Thrombin Generation Assay Research Articles

Thrombin generation after prothrombin complex concentrate or plasma transfusion during cardiac surgery.

Thrombin generation (TG) is reduced after cardiac surgery using cardiopulmonary bypass (CPB), contributing to coagulopathy and bleeding. Plasma transfusion or four-factor prothrombin complex concentrate (PCC) are commonly used to treat coagulopathic bleeding after CPB without knowledge of how each may restore TG. To determine the effect of PCC infusion on restoration of thrombin generation compared with plasma transfusion, we performed a laboratory-based secondary analysis of a randomized, controlled trial of adult patients undergoing cardiac surgery to assess efficacy and safety of 4F-PCC versus plasma for treatment of perioperative coagulopathic bleeding after CPB. Participants were randomized to receive either PCC (15 IU/kg) or plasma (10-15ml/kg) after separation from CPB. Participant blood samples were obtained at pre-specified serial timepoints, with laboratory assays for TG and factor levels subsequently performed. The primary outcome was change in thrombin generation (TG) parameters after each randomized treatment through postoperative day 5. Secondary outcomes included serially derived clotting factor levels. Of 100 randomized participants, 99 were included in this laboratory analysis (PCC group, N = 51; plasma group, N = 48). After treatment, participants in the PCC group compared with those in the plasma group showed higher endogenous thrombin potential (ETP, Median, Interquartile range, IQR: 688 [371-1069] vs. 1088 [550-1691] nM minutes, P = 0.01), a greater increase din ETP (P = 0.002) and peak TG (P = 0.01) in the timepoints between heparin reversal and after treatment administration. Both groups demonstrated similar values in all TG assays by postoperative day 1 (P > 0.05). The PCC group also demonstrated higher levels of proteins C, S, and Factors II, VII, IX and X, early after treatment (P < 0.001 for all comparisons). Antithrombin levels were initially higher in the plasma group after treatment (Median, IQR: 66% [61-71%] vs. 56% [51-65%], P = 0.002) but differences did not persist beyond postoperative day 3. In this laboratory analysis from a recent randomized trial in adult cardiac surgery, PCC administration restored thrombin generation more rapidly than plasma in the early postoperative period without laboratory evidence of hypercoagulability. ClinicalTrials.gov identifier: NCT02557672 [1].

Andexanet Alfa-Associated Heparin Resistance in Cardiac Surgery: Mechanism and In Vitro Perspectives.

Andexanet alfa (andexanet) is the only Food and Drug Administration-approved antidote for direct FXa (factor Xa) inhibitors but has been reported to cause resistance to unfractionated heparin (UFH). This has delayed anticoagulation for procedures requiring cardiopulmonary bypass. The mechanism, andexanet and UFH dose dependence, and thrombotic risk of andexanet-associated heparin resistance are unknown. The effect of andexanet in vitro was determined using activated clotting times and thromboelastography. Ex vivo cardiopulmonary bypass circuits were used to determine whether andexanet impaired anticoagulation for extracorporeal circulation. Kinetics of AT (antithrombin) inhibition of FXa and thrombin were measured in the presence of andexanet. Equilibrium modeling and thrombin generation assay validation were used to predict the role of andexanet, AT, and UFH concentrations in andexanet-associated heparin resistance. Andexanet prevented UFH-mediated prolongation of activated clotting times and thromboelastography times. At lower concentrations of andexanet, heparin resistance could be overcome with suprapharmacologic doses of UFH, but not at higher andexanet concentrations. Andexanet rendered standard doses of UFH inadequate to prevent circuit thrombosis, and suprapharmacologic UFH doses were only partially able to overcome this. Scanning electron microscopy demonstrated coagulation activation in circuits. Andexanet prevented UFH enhancement of AT-mediated inhibition of FXa and thrombin. Equilibrium modeling and thrombin generation assay validation demonstrated that andexanet creates a triphasic equilibrium with UFH and AT: initial UFH unresponsiveness, normal UFH responsiveness when andexanet is depleted, and finally AT depletion. Sufficient cardiopulmonary bypass heparinization can only occur at low therapeutic andexanet doses and normal AT levels. Higher andexanet doses or AT deficiency may require high UFH doses and potentially AT supplementation. Andexanet causes heparin resistance due to redistribution of UFH-bound AT. If andexanet cannot be avoided before heparinization and direct thrombin inhibitors are undesirable, our in vitro study suggests excess UFH should be considered as a potential strategy before AT supplementation.

Impact of sample processing delays on plasma markers of inflammation, chemotaxis, cell death, and blood coagulation.

