Thrombin generation estimates the anticoagulation effect of direct oral anticoagulants with significant interindividual variability observed

Exploring the effects of Factor Xa inhibitors on thrombin generation in people with haemophilia

Optimal management of cardiovascular disease (CVD) in people with haemophilia (PWH) is a growing issue, given the continuing improvement in life expectancy among PWH. The evolving treatment paradigms targeting higher trough levels and the advent of non-factor replacement therapies (NFRT) means much of the 'protection' PWH were thought to have against CVD may be lost. There is a paucity of evidence regarding the safety of using anticoagulants in PWH. We designed a study assessing the thrombin generation (TG) of PWH of different severities and treatments, compared to non-haemophilia patients receiving a Factor Xa (FXa) inhibitor (apixaban or rivaroxaban), healthy controls, and assessing TG parameters of adding FXa inhibitor to the plasma of PWH receiving emicizumab prophylaxis. In total, 40 patients were included. TG was initiated with 5pM tissue factor (TF) using the calibrated automated thrombinoscope. Compared to those with mild haemophilia, patients receiving a FXa inhibitor had higher endogenous thrombin potential (ETP) (1278.42 vs 1831.36) and velocity index (40.71 vs 112.56), but both had a similar peak height (154.0 vs 262.63) and time to peak (both 5.83). People with severe haemophilia receiving emicizumab had significantly improved TG parameters compared to those not receiving emicizumab - ETP 1678.11 vs 809.96 and peak height 233.8 vs 92.05; however, when FXa inhibitor was added their TG parameters deteriorated to the severe haemophilia range (ETP 1179.60 and peak height 103.05). TG may provide additional useful information regarding the use of anticoagulants in PWH.

DOAC-associated bleeding, hemostatic strategies, and thrombin generation assays - a review of the literature

Direct oral anticoagulants (DOACs) account for most oral anticoagulant use. DOAC-associated bleeding events are commonly encountered in clinical practice and are associated with substantial morbidity and mortality. Both specific reversal agents and nonspecific hemostatic therapies, such as prothrombin complex concentrates, are used in the management of DOAC-associated bleeding. Measuring hemostatic efficacy and demonstrating a clinical impact from these therapies among studies of bleeding patients is challenging. Thrombin generation assays provide information on the total hemostatic potential of plasma, and have emerged as a promising modality to both measure the impact of DOACs on coagulation and to evaluate the effects of hemostatic therapies among patients with DOAC-associated bleeding. The mechanisms by which nonspecific hemostatic agents impact coagulation and thrombin generation in the context of DOAC therapy are unclear. As a result, we undertook a review of the literature using a systematic search strategy with the goal of summarizing the effects of DOACs on thrombin generation and the effects of both specific reversal agents and nonspecific hemostatic therapies on DOAC-altered thrombin generation parameters. We sought to identify clinical studies focusing on whether altered thrombin generation is associated with clinical bleeding and whether correction of altered thrombin generation parameters predicts improvements in clinical hemostasis. Lastly, we sought to outline future directions for the application of thrombin generation assays toward anticoagulation therapies and the question of anticoagulation reversal.

DOAC-stop can remove direct oral anticoagulants and allow analysis by global coagulation assays

INTRODUCTION

Activated charcoal based compounds such as DOAC-stop™ (DS) have been developed to remove direct oral anticoagulant (DOAC) interference in-vitro. However, few studies have used this approach with global coagulation assays (GCAs), such as thrombin generation assays, which are sensitive to the effect of DOACs.

METHODS

Thrombin generation with and without thrombomodulin (TM) via the automated ST-Genesia system, and the overall haemostatic potential (OHP) assay, a spectrophotometric fibrin generation assay in which fibrin formation (triggered by small amounts of thrombin (overall coagulation potential, OCP)) and fibrinolysis (by the addition of thrombin and tissue plasminogen activator) were measured on (i) pooled normal plasma (PNP) spiked with varying amounts of rivaroxaban, apixaban, and dabigatran, and (ii) platelet poor plasma (PPP) from 21 non-anticoagulated adults, before and after DS addition.

RESULTS

Following the addition of DS to spiked PNP without thrombomodulin, thrombin and velocity index increased by 21.9% and 42.6%, respectively, while ETP increased by 6.93%. A decrease in OCP (-10.6%) and OHP (-12.7%) was observed following DS. Similar changes were seen post-DS to plasma from non-anticoagulated patients. Also in this group, pre- and post-DS thrombin generation parameters showed high correlation, with the strongest observed for ETP (R²  = 0.94). There was a strong correlation for OHP parameters, with the closest seen with OCP (R²  = 0.96) and OHP (R²  = 0.95).

