histamine-induced VWF secretion are altered in the absence of NBEAL2. Conclusions While NBEAL2 deficiency causes absence of AGs in GPS patients, it has no impact on WPB functionality in ECs. Our data highlight the difference in regulatory mechanisms between these two hemostatic storage compartments. Essentials We characterized Gray Platelet Syndrome patient-derived endothelial cells with biallelic NBEAL2 mutations ex vivo . NBEAL2 is not essential for Weibel-Palade body biogenesis, maturation, and Von Willebrand factor secretion from endothelial cells.

Background To account for interindividual variability in the pharmacokinetics (PK) of factor concentrates, PK-guided dosing is increasingly implemented in haemophilia patients. Calculations are based on provided label potency, but legislation allows a potency difference of +/- 20% between label and actual potency. It is unknown if these differences affect PK guidance. Aim Explore the effects of potency differences on individual factor VIII (FVIII) PK parameters and the prediction of FVIII trough levels of dosing regimens. Methods We analyzed individual preoperative PK profiling data from severe and moderate haemophilia A patients included in the OPTI-CLOT randomized controlled trial. Label and actual potency were compared, with data on potency provided by pharmaceutical companies. For both potencies, individual PK parameters were estimated and concentration-time curves were constructed by nonlinear mixed-effects modelling. Finally, we explored the effect of both the identified and the maximum legislated potency difference on predicted FVIII trough levels infused in a low and high dose regimen. Results In 45/50 included patients, actual potency was higher than its label potency. The median potency difference was 6.0% (range -9.2% to 18.4%) and resulted in varying individual PK parameter estimates but practically identical FVIII concentration-time curves. As expected, predicted FVIII trough levels were linearly correlated to the actual dose. Conclusion It is not necessary to take potency differences into account when applying PK guidance of FVIII concentrates in haemophilia A patients. However, when the patient is switched to another FVIII batch after PK-guided dosing, trough levels may deviate +/- 20% from calculations based on label dose.