Biosampling studies in critically ill patients traditionally involve bedside collection of samples followed by local processing (ie. centrifugation, aliquotting, and freezing) and storage. However, community hospitals, which care for the majority of Canadian patients, often lack the infrastructure for local processing and storage of specimens. A potential solution is a "simplified" biosampling protocol whereby blood samples are collected at the bedside and then shipped to a central site for processing and storage. One potential limitation of this approach is that delayed processing may alter sample characteristics. To determine whether delays in blood sample processing affect the stability of cytokines (IL-6, TNF, IL-10, IFN-γ), chemokines (IL-8, IP-10, MCP-1, MCP-4, MIP-1α, MIP-1β), cell-free DNA (cfDNA) (released by dying cells), and blood clotting potential in human blood samples. Venous blood was collected into EDTA and citrate sample tubes and stored at room temperature (RT) or 4°C for progressive intervals up to 72 hours, prior to processing. Plasma cytokines and chemokines were quantified using single or multiplex immunoassays. cfDNA was measured using Picogreen DNA Quantification. Blood clotting potential was measured using a thrombin generation assay. Blood samples were collected from 9 intensive care unit (ICU) patients and 7 healthy volunteers. Admission diagnoses for the ICU patients included sepsis, trauma, ruptured abdominal aortic aneurysm, intracranial hemorrhage, gastrointestinal bleed, and hyperkalemia. After pre-processing delays of up to 72 hours at RT or 4°C, no significant changes were observed in plasma cytokines, chemokines, cfDNA, or thrombin formation. Delayed sample processing for up to 72 hours at either RT or 4°C did not significantly affect cytokines, chemokines, cfDNA, or blood clotting potential in plasma samples from healthy volunteers and ICU patients. A "simplified" biosampling protocol is a feasible solution for conducting biosampling research at hospitals without local processing capacity.

Factor X consumption attenuates the coagulation effect of emicizumab: a case of severe hemophilia A treated with emicizumab and factor VIII-bypassing agents.

In patients with hemophilia A with inhibitor (PwHA-I), emicizumab drastically reduces bleeding events. However, few studies have investigated the behavior and effects of factor X (FX) in patients who require intensive treatment with factor VIII-bypassing agents (BPA) and emicizumab. A 59-year-old man with HA-I receiving emicizumab prophylaxis was admitted to our hospital because of acute gangrenous cholecystitis. He received percutaneous transhepatic gallbladder drainage and laparoscopic cholecystectomy along with repeated administration of recombinant activated factor VII (rFVIIa). On day 10, a large hematoma developed around the residual gallbladder. Rotational thromboelastometry (ROTEM) suggested poor effect of rFVIIa and reduced activity of emicizumab. Considering that this could be due to consumption of FX, plasma-derived FVIIa/FX agent (pdFVIIa/X) was administered, and ROTEM parameters recovered considerably. The patient was discharged on day 19 uneventfully. Plasma assays revealed that FX antigen level (FX:Ag) was 107.5% at baseline but then decreased. Administration of pdFVIIa/FX restored FX:Ag (pre/post 47.2%/125.5%). ROTEM and thrombin generation assay with in vitro addition of anti-emicizumab antibody suggested that low FX:Ag was responsible for attenuating the effect of emicizumab, and pdFVIIa/FX administration restored coagulation potentials. In PwHA-I receiving intensive treatment with rFVIIa under emicizumab prophylaxis, FX consumption might attenuate the effect of emicizumab.

The in vitro cross-reactivity and blood coagulation potential of recombinant porcine factor VIII in Japanese patients with acquired hemophilia A.

Recombinant porcine factor VIII (rpFVIII) is a hemostatic agent for acquired hemophilia A (AHA). Cross-reaction of auto-antibodies against rpFVIII has been reported, although no data are available in Japanese patients. This study investigated the cross-reactivity and coagulation potential of rpFVIII in plasma samples from Japanese patients with AHA. Cross-reactivity was calculated as the ratio of anti-porcine FVIII inhibitor titer (pFVIII-INH) to human FVIII inhibitor titer. Comprehensive coagulation potential was assessed by clot waveform analysis (CWA) and thrombin generation assay (TGA) in samples spiked with rpFVIII (equivalent to 200 U/kg). Nine of 16 plasma samples (56.3%) had positive pFVIII-INH, with a median cross-reactivity of 1.2%. FVIII activity (FVIII:C) was restored to > 100% in all samples upon spiking with rpFVIII, but was weakly correlated with pFVIII-INH. CWA parameters and most TGA parameters were restored to normal upon spiking with rpFVIII; correlation of these parameters with FVIII:C was similar to that observed in controls. Overall, cross-reactivity to rpFVIII in Japanese patients was similar to that reported in Caucasian patients. Our results suggest that an initial clinical dose of 200 U/kg rpFVIII could restore coagulation potential to normal, and that FVIII:C monitoring after rpFVIII administration may be more informative than pFVIII-INH before administration.