CONCLUSION

DS causes some changes to the ETP and OHP assay, however, strong correlations were seen pre- and post-DS in all GCA parameters. These findings support the use of DS to facilitate GCA testing in anticoagulated individuals for evaluation of the underlying thrombotic state.

Dissimilarity in coagulation system in adults after Fontan surgery based on thrombin generations

OBJECTIVES

The Fontan procedure is the treatment of choice in congenital cardiac malformations defined as the single ventricle. Fontan patients are at high risk of thromboembolism, but the exact mechanism of this is poorly understood. The aim of this study was to evaluate an involvement of thrombin generations and microparticles (MPs) in prothrombotic state in adults with Fontan circulation.

METHODS

This study included hospitalized patients after Fontan procedure and healthy volunteers. We assessed laboratory tests including thrombin generation by calibrated automated thrombography in three variants [platelet-poor plasma (impact of coagulation factors), platelet-rich plasma (PRP) (influence of platelets) and related with MPs]. The technique allows for a comprehensive evaluation of the coagulation system.

RESULTS

The study groups consisted of 81 adult Fontan patients [41 females (50.6%); median age 22 interquartile range [20-27] years] and 54 control subjects. In patients with Fontan circulation, higher values of endogenous thrombin potential and peak values were observed for both platelet-poor plasma (+17% and +33%) and MPs (+29% and 41%) compared to controls (all P < 0.05). Moreover, in the Fontan group, we found a 64.9% shorter lag time and a 70.4% time to peak for MP variant (both P < 0.001). Contrarily, analysis in the PRP showed 17.1% of reduced endogenous thrombin potential in Fontan. Furthermore, there were no differences in thrombin synthesis in PRP in Fontan patients receiving aspirin or those with thrombocytopaenia (all P > 0.05).

CONCLUSIONS

This study for the first time showed that thrombin generation associated with MPs may be an important contributor to the prothrombotic state in the Fontan population.

Assessing the individual roles of FII, FV, and FX activity in the thrombin generation process

Thrombin generation (TG) is known as a physiological approach to assess the hemostatic function. Although it correlates well with thrombosis and bleeding, in the current setup it is not sensitive to the effects of fluctuations in single coagulation factors. We optimized the calibrated automated thrombinography (CAT) method to quantify FII, FV and FX activity within the coagulation system. The CAT assay was fine-tuned for the assessment of FII, FV and FX by diluting the samples in FII-, FV-, or FX-deficient plasma, respectively, and measuring TG. Plasma FII levels correlated linearly with the ETP up to a plasma concentration of 100% FII. FV and FX levels correlated linearly with the peak height up to a plasma level of 2.5% FV and 10% FX, respectively. Sensitized CAT protocols were designed by adding a fixed volume of a pre-diluted patient sample to FII, FV, and FX deficient plasma in TG experiments. This approach makes the TG measurement dependent on the activity of the respective coagulation factor. The ETP or peak height were quantified as readouts for the coagulation factor activity. The intra- and inter-assay variation coefficients varied from 5.0 to 8.6%, and from 3.5 to 5.9%, respectively. Reference values were determined in 120 healthy subjects and the assays were clinically validated in 60 patients undergoing coronary artery bypass grafting (CABG). The sensitized CAT assays revealed that the contribution of FII, FV, and FX to the TG process was reduced after CABG surgery, leading to reduced prothrombin conversion and subsequently, lower TG.

Effect of Pulsatility on the Transport of Thrombin in an Idealized Cerebral Aneurysm Geometry

Computational models of cerebral aneurysm thrombosis are designed for use in research and clinical applications. A steady flow assumption is applied in many of these models. To explore the accuracy of this assumption a pulsatile-flow thrombin-transport computational fluid dynamics (CFD) model, which uses a symmetrical idealized aneurysm geometry, was developed. First, a steady-flow computational model was developed and validated using data from an in vitro experiment, based on particle image velocimetry (PIV). The experimental data revealed an asymmetric flow pattern in the aneurysm. The validated computational model was subsequently altered to incorporate pulsatility, by applying a data-derived flow function at the inlet boundary. For both the steady and pulsatile computational models, a scalar function simulating thrombin generation was applied at the aneurysm wall. To determine the influence of pulsatility on thrombin transport, the outputs of the steady model were compared to the outputs of the pulsatile model. The comparison revealed that in the pulsatile case, an average of 10.2% less thrombin accumulates within the aneurysm than the steady case for any given time, due to periodic losses of a significant amount of thrombin-concentrated blood from the aneurysm into the parent vessel’s bloodstream. These findings demonstrate that pulsatility may change clotting outcomes in cerebral aneurysms.