HaemophiliaVolume 28, Issue 4 p. e109-e112 LETTER TO THE EDITOR Diagnostic evaluation of the first macroscopic haematuria episode in adult haemophilia patients Lorenzo G.R. Romano, Corresponding Author Lorenzo G.R. Romano [email protected] Department of Hematology, Hemophilia Treatment Center, Erasmus MC, Erasmus University Medical Center, Rotterdam, The Netherlands Correspondence Lorenzo G.R. Romano, Erasmus University Medical Center, Wytemaweg 80, 3015 CN Rotterdam, the Netherlands. Email: [email protected]Search for more papers by this authorGreta Mulders, Greta Mulders Department of Hematology, Hemophilia Treatment Center, Erasmus MC, Erasmus University Medical Center, Rotterdam, The NetherlandsSearch for more papers by this authorSara C.M. Stoof, Sara C.M. Stoof Department of Hematology, Hemophilia Treatment Center, Erasmus MC, Erasmus University Medical Center, Rotterdam, The NetherlandsSearch for more papers by this authorIris van Moort, Iris van Moort Department of Hematology, Hemophilia Treatment Center, Erasmus MC, Erasmus University Medical Center, Rotterdam, The NetherlandsSearch for more papers by this authorMartijn B. Busstra, Martijn B. Busstra Department of Urology, Erasmus MC, Erasmus University Medical Center, Rotterdam, The NetherlandsSearch for more papers by this authorFrank W.G. Leebeek, Frank W.G. Leebeek Department of Hematology, Hemophilia Treatment Center, Erasmus MC, Erasmus University Medical Center, Rotterdam, The NetherlandsSearch for more papers by this authorMarieke J.H.A. Kruip, Marieke J.H.A. Kruip Department of Hematology, Hemophilia Treatment Center, Erasmus MC, Erasmus University Medical Center, Rotterdam, The NetherlandsSearch for more papers by this author Lorenzo G.R. Romano, Corresponding Author Lorenzo G.R. Romano [email protected] Department of Hematology, Hemophilia Treatment Center, Erasmus MC, Erasmus University Medical Center, Rotterdam, The Netherlands Correspondence Lorenzo G.R. Romano, Erasmus University Medical Center, Wytemaweg 80, 3015 CN Rotterdam, the Netherlands. Email: [email protected]Search for more papers by this authorGreta Mulders, Greta Mulders Department of Hematology, Hemophilia Treatment Center, Erasmus MC, Erasmus University Medical Center, Rotterdam, The NetherlandsSearch for more papers by this authorSara C.M. Stoof, Sara C.M. Stoof Department of Hematology, Hemophilia Treatment Center, Erasmus MC, Erasmus University Medical Center, Rotterdam, The NetherlandsSearch for more papers by this authorIris van Moort, Iris van Moort Department of Hematology, Hemophilia Treatment Center, Erasmus MC, Erasmus University Medical Center, Rotterdam, The NetherlandsSearch for more papers by this authorMartijn B. Busstra, Martijn B. Busstra Department of Urology, Erasmus MC, Erasmus University Medical Center, Rotterdam, The NetherlandsSearch for more papers by this authorFrank W.G. Leebeek, Frank W.G. Leebeek Department of Hematology, Hemophilia Treatment Center, Erasmus MC, Erasmus University Medical Center, Rotterdam, The NetherlandsSearch for more papers by this authorMarieke J.H.A. Kruip, Marieke J.H.A. Kruip Department of Hematology, Hemophilia Treatment Center, Erasmus MC, Erasmus University Medical Center, Rotterdam, The NetherlandsSearch for more papers by this author First published: 20 May 2022 https://doi.org/10.1111/hae.14590Read the full textAboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onEmailFacebookTwitterLinkedInRedditWechat REFERENCES 1Ghosh K. JF, Mohanty D. Haematuria and urolithiasis in patients with haemophilia. Eur J Haematol. 2003; 70(6): 410-2. 2Kulkarni R. MSJ, Evatt B., Hemophilia surveillance system project investigators. Renal disease among males with haemophilia. Haemophilia. 2003; 9(6): 703-10. 3Beck P. EK. Renal abnormalities in patients with hemophilia and Christmas disease. Clin Radiol. 1972; 23(3): 349-54. 4Prentice CR, Lindsay RM, Barr RD, Forbes CD, Kennedy AC, McNicol GP, et al. Renal complications in haemophilia and Christmas disease. Q J Med. 1971; 40(157): 47-61. 5Holme PA, Combescure C, Tait RC, Berntorp E, Rauchensteiner S, de Moerloose P, et al. Hypertension, haematuria and renal functioning in haemophilia—a cross-sectional study in Europe. Haemophilia. 2016; 22(2): 248-55. 6Srivastava A, Santagostino E, Dougall A, Kitchen S, Sutherland M, Pipe SW, et al. WFH guidelines for the Management of Hemophilia, 3rd edition. Haemophilia. 2020. 7Kaiser Permanente Southern California. Standardized hematuria evaluation clinical reference (guideline). 2012. 8van der Molen AJ, Hovius MC. Hematuria: a problem-based imaging algorithm illustrating the recent Dutch guidelines on hematuria. Am J Roentgenol. 2012; 198(6): 1256-65. 9Quon DV, Konkle BA. How we treat: haematuria in adults with haemophilia. Haemophilia. 2010; 16(4): 683-5. 10Avidor Y, Nadu A, Matzkin H. Clinical significance of gross hematuria and its evaluation in patients receiving anticoagulant and aspirin treatment. Urology. 2000; 55(1): 22-4. Volume28, Issue4July 2022Pages e109-e112 ReferencesRelatedInformation

Von Willebrand disease (VWD) is a bleeding disorder caused by quantitative (type 1 or 3) or qualitative (type 2A/2B/2M/2N) defects of circulating von Willebrand factor (VWF). Circulating VWF levels not always fully explain bleeding phenotypes, suggesting a role for alternative factors, like platelets. Here, we investigated platelet factor 4 (PF4) in a large cohort of patients with VWD. PF4 levels were lower in type 2B and current bleeding phenotype was significantly associated with higher PF4 levels, particularly in type 1 VWD. Based on our findings we speculate that platelet degranulation and cargo release may play a role across VWD subtypes.

BACKGROUND:Treatment choices for individual patients with an inborn bleeding disorder are increasingly challenging due to increasing options and rising costs for society. We have initiated an integrated interdisciplinary national research programme.OBJECTIVES:The SYMPHONY consortium strives to orchestrate personalized treatment in patients with an inborn bleeding disorder, by unravelling the mechanisms behind inter-individual variations of bleeding phenotype.PATIENTS:The SYMPHONY consortium will investigate patients with an inborn bleeding disorder, both diagnosed and not yet diagnosed.RESULTS:Research questions are categorized under the themes: 1) Diagnosis; 2) Treatment; and 3) Fundamental research and consist of workpackages addressing specific domains. Importantly, collaborations between patients and talented researchers from different areas of expertise promise to augment the impact of the SYMPHONY consortium, leading to unique interactions and intellectual property.CONCLUSIONS:SYMPHONY will perform research on all aspects of care, treatment individualization in patients with inborn bleeding disorders as well as diagnostic innovations and results of molecular genetics and cellular model technology with regard to the hemostatic process. We believe that these research investments will lead to health care innovations with long-term clinical and societal impact. This consortium has been made possible by a governmental, competitive grant from the Netherlands Organization for Scientific Research (NWO) within the framework of the NWA-ORC Call grant agreement NWA.1160.18.038.