Plasma apixaban levels and thrombin generation assay in patients with atrial fibrillation with dose reduction criteria of apixaban

Abstract Background Off-label reduced-dose apixaban is commonly prescribed in patients with atrial fibrillation (AF). However, the pharmacokinetic data of apixaban according to the dosage and label is limited especially in those with dose reduction criteria of apixaban. Purpose We investigated the apixaban plasma concentration (PC) and thrombin generation assay (TGA) parameters across different apixaban dose settings. Methods We enrolled 398 non-valvular AF patients with more than single-dose reduction criteria of apixaban and divided them into three groups: (1) on-label standard dose (single dose-reduction criterion with standard-dose of apixaban 5mg twice daily, n=173); (2) off-label reduced-dose (single dose-reduction criterion with apixaban 2.5mg twice daily, n=61); and (3) on-label reduced-dose (two or more dose-reduction criteria with apixaban 2.5mg twice daily, n=164). Apixaban PC by anti-Xa assay and TGA parameters of these three groups were compared at the trough level. Results The on-label standard dose group showed a higher PC than the on-label reduced dose (124.7 vs. 80.3 ng/mL, p&amp;lt;0.001), and the on-label reduced dose exhibited a higher PC than the off-label reduced dose (80.3 vs. 53.2 ng/mL, p=0.031) (Figure). The TGA parameters displayed a similar pattern of differences, with the on-label standard dose group tends to show the least thrombogenic profiles (Figure). Lower creatinine clearance (CrCl), older age, and female sex were statistically significant predictors for a higher apixaban PC by multivariable regression model (p&amp;lt;0.001, p=0.043, and 0.023, respectively), and CrCl was the most influential variable to dichotomize apixaban PC in all three groups (Figure). Conclusions Off-label reduced-dose apixaban group exhibited significantly lower apixaban level than both on-label standard dose and on-label reduced-dose apixaban groups, suggesting the importance of adhering to current dose-reduction criteria for maintaining appropriate apixaban levels. Caution is particularly advised in off-label under-dosing for patients with high creatinine clearance. Further investigation into the impact of off-label under-dosing on clinical outcomes is essential to guide optimal therapeutic strategies.

Preclinical characterisation and first-in-human results on the tolerability and pharmacodynamic effect of REGN9933, a monoclonal antibody targeting the factor XI/activated factor XI apple 2 domain

Abstract Background/Introduction Standard-of-care anticoagulants are associated with increased bleeding risk. Genetic/pharmacological data suggest coagulation factor XI (FXI) inhibition can prevent thrombosis with minimal increased bleeding risk. We present preclinical and first-in-human (FIH) data on REGN9933, a FXI-binding monoclonal Ab. Purpose To characterise REGN9933 epitope binding sites, affinities for FXI and activated FXI (FXIa), and effect on high molecular weight kininogen (HMWK)’s interaction with FXI. Also, to assess safety, tolerability and pharmacodynamics in healthy human participants (pts). Methods Epitope binding sites mapped with cryogenic electron microscopy, binding affinities determined with plasmon resonance techniques, effect on thrombin generation assessed with a thrombin generation assay, and impact on HMWK:FXI interaction analysed using ELISAs. In the FIH, Ph 1, randomised, double-blind, single-centre study, pts received a single dose of REGN9933 intravenously (IV; 3–300 mg) or subcutaneously (SC; 100 mg &amp; 300 mg), or placebo (PBO). Primary endpoint: incidence and severity of treatment-emergent AEs (TEAEs). Other endpoints: effect of REGN9933 on activated partial thromboplastin time (aPTT) and prothrombin time (PT) to assess intrinsic and extrinsic pathway-triggered coagulation, respectively; and FXI activity. Results REGN9933 was found to bind the FXI apple 2 domain, with subnanomolar binding affinities for FXI and FXIa at 37°C, resulting in reduced thrombin generation from the intrinsic (not extrinsic) pathway. REGN9933 competed with HMWK for FXI binding in a dose-related manner. In the Ph 1 study, 56 pts received REGN9933 (IV, n=30; SC, n=12) or PBO (n=14); 42.9% and 21.4% had ≥1 TEAE, respectively (most common with REGN9933: headache, 12%; oropharyngeal pain, 5%). No serious/severe TEAEs, or TEAEs of special interest (inc. moderate/severe bleeding) reported. Laboratory tests revealed no clinically meaningful differences in the number/type of treatment-emergent potentially clinically significant values with REGN9933 vs PBO. REGN9933 resulted in dose-dependent prolongation of aPTT; aPTT mean fold change from baseline was highest with IV 300 mg after 8 hrs (2.7) and remained &amp;gt;2 for 36 days (Fig 1). There was no detectable effect on PT or clinically meaningful effect on bleeding time. REGN9933 supressed FXI activity in a dose-dependent manner, with suppression to approx. the lower limit of assay quantification (5%) with IV ≥30 mg (Fig 2). Conclusion(s) REGN9933 binds the FXI apple 2 domain and inhibits HMWK:FXI interaction, preventing intrinsic pathway-triggered FXI activation. FIH data showed dose-dependent inhibition of the intrinsic coagulation pathway by REGN9933, without affecting the extrinsic or common pathways. Pharmacodynamic and safety findings support continued development of REGN9933 as an anticoagulant that may carry less bleeding risk than currently approved agents.