Thrombin generation by calibrated automated thrombography in goat plasma: Optimization of an assay

The goat model of atrial fibrillation (AF) allows investigation of the effect of AF on coagulation. However, assays for goat plasma are not available from commercial sources. Calibrated automated thrombography (CAT) provides a global view of the coagulation profile by assessing in vitro thrombin generation (TG). We describe the customization of the CAT assay in goat platelet-poor plasma (PPP) and in factor Xa (FXa)-inhibitor-anticoagulated PPP. TG was initiated in the presence of phospholipids and either (a) PPP reagent, reagent low, or reagent high; (b) goat brain protein extraction (GBP); or (c) Russell's viper venom-factor X activator (RVV-X). Contact activation was assessed by adding corn trypsin inhibitor. Different concentrations of prothrombin complex concentrate (PCC) were used to determine the sensitivity of both the GBP and RVV-X method. To obtain FXa-inhibitor anticoagulated plasma, rivaroxaban was added to plasma. TG settings with human reagents were not suitable for goat plasma. TG triggered with GBP increased peak height and ETP values. Similarly, the RVV-X method produced comparable TG curves and was more sensitive to PCC titration. Finally, both methods were able to detect the decrease in clotting potential induced by FXa inhibition. This is the first study that reports the customization of the CAT assay for goats. The GBP and RVV-X methods were comparable in triggering TG in goat plasma. The RVV-X method seemed to better discriminate changes in TG curves due to increases in clotting potential as well as to FXa inhibition by rivaroxaban in goat plasma.

Influence of direct oral anticoagulants on thrombin generation on Ceveron TGA

INTRODUCTION

Monitoring of direct oral anticoagulants (DOACs) with calibrated anti-Xa assay is limited by the high intra- and interindividual variations of the test results. Thrombin generation (TG) is a global hemostatic assay that reflects the patient´s individual coagulation status. The aim of this study was to investigate the influence of DOACs on TG measured with a fully automated assay system.

METHODS

All consecutive patients under apixaban and rivaroxaban coming to the outpatient coagulation center MVZ Limbach, Magdeburg, Germany between October 2017 and April 2020 were included. DOAC plasma levels were correlated with TG assessed using the fully automated Ceveron TG analyzer.

RESULTS

A total of 703 rivaroxaban and 252 apixaban containing plasma samples were included. There was a significant correlation between DOAC plasma levels and all TG parameters except for lag time regarding apixaban. Time to peak and peak thrombin followed an exponential regression curve, while this was linear for the endogenous thrombin potential (ETP). Apixaban showed a lower correlation coefficient for all TG parameters compared with rivaroxaban, and thrombin generation was less influenced by apixaban than rivaroxaban at plasma levels >100 ng/ml. The sensitivity and negative predictive value of normal TG parameters for the prediction of DOAC plasma levels <30 ng/ml was >85%.

CONCLUSION

The present data show a moderate predominantly nonlinear correlation between TG parameters and plasma levels of apixaban and rivaroxaban. Rivaroxaban has a stronger effect on TG than apixaban.

The Impact of Dabigatran and Rivaroxaban on Variation of Platelet Activation Biomarkers and DRT Following Percutaneous Left Atrial Appendage Closure