Background Dosing of replacement therapy with factor VIII concentrate in patients with haemophilia A in the perioperative setting is challenging. Underdosing and overdosing of factor VIII concentrate should be avoided to minimise risk of perioperative bleeding and treatment costs. We hypothesised that dosing of factor VIII concentrate on the basis of a patient's pharmacokinetic profile instead of bodyweight, which is standard treatment, would reduce factor VIII consumption and improve the accuracy of attained factor VIII levels. Methods In this open-label, multicentre, randomised, controlled trial (OPTI-CLOT), patients were recruited from nine centres in Rotterdam, Groningen, Utrecht, Nijmegen, The Hague, Leiden, Amsterdam, Eindhoven, and Maastricht in The Netherlands. Eligible patients were aged 12 years or older with severe or moderate haemophilia A (severe haemophilia was defined as factor VIII concentrations of <0.01 IU/mL, and moderate haemophilia as 0.01-0.05 IU/mL), without factor VIII inhibitors, and planned for elective low or medium risk surgery as defined by surgical risk score. Patients were randomly assigned (1:1) using a web-based randomisation system and treatment minimisation, stratified by method of administration of factor VIII concentrate (continuous infusion vs bolus administration) and risk level of surgery (low and medium risk surgery), to the pharmacokinetic-guided or standard treatment group. The primary endpoint was total amount of infused factor VIII concentrate (IU per kg bodyweight) during perioperative period (from day of surgery up to 14 days after surgery). Analysis was by intention to treat and the safety analysis population comprised all participants who underwent surgery with factor VIII concentrate. This study is registered with the Netherlands Trial Registry, NL3955, and is now closed to accrual. Findings Between May 1, 2014, and March 1, 2020, 98 patients were assessed for eligibility and 66 were enrolled in the trial and randomly assigned to the pharmacokinetic-guided treatment group (34 [52%]) or the standard treatment group (32 [48%]). Median age was 49.1 years (IQR 35.0 to 62.1) and all participants were male. No difference was seen in consumption of factor VIII concentrate during the perioperative period between groups (mean consumption of 365 IU/kg [SD 202] in pharmacokinetic-guided treatment group vs 379 IU/kg [202] in standard treatment group; adjusted difference -6 IU/kg [95% CI -88 to 100]). Postoperative bleeding occurred in six (18%) of 34 patients in the pharmacokinetic-guided treatment group and three (9%) of 32 in the standard treatment group. One grade 4 postoperative bleeding event occurred, which was in one (3%) patient in the standard treatment group. No treatment-related deaths occurred. Interpretation Although perioperative pharmacokinetic-guided dosing is safe, it leads to similar perioperative factor VIII consumption when compared with standard treatment. However, pharmacokinetic-guided dosing showed an improvement in obtaining factor VIII concentrations within the desired perioperative factor VIII range. These findings provide support to further investigation of pharmacokinetic-guided dosing in perioperative haemophilia care. Copyright (C) 2021 Elsevier Ltd. All rights reserved.

We explored the effects of extreme weight loss after gastric bypass surgery on factor VIII concentrate pharmacokinetic (PK) parameters in a patient with haemophilia A. We present a 32-year-old man with severe haemophilia A, with a body mass index (BMI) of 42.6 kg/m2who underwent laparoscopic sleeve gastrectomy. We showed that a population PK model with ideal body weight as morphometric variable instead of bodyweight led to an adequate description of the individual PKs in this patient with a variable BMI. Strikingly, no differences were observed in the individual PK parameters after extreme weight loss. Therefore, the resulting extreme weight loss after surgery did not lead to prophylactic dose changes in this patient with severe haemophilia. We carefully conclude that population PK–pharmacodynamic models are still obligatory to give more insight into functional effects of significant weight loss on the haemostatic balance.