Increased thrombin generation in kidney transplant recipients with donor-specific antibodies directed against human leukocyte antigens.

The development of de novo anti-HLA donor specific antibodies (DSAs) is associated with poor outcomes in kidney transplant recipients. It is surmised that an interaction between DSAs and the graft endothelium cause tissue injury, however, the exact underlying pathomechanism and optimal management of patients with DSAs remain undetermined. We hypothesized that in kidney transplant recipients the presence of DSAs induce hemostasis alterations, including hypercoagulability, as assessed by the thrombin generation assay (TGA). Patients and methods. In this observational cohort study, 27 kidney transplant recipients with DSAs (DSA+ group) and 16 without DSAs (DSA- group) were enrolled. Venous blood samples were obtained, and besides routine laboratory tests, von Willebrand factor antigen (VWF), FVIII activity, soluble E selectin (sEsel), soluble P selectin (sPsel), TGA, clot lysis assay (CLA), complement levels (C3, C4) were measured. To correlate results with potential changes in DSA status over time, patients were followed and reassessed 6 ± 1.5 months later. VWF and sPsel did not differ between groups, but both parameters were increased in the majority of patients. Endogenous thrombin potential (ETP) was significantly higher in the DSA+ group as compared to DSA- patients (median:1666; IQR:1438-2012 vs. 1230; IQR:1097-1659 nM*min, p=0.0019). Follow-up measurements indicated that the observed hemostasis alterations were not transient. CLA parameters, C3 and C4 did not differ between DSA+ and DSA- groups. The extent of anti-HLA II DSA positivity correlated positively with ETP, while tacrolimus levels negatively correlated with ETP and VWF/FVIII levels. In patients with anti-HLA class II DSAs, thrombin generation was significantly increased as compared to DSA- kidney transplant recipients, suggesting that the presence of antibodies is associated with hypercoagulability. Tacrolimus levels were negatively associated with TGA parameters. Hypercoagulability, associated with the presence of DSAs, may potentially contribute to the pathomechanism of antibody-mediated graft injury, warranting future prospective studies.

A novel γ-chain mutation p.Asp318His in a Chinese family with dysfibrinogenemia.

Congenital dysfibrinogenemia is characterized by reduced fibrinogen activity, but normal immunoreactive fibrinogen levels. Here, we present a novel case with an elevated risk of thrombosis. Coagulation assays, gene analysis, in silico tools, sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE), fibrin polymerization, thrombin generation assay, and electron microscopy scanning were utilized to elucidate the pathogenic mechanism. The proband manifested with a normal immunologic fibrinogen (2.13 g/l) but reduced functional fibrinogen (0.39 g/l). Subsequent genetic analysis unveiled a novel heterozygous mutation, c.1030G>C (p.Asp318His), in the γ-chain D domain of fibrinogen, which was highly conserved in homologous species and led to enhanced thrombin generation capability. The ability of the proband's fibrinogen to polymerize was significantly impaired, with decreased final turbidity. Scanning electron microscopy indicated that the fibers of the proband were thinner than normal, with smaller pores. Thromboelastography (TEG) results demonstrated prolonged K time, decreased angle value, and a normal confidence interval value in the proband. We present a novel case displaying the γAsp318His mutation, which resulted in dysfibrinogenemia.

Thrombin generation assay in COVID-19 patients shows a hypocoagulable pattern

Patients with COVID-19 often exhibit coagulopathy, which can significantly impact prognosis. Therefore, investigating coagulation in this context is clinically relevant. The thrombin generation assay (TGA) provides comprehensive data on individual clotting patterns. In our study, we utilized a calibrated automated thrombogram to globally assess coagulation in COVID-19 patients. The study included 67 COVID-19 patients (40 hospitalized in the medical ward and 27 in intensive care units) and 45 blood donors for comparison. Our analysis revealed significant differences in TGA parameters (lag time, time-to-peak, thrombin peak, and endogenous thrombin potential) between patients and blood donors, suggesting a hypocoagulable state in the former. Specifically, COVID-19 patients exhibited prolonged lag time and time-to-peak values, as well as lower thrombin peak and endogenous thrombin potential compared to blood donors (Mann-Whitney test: p&lt;0.05); notably, no significant differences in thrombin generation were observed based on the clinical setting. These findings suggest a reduced capacity for thrombin generation, indicating a consumptive coagulopathy in COVID-19 patients and that in this context, thrombosis is primarily attributable to localized effects in the lungs, platelet activation, and/or prothrombotic endothelial dysfunction. The thrombin generation assay is instrumental in defining coagulation patterns in COVID-19 and may also be applicable to other infectious diseases.