Background: The current post-procedure antithrombotic recommendation for left atrial appendage closure (LAAC) remains empiric. This study was designed to compare variations in platelet activation biomarkers and device-related thrombosis (DRT) under different antithrombotic regimens following LAAC. Methods: This study enrolled 105 consecutive patients with atrial fibrillation who underwent LAAC successfully and received post-procedure anticoagulation with either dabigatran (N = 33) or rivaroxaban (N = 72). After 3 months of anticoagulation treatment, thromboelastogram was used to evaluate thrombin receptor-activating peptide (TRAP)-induced platelet aggregation (PA). Measurements of platelet activation biomarkers, including thrombin-antithrombin complex (TAT), P-selectin, von Willebrand disease (vWF), and CD40L, were performed immediately before the LAAC procedure and after 3 months of post-procedure anticoagulation. Repeated transesophageal echocardiography was performed to evaluate DRT during follow-ups. Results: Three (4.2%) patients in the rivaroxaban and 4 (12.1%) patients in the dabigatran group experienced DRT events (odds ratio (OR) = 0.315, 95% confidence interval (95%CI): 0.066-1.489, p = 0.129) during follow-ups. The TRAP-induced PA was statistically significantly higher in the dabigatran group (62.9% vs 59.7%, p = 0.028*). Statistically significant increases in plasma concentration of TAT, P-selectin, and vWF were observed after 3 months of exposure to dabigatran when compared with rivaroxaban. An increased expression of platelet activation biomarkers was observed in DRT subjects compared with non-DRT subjects in terms of P-selectin and vWF (65.28 ± 13.93 ng/L vs 32.14 ± 12.11 ng/L, p = 0.037; 501.92 ± 106.48 U/L vs 280.98 ± 54.10 U/L, p = 0.045; respectively). Multivariate regression analysis indicated that the use of dabigatran might be an independent predictor of DRT (p = 0.022; OR = 4.366, 95%CI: 0.434-10.839). Furthermore, the CHA2DS2-VASc score (OR = 2.076, p = 0.016) and CD40L levels (OR = 1.015, p = 0.021) were independent predictors of increased D-dimer levels. Conclusions: Post-LAAC anticoagulation with dabigatran may increase the risk of DRT by enhancing platelet reactivity. In light of this potential increased risk in DRT, the authors recommend against using dabigatran for post-procedural anticoagulation in patients who have undergone LAAC.

Safety and efficacy of direct oral anticoagulants under long-term immunosuppressive therapy after liver, kidney and pancreas transplantation

The safety of direct oral anticoagulants (DOACs) in patients after solid organ transplantation (SOT) is not well defined. This study aimed at describing the safety and efficacy of DOACs in patients after SOT. Patients after kidney and/or liver transplantation under maintenance immunosuppression treated with rivaroxaban (n = 26), apixaban (n = 20) and edoxaban (n = 1) were included. Clinical data were collected retrospectively and using a questionnaire. DOAC plasma levels and thrombin generation (TG) were measured in patients after SOT and compared with nontransplanted controls receiving DOACs. DOACs were administered for 84.6 patient-years. Mean immunosuppressive trough levels after DOAC initiation increased from baseline by 18.8 ± 29.6% compared to 3.0 ± 16.5% in matched controls (P = 0.004), without significant differences in dose adjustments. No transplant rejection or significant change in liver or renal function was observed. There was one major bleeding after the observation period but no thromboembolic complication. DOAC plasma levels reached the expected range in all patients. The intrinsic hemostatic activity in transplanted patients was higher compared to nontransplant controls. Treatment with DOACs after SOT is safe and effective. Immunosuppressive trough levels should be monitored after DOAC initiation, particularly in the early phase after SOT. These data should be confirmed in a prospective study.

Individualised Risk Assessments for Recurrent Venous Thromboembolism: New Frontiers in the Era of Direct Oral Anticoagulants

Venous thromboembolism (VTE) is a leading cause of morbidity and mortality and is associated with high recurrence rates. The introduction of direct oral anticoagulants (DOACs) in the 2010s has changed the landscape of VTE management. DOACs have become the preferred anticoagulant therapy for their ease of use, predictable pharmacokinetics, and improved safety profile. Increasingly, guidelines have recommended long term anticoagulation for some indications such as following first unprovoked major VTE, although an objective individualised risk assessment for VTE recurrence remains elusive. The balance of preventing VTE recurrence needs to be weighed against the not insignificant bleeding risk, which is cumulative with prolonged use. Hence, there is a need for an individualised, targeted approach for assessing the risk of VTE recurrence, especially in those patients in whom the balance between benefit and risk of long-term anticoagulation is not clear. Clinical factors alone do not provide the level of discrimination required on an individual level. Laboratory data from global coagulation assays and biomarkers may provide enhanced risk assessment ability and are an active area of research. A review of the prediction models and biomarkers for assessing VTE recurrence risk is provided, with an emphasis on contemporary developments in the era of DOACs and global coagulation assays.