Factor (F) VIII deficiency causes bleeding in haemophilia A patients because of the reduced formation of procoagulant enzyme thrombin, which is needed to make the blood clot. We measured the dynamics of coagulation in haemophilia A patients by measuring thrombin generation (TG). Additionally, we quantified the procoagulant process of prothrombin conversion and anticoagulant process of thrombin inhibitor complex formation. In haemophilia A, prothrombin conversion is severely reduced, causing TG to be low. Nevertheless, the thrombin inactivation capacity of these patients is comparable to that in healthy subjects, leading to a severe imbalance between procoagulant and anticoagulant processes and a subsequent increased bleeding risk. A novel therapy in haemophilia A is the targeting of anticoagulant pathway, e.g. thrombin inhibitor antithrombin (AT), to restore the haemostatic balance. We simulated the effect of AT reduction on TG in silico. Lowering AT levels restored TG dose-dependently and an AT reduction of 90–95% led to almost normal TG in most patients . However, the variation in response to AT reduction was large between patients, indicating that this approach should be tailored to each individual patients. Ideally, TG and thrombin dynamics simulation could in the future contribute to the management of patients undergoing AT targeting therapy.

Aims Under‐ and, especially, overdosing of replacement therapy in haemophilia A patients may be prevented by application of other morphometric variables than body weight (BW) to dose factor VIII (FVIII) concentrates. Therefore, we aimed to investigate which morphometric variables best describe interindividual variability (IIV) of FVIII concentrate pharmacokinetic (PK) parameters. Methods PK profiling was performed by measuring 3 FVIII levels after a standardized dose of 50 IU kg −1 FVIII concentrate. A population PK model was constructed, in which IIV for clearance (CL) and central volume of distribution (V1) was quantified. Relationships between CL, V1 and 5 morphometric variables (BW, ideal BW [IBW], lean BW, adjusted BW, and body mass index [BMI]) were evaluated in normal weight (BMI < 25 kg m −2 ), overweight (BMI 25–30 kg m −2 ) and obese haemophilia A patients (BMI > 30 kg m −2 ). Results In total, 57 haemophilia A patients (FVIII≤0.05 IU mL −1 ) were included with median BW of 83 kg (range: 53–133) and median age of 48 years (range: 18–77). IBW best explained observed variability between patients, as IIV for CL and V1 was reduced from 45.1 to 37.6 and 26.% to 14.1%, respectively. CL, V1 and half‐life were similar for all BMI categories. The national recommended dosing schedule did not result in adequate trough levels, both in case of dosing based on BW and IBW. However, dosing based on IBW prevented unnecessary high FVIII peaks. Conclusion IBW is the most suitable morphometric variable to explain interindividual FVIII PK variability and is more appropriate to dose overweight and obese patients.

Background von Willebrand factor (VWF) is crucial for optimal dosing of factor VIII (FVIII) concentrate in hemophilia A patients as it protects FVIII from premature clearance. To date, it is unknown how VWF behaves and what its impact is on FVIII clearance in the perioperative setting. Aim To investigate VWF kinetics (VWF antigen [VWF:Ag]), VWF glycoprotein Ib binding (VWF:GPIbM), and VWF propeptide (VWFpp) in severe and moderate perioperative hemophilia A patients included in the randomized controlled perioperative OPTI-CLOT trial. Methods Linear mixed effects modeling was applied to analyze VWF kinetics. One-way and two-way analyses of variance were used to investigate perioperative VWFpp/VWF:Ag ratios and associations with surgical bleeding. Results Fifty-nine patients with median age of 48.8 years (interquartile range: 34.8-60.0) were included. VWF:Ag and VWF:GPIbM increased significantly postoperatively. Blood type non-O or medium risk surgery were associated with higher VWF:Ag and VWF:GPIbM levels compared with blood type O and low risk surgery. VWFpp/VWF:Ag was significantly higher immediately after surgery than 32 to 57 hours after surgery (p < 0.001). Lowest VWF:Ag quartile (0.43-0.92 IU/mL) was associated with an increase of FVIII concentrate clearance of 26 mL/h (95% confidence interval: 2-50 mL/h) compared with highest VWF antigen quartile (1.70-3.84 IU/mL). VWF levels were not associated with perioperative bleedingF(4,227) = 0.54,p = 0.710. Conclusion VWF:Ag and VWF:GPIbM levels increase postoperatively, most significantly in patients with blood type non-O or medium risk surgery. Lower VWF antigen levels did not lead to clinically relevant higher FVIII clearance. VWF:Ag or VWF:GPIbM levels were not associated with perioperative hemorrhage.

Diagnosis, treatment monitoring and assessment of desmopressin effect in haemophilia A patients are performed by measurement of factor VIII activity (FVIII). The two assays commonly applied are the one‐stage assay and the chromogenic assay. Especially in non‐severe haemophilia A, discrepancies between these assays are common. It is still unestablished which assay corresponds best with bleeding phenotype and desmopressin effect.