The anticoagulant effects of milvexian, a novel small molecule factor XIa inhibitor, are neutralized by activated prothrombin complex concentrates and recombinant factor VIIa in human plasma and whole blood in vitro

BackgroundThe development of anticoagulants that provide antithrombotic efficacy without a concomitant bleeding risk remains an unmet clinical need in thrombosis. Although direct oral anticoagulants (DOACs) have a reduced incidence of major bleeding compared with warfarin, they still carry a bleeding risk, resulting in a suboptimal therapeutic index. Epidemiologic data suggest that inhibiting activated factor (F)XI may offer an improved safety profile with respect to bleeding risk compared with current-generation DOACs. Additionally, a phase II trial of milvexian in patients undergoing elective total knee replacement demonstrated robust dose-dependent efficacy with no statistically significant increase in bleeding. Nevertheless, the ability to rapidly and effectively correct FXIa inhibitor–induced anticoagulation may still be important in situations where patients experience uncontrolled bleeding or require emergency surgery. ObjectivesWe assessed the ability to normalize the anticoagulant effects of the novel small molecule FXIa inhibitor milvexian (BMS-986177/JNJ-70033093) in vitro using commercially available prohemostatic agents. MethodsMilvexian-associated anticoagulation and correction was evaluated in activated partial thromboplastin time clotting assays, thromboelastography, and kaolin-initiated thrombin generation assays. ResultsActivated prothrombin complex concentrates (PCCs) and recombinant factor (rF)VIIa corrected the anticoagulant effects of milvexian in activated partial thromboplastin time clotting assays, thromboelastography, and kaolin-initiated thrombin generation assays. In contrast, other agents including PCCs, rFIX, and rFVIII demonstrated either modest or no correction of milvexian-associated anticoagulation. ConclusionThis study demonstrated that currently available activated PCCs and rFVIIa normalize anticoagulation induced by milvexian in vitro. The clinical utility of these agents remains to be established.

Thrombin generation to evaluate the complex hemostatic balance of hemophilia A plasma containing direct oral anticoagulant and supplemented by factor VIII

BackgroundThe incidence of cardiovascular diseases is increasing in persons with hemophilia A (HA). Therefore, anticoagulant therapy based on direct oral anticoagulants (DOACs) may be needed, despite the bleeding risk. In case of surgery or bleeding, such patients may be concomitantly treated with emicizumab (routine prophylaxis), factor (F)VIII products, and DOAC. Their concomitant presence constitutes a hemostatic challenge. Recent international guidelines stated that data are scarce on the hemostatic balance of plasma samples from patients with HA receiving emicizumab and DOAC. ObjectivesThe aim of this observational study was to assess the coagulation of FVIII-deficient plasma spiked with DOAC and emicizumab and to evaluate the effects of FVIII addition. MethodsProthrombin time, activated partial thromboplastin time, and thrombin generation (TG) using the calibrated automated thrombogram method were evaluated in aliquots of a commercial severe HA plasma supplemented with emicizumab (0, 12.5, 25, 50, and 100 ng/mL), DOAC (0, 50, 100, 200, and 400 ng/mL of apixaban, rivaroxaban, edoxaban, or dabigatran) and FVIII (0%, 5%, 15%, 50%, and 100%). ResultsDOAC rapidly induced a TG decrease. Emicizumab could counter this effect only for the lowest DOAC dose. FVIII addition to the FVIII-deficient plasma containing a DOAC and emicizumab improved TG and countered the anticoagulant effect of DOAC at ≤100 ng/mL. ConclusionOur findings indicate that FVIII can be safely used with emicizumab to counter the anticoagulant effect of DOAC at ≤100 ng/mL. The TG assay is an efficient tool to monitor plasma containing anti-FXa DOAC, but not dabigatran (anti-FIIa).