Effects of rivaroxaban and dabigatran on global hemostasis in patients with atrial fibrillation

: The study was aimed to evaluate the effects of two standard doses of rivaroxaban and dabigatran on global hemostatic assays in patients with atrial fibrillation. The study included 52 patients treated with rivaroxaban (15/20 mg), 50 on dabigatran (110/150 mg) and 20 healthy individuals. Platelet-poor plasma was used for determination of three global hemostatic assays, namely endogenous thrombin potential (ETP), calibrated automated thrombogram (CAT) and overall hemostasis potential (OHP). Rivaroxaban and dabigatran reduced ETP (P < 0.01) although OHP (P < 0.05) was diminished only by dabigatran. Strong correlations were noticed between ETP parameters and the plasma concentrations of rivaroxaban (ETP, r = -0.51; c-max, r = -0.85; t-lag, r = 0.83; t-max, r = 0.66) as well as with plasma concentration of dabigatran (ETP, r = -0.75; c-max, r = -0.74; t-lag, r = 0.73; t-max, r = 0.52). Analysis of dabigatran concentrations under 50 ng/ml showed that ETP parameter has area under the concentration-time curve-receiver operating characteristic value of 0.879 (95% confidence interval 0.776-0.980). Dabigatran treatment paradoxically increased area under the concentration-time curve and peak values although rivaroxaban decreased peak values (P < 0.01). However, significant correlation between CAT parameters and plasma concentration of both direct oral anticoagulants was not observed. We confirmed that the CAT assay is inappropriate for estimation of dabigatran effects and is not fully sensitive as regards rivaroxaban. The ETP assay can potentially be the appropriate method for estimation of global hemostatic capacity as regards both direct oral anticoagulants. The role of OHP needs to be confirmed in additional studies. ETP parameter of chromogenic assay has promising potential in exclusion of high plasma concentrations of dabigatran.

Study of thrombin generation with St Genesia to evaluate xaban pharmacodynamics: Analytical performances over 18 months

INTRODUCTION

ST Genesia is a new automated system enabling quantitative standardized evaluation of thrombin generation (TG), for example, in patients receiving anti-Xa direct inhibitors (xabans). Data on its analytical performances are scarce.

METHODS

Over an 18-month period, repeatability, reproducibility, and accuracy were assessed using STG-ThromboScreen (without or with thrombomodulin) or STG-DrugScreen reagents (corresponding to intermediate/high tissue-factor concentration, respectively), and controls. Furthermore, reproducibility was assessed using commercialized lyophilized and frozen normal pooled plasmas. Rivaroxaban and apixaban impacts on TG parameters were assessed using spiking experiments. Finally, a comparison with the Calibrated Automated Thrombogram method (CAT) (PPP reagent) was performed using plasma from healthy volunteers enrolled in the DRIVING-studyNCT01627665) before and after rivaroxaban intake.

RESULTS

For all dedicated quality control (QC) levels, inter-series coefficients of variations (CV) were <7% for temporal TG parameters, peak height (PH), and endogenous thrombin potential (ETP), whether results were normalized with a dedicated reference plasma STG-RefPlasma or not. Noteworthy, STG-RefPlasma used for normalization displayed substantially high PH and ETP. Mean biases between the observed and manufacturer's assigned QC values were mostly <7%. Both rivaroxaban/apixaban plasma concentrations were significantly associated with TG parameters. Finally, Bland-Altman plots showed a good agreement between ST Genesia-STG-ThromboScreen and CAT method within the explored range of values, although biases could be observed (PH: 16.4 ± 13.2%, ETP: 17.8 ± 11.9%).

CONCLUSION

ST Genesia^® enables the reliable measurement of TG parameters in both in vitro and ex vivo xaban plasma samples using either STG-ThromboScreen or STG-DrugScreen according to xaban concentrations. The use of reference plasma, despite not completely reflecting a normal pooled plasma behavior, likely improves standardization and inter-laboratory comparisons.