Enhanced venous thrombosis and hypercoagulability in murine and human metabolic dysfunction-associated steatohepatitis

BackgroundPatients with metabolic dysfunction-associated steatohepatitis (MASH) are at an increased risk of developing venous thromboembolic events, including deep vein thrombosis (DVT). To date, the study of DVT in MASH has been hampered by the lack of reliable models that mimic the pathologic aspects of human disease. ObjectivesTo evaluate DVT severity and hypercoagulability in murine and human MASH. MethodsTranscriptional changes in the liver, plasma markers of coagulation, and DVT severity were evaluated in mice fed a standard chow diet or a high-fructose, high-fat, and high-cholesterol MASH diet for 24 weeks. Plasma analyses of coagulation markers and thrombin generation assays were performed in a well-characterized cohort of patients with or without MASH. ResultsMice fed the MASH diet developed steatohepatitis and fibrosis, mimicking human MASH. Liver RNA sequencing revealed a significant upregulation of pathways related to inflammation and coagulation concomitant with increased levels of plasma coagulation markers including increased prothrombin fragment 1+2, thrombin-antithrombin complex, plasminogen activator inhibitor-1 levels, and endothelin 1. MASH exacerbated DVT severity in mice, as evidenced by increased thrombus weight and higher thrombosis incidence (15/15 vs 11/15 in controls, P = .0317). Higher endothelin 1 release and increased apoptosis were found in endothelial cells stimulated with supernatants of palmitate-stimulated HepG2 cells. Patients with MASH exhibited increased levels of plasma coagulation markers and delayed thrombin generation. ConclusionWe report enhanced DVT severity and hypercoagulability, both in murine and human MASH. Our model of MASH-DVT can facilitate a better understanding of the fundamental mechanisms leading to increased venous thromboembolic events in patients with MASH.

Plasma apixaban concentrations and thrombin generation assay parameters in response to dose reduction for atrial fibrillation.

To investigate plasma apixaban concentrations and thrombin generation assay (TGA) parameters across different apixaban doses in atrial fibrillation patients who had dose-reduction criteria for apixaban. This observational study included 374 patients (mean age 75.6 ± 7.7 years, 54.8% female) with dose-reduction criteria for apixaban. The patients were divided into 3 groups: (i) on-label standard dose (5 mg twice daily, n =166); (ii) on-label reduced dose (2.5 mg twice daily, n =55); and (iii) off-label underdose (2.5 mg twice daily, n =153). Apixaban concentrations determined via the anti-Xa assay and TGA parameters were compared at trough levels. The off-label underdose group exhibited significantly lower apixaban trough concentrations than the on-label reduced-dose and standard-dose groups (56.7 ± 42.9 vs. 83.7 ± 70.4 vs. 129.9 ± 101.8 ng/mL, all P <.001). Less than 70% of all patients fell within the expected range of apixaban concentrations. Proportions exceeding the upper limit of the expected range were significantly lower in the off-label underdose group (1.3%) than in the on-label reduced-dose (9.1%, P =.005) and standard-dose (12.7%, P <.001) groups. The TGA parameters showed the on-label standard-dose group displaying the lowest thrombogenic profiles. Lower creatinine clearance was the most significant predictor of higher apixaban concentrations. Off-label underdosed apixaban resulted in lower apixaban concentrations than both on-label standard and reduced-dose regimens. A considerable proportion of the patients exhibited apixaban concentrations outside the expected range, suggesting the potential benefits of plasma concentration monitoring. Further studies are needed to compare dosages directly, investigate the impact of plasma apixaban concentration monitoring and validate the current dose-reduction criteria.

An Inhibitory Single-Domain Antibody against Protein Z-Dependent Protease Inhibitor Promotes Thrombin Generation in Severe Hemophilia A and FXI Deficiency.

Protein Z-dependent protease inhibitor (ZPI) is an anticoagulant serpin that targets factor Xa (FXa) in the presence of protein Z (PZ), and factor XIa (FXIa). In factor-VIII-deficient mice, PZ or ZPI gene knock-out mitigates the bleeding phenotype, and pharmacological inhibition of PZ enhances thrombin generation in plasma from patients with hemophilia. To develop a single-domain antibody (sdAb) directed against ZPI to inhibit its anticoagulant activity. We screened for anti-ZPI sdAbs in a llama-derived phage display immune library of sdAbs. The sdAbs that bound ZPI were produced and purified for characterization. The binding of sdAbs to ZPI or other serpins was evaluated using ELISAs, and ZPI inhibition was measured in an anti-FXa or anti-FXIa chromogenic assay. The sdAbs's procoagulant activity was assessed in a thrombin generation assay in normal plasma, factor VIII- and FXI-deficient plasma. Of the four sdAbs found to bind to ZPI, one (referred to as ZPI-sdAb2) dose-dependently inhibited ZPI's anti-FXa and anti-FXIa activities with a mean half-maximal inhibitory concentration of 1.8 and 1.3 µM, respectively. ZPI-sdAb2 did not cross-react with other plasma serpins, such as antithrombin and α1-antitrypsin. ZPI-sdAb2 induced a significant increase in thrombin generation in plasma samples from healthy donors, patients with severe hemophilia A, and patients with FXI deficiency. ZPI-sdAb2 is the first specific, direct ZPI inhibitor found to exhibit procoagulant activity in plasma. This sdAb might have potential as a treatment for hemophilia or other bleeding disorders.

Coagulation disorders in liver cirrhosis - Diagnostics and management

Patients with liver cirrhosis often exhibit complex alterations in their hemostatic system that can be associated with both bleeding and thrombotic complications. While prophylactic correction of abnormal coagulation parameters should be avoided, an individualized approach is recommended prior to invasive procedures, whereby specific preventive measures to stabilize hemostasis should be based on the periprocedural bleeding risk. While the haemostatic system of patients with compensated cirrhosis is often in a rebalanced haemostatic state due to a parallel decline in both pro- and anti-haemostatic factors, a decompensation of liver cirrhosis can lead to destabilization of this fragile equilibrium. Since conventional coagulation tests do not adequately capture the complex changes in the hemostatic system in cirrhosis, functional analysis methods such as viscoelastic tests or thrombin generation assays can be used for evaluating the coagulation status. This review describes the underlying pathophysiological changes in the hemostatic system in liver cirrhosis, provides an overview of diagnostic methods and discusses therapeutic measures in case of bleeding and thrombotic complications.

Predelivery Haemostatic Biomarkers in Women with Non-Severe Postpartum Haemorrhage.

Background: Postpartum haemorrhage (PPH) is a frequent complication of childbirth that is difficult to predict. Predelivery coagulation biomarkers may help to guide preventive strategies. Our objective was to evaluate the association of predelivery haemostatic biomarkers with non-severe PPH. Methods: A nested case-control study was conducted within the « Study of Biological Determinants of Bleeding Postpartum » in order to compare different haemostatic biomarkers in plasma from pregnant women with non-severe PPH (cases) and controls without PPH matched for age, body mass index, term, and mode of delivery. Blood was collected at entry in the delivery room. Global haemostatic assays (thrombin generation assay (TGA) and plasmin generation assay (PGA)) were then performed on freshly thawed aliquots of platelet-poor plasma. Results: A total of 370 pregnant women (185 cases and 185 controls) were included. Median [interquartile range] predelivery platelet count was lower in PPH cases than in controls (217 [181-259] versus 242 [196-280] G/L). TGA and PGA parameters were similar between cases and controls. In a subset analysis of vaginal deliveries (n = 144), median predelivery TGA thrombin peak was lower, and median predelivery PGA lag phase was longer in cases compared to controls. In multivariable analysis, only predelivery platelet count was independently associated with non-severe PPH. Conclusions: Predelivery platelet count is associated with non-severe PPH. Differences in other haemostatic parameters are tenuous, questioning their usefulness in predicting non-severe PPH.

P-275 Advanced hemostasis assessment in endometriosis: strengthening confidence in the safety of hormonal treatments

Abstract Study question Are women with endometriosis in a state of systemic imbalance between pro- and anti-coagulants? Summary answer Women with endometriosis do not seem to exhibit a coagulation imbalance, at least at a systemic level. What is known already A state of platelet hyperactivation potentially leading to a hypercoagulation status has been described in women with endometriosis. This phenomenon could induce an altered local environment, promoting platelet-mediated paracrine changes in endometrial tissue and also increasing cardiovascular risk, which could be worsened by the use of estrogen dependent hormonal treatments. However, despite a slight difference in some coagulation parameters has been observed between women affected and controls, their levels remain, generally, within the normal reference range. Study design, size, duration This prospective case-control study including 101 women seeking infertility consultation at the Infertility Unit of Fondazione IRCCS Ca’ Granda Ospedale Maggiore Policlinico, Milano between January and July 2023 aimed to assess hemostasis function beyond traditional coagulation parameters. Participants/materials, setting, methods Blood of women with endometriosis (n = 51) or tubal or male factor infertility (controls; n = 50) was obtained before any ART treatment, and a complete panel of coagulation tests were performed, including basic parameters (aPTT, PT, FVIII, FII, PC, AT, FIV-C, DD, vWF, ADMT) as well as more sophisticated ones, such as Thrombin Generation Assay and Thromboelastometry, providing data on endogenous thrombin potential (ETP), clot formation time (CFT) and maximal clot firmness (MCF). Main results and the role of chance There were no significant differences between cases and controls in terms of age (37 [34-39] vs 36 [33-39]; p = 0.53, respectively) and smoking habits (14% vs 28%; p = 0.14, respectively). Women affected had a lower BMI compared to controls (22.7 [20.9-24.9] vs 21.4 [19.6-23.8]; p = 0.03), as it is usually expected. Results from TGA were expressed as ETP ratio (with-/without- thrombomodulin), and high ones were indicative of thrombomodulin resistance, taken as indexes of procoagulant imbalance; however, it was not different between women with and without the disease (0.75 [0.65-0.82] vs 0.75 [0.66-0.82]; p = 0.82, respectively). Other markers of procoagulant imbalance evaluated by thromboelastometry were also similar between cases and controls, including CFT (66 sec [58-78] vs 65 sec [59-79]; p = 0.69, respectively) and MCF (65 mm [62-68] vs 66mm [63-68]; p = 0.95, respectively). Considering the vWF/ADAMTS13 ratio, recently proposed to be altered in endometriosis, no difference was seen between affected and no-affected women (0.95 [0.76-1.14] vs 0.91 [0.68-1.15]; p = 0.41, respectively). Finally, all the basic coagulation parameters were also similar between groups. Limitations, reasons for caution Our sample size does not allow us to perform sub-analyses regarding the type of endometriosis, although we cannot exclude differences according to the various manifestations of the disease. Also, not having a systemic haemostasis imbalance does not exclude the possibility of local coagulation imbalances. Wider implications of the findings An altered systemic haemostasis could be worsened by the use of hormonal treatments. Our result indicating that there is no coagulation imbalance at a systemic level reassures about the absence of further contraindications to hormonal drugs as a treatment for endometriosis. Trial registration number not applicable

Utility of Global Hemostatic Assays in Patients with Bleeding Disorders of Unknown Cause.

Bleeding disorder of unknown cause (BDUC) is a diagnosis of exclusion after exhaustive evaluation of plasmatic coagulation and platelet function. This review explores the utility of global hemostatic assays as confirmatory tests and in elucidating the pathophysiology of BDUC. Unlike traditional hemostatic tests that focus on coagulation factors, global assays are conducted both in plasma and also whole blood. These assays provide a more comprehensive understanding of the cell-based model of coagulation, aid in the identification of plasmatic factor abnormalities that may reduce hemostatic capacity, and allow for the assessment of impaired platelet-endothelial interactions under shear stress, as well as hyperfibrinolytic states. While clinical tests such as skin bleeding time and global assays such as PFA-100 exhibit limited diagnostic capacity, the role of viscoelastic testing in identifying hemostatic dysfunction in patients with BDUC remains unclear. Thrombin generation assays have shown variable results in BDUC patients; some studies demonstrate differences compared with healthy controls or reference values, whereas others question its clinical utility. Fibrinolysis assessment in vitro remains challenging, with studies employing euglobulin clot lysis time, plasma clot lysis time, and fluorogenic plasmin generation yielding inconclusive or conflicting results. Notably, recent studies suggest that microfluidic analysis unveils shear-dependent platelet function defects in BDUC patients, undetected by conventional platelet function assays. Overall, global assays might be helpful for exploring underlying hemostatic impairments, when conventional hemostatic laboratory tests yield no results. However, due to limited data and/or discrepant results, further research is needed to evaluate the utility of global assays as screening tools.

Monoclonal whole IgG impairs both fibrin and thrombin formation: hemostasis and surface plasmon resonance studies.

Monoclonal gammopathies frequently associate with hemostatic alterations. Thrombotic events occur with high incidence particularly upon treatment, while in rarer cases hemorrhagic diathesis can be observed. Thepathology of these tendencies could be caused by thrombocytopenia or hyperviscosity burden of circulating monoclonal antibodies. Studies also suggest interference ofmonoclonal antibodies with primary hemostasis. We isolated monoclonal whole IgG paraproteins from two myeloma patients to observe their effect on thrombin formation and fibrin polymerization. Monoclonal whole IgG was prepared from sera of two newly diagnosed untreated multiple myeloma patients and control normal plasma samples. Fibrin formation was measured using thrombin time and dilute prothrombin time tests and thrombin formation was detected with a fluorimetric thrombin generation assay. In addition, molecular interactions were investigated by surface plasmon resonance (SPR). Thrombin time was prolonged upon addition of monoclonal IgG even at 30 g/L by 12 %, increasing up to 36 % at 60 g/L concentration. Dilute prothrombin time was prolonged by 20 % even at 30 g/L. Thrombin generation assay indicated an impairment in thrombin formation at the presence of monoclonal IgG compared to polyclonal at equivalent concentration. By an SPR assay we determined that both clonality IgG preparations interacted with fibrinogen, however interaction with human thrombin was only detected with monoclonal immunoglobulins (KD=1.03×10-7 M). Here we provide evidence that isolated monoclonal whole IgG from myeloma patients can impair both fibrin and thrombin formation and we demonstrate by SPR assay that it interacts with components of the final phase of the coagulation system.