Delayed Thrombin Generation Is Associated with Minor Bleedings in Venous Thromboembolism Patients on Rivaroxaban: Usefulness of Calibrated Automated Thrombography

Bleeding is the most feared and difficult to predict adverse event of anticoagulation. We sought to investigate whether calibrated automated thrombography (CAT) parameters are associated with minor bleeding (MB) in anticoagulated patients following venous thromboembolism (VTE). Enrolled were 132 patients on rivaroxaban, 145 on vitamin K antagonists (VKA) and 31 controls who stopped anticoagulation. Prior to the next dose of the anticoagulant, we measured CAT parameters, along with rivaroxaban concentration and INR. During a median follow-up of 10 months, we recorded minor and major bleedings. On rivaroxaban, 27 (20.5%) patients with MB had longer time to start thrombin generation, lower peak thrombin generation and lower endogenous thrombin potential compared with subjects without MB (all p < 0.001). All CAT parameters, except for peak thrombin generation (p = 0.049), were similar in VKA patients with (n = 25, 17.2%) vs. without MBs. By logistic regression, time to start thrombin generation (p = 0.007) and unprovoked VTE (p = 0.041) independently predicted MBs on rivaroxaban. Major bleedings were more frequent in patients with MBs (17.3% vs. 1.8%, p < 0.001). Abnormal CAT parameters characterize VTE patients prone to MBs on rivaroxaban, but not on VKA. Time to start thrombin generation measured about 24 h since the last rivaroxaban dose might help predict MBs.

Inhibition of thrombin generation 12 hours after intake of direct oral anticoagulants

BACKGROUND

The residual antithrombotic activity 12 hours after intake of direct oral anticoagulants (DOACs) is of clinical relevance in the setting of bleeding or urgent surgery.

OBJECTIVE

To evaluate the effects of DOACs on thrombin generation 12 hours after DOAC intake in comparison to baseline and a healthy control group.

METHODS

Eighty patients were recruited, 20 patients for each approved DOAC: apixaban, edoxaban, rivaroxaban, and dabigatran. The patients were either to be put on anticoagulation for the first time or had stopped taking oral anticoagulation for at least 48 hours. Blood plasma was sampled before (baseline) and 12 hours after starting DOAC for quantification of drug levels and thrombin generation assayed using an automated system (ST Genesia). Sixty-one blood donors served as control group.

RESULTS

The factor Xa inhibitors significantly increased lag time (137%-219%) and reduced thrombin peak (47%-76%) and velocity index (17%-44%) after 12 hours compared to baseline. Dabigatran showed prolongation of lag time to 133% and time to peak to 119%. All patients had residual antithrombotic activity, with reduced thrombin generation parameters 12 hours after DOAC intake compared to baseline and to the healthy control group. This effect remained significant in patients with low residual DOAC plasma levels <50 ng/mL.

CONCLUSION

Thrombin generation remains reduced 12 hours after DOAC intake. While thrombin peak is particularly modified by factor Xa inhibitors, all DOACs prolong the lag time and time to thrombin peak. In the setting of bleeding or urgent surgery, the automated thrombin generation assay may assist in decision making and antidote administration.

Rivaroxaban Effects Illustrate the Underestimated Importance of Activated Platelets in Thrombin Generation Assessed by Calibrated Automated Thrombography

Background: The direct oral anticoagulant rivaroxaban inhibiting specifically activated factor X (FXa) causes delayed thrombin generation (TG) as measured by calibrated automated thrombography (CAT). The implications of these changes for assessing bleeding or residual prothrombotic risks of patients are unclear in the absence of a better understanding of the underlying mechanism. Methods: We compared platelet rich plasma (PRP) without or with prior collagen-induced platelet aggregation (agPRP) in the CAT assay to better characterize TG in the presence of rivaroxaban. Results: In the presence of rivaroxaban, TG curves in agPRP showed a distinct profile with a rapidly ascending phase followed with a protracted phase. Inhibition of tissue factor pathway inhibitor amplified the first phase of the curve which was also modulated by procoagulant phospholipids. Inhibition of FXIIa-dependent FXI activation revealed that aggregated platelets influenced the first phase by a combination of extrinsic and intrinsic coagulation pathway initiations. Thrombin-dependent amplification of TG (even prior collagen activation) was responsible for the second phase of the TG curve. Conclusions: AgPRP fully includes platelet ability to support TG and reveal distinct TG phases in the presence of direct FXa inhibitors highlighting its potential use in an anticoagulated setting.

Assessment of the analytical performances and sample stability on ST Genesia system using the STG-DrugScreen application

BACKGROUND

Thrombin generation testing has been used to provide information on the coagulation phenotype of patients. The most used technique is the calibrated automated thrombogram (CAT) but it suffers from a lack of standardization, preventing its implementation in routine. The ST Genesia is a new analyzer designed to assess thrombin generation based on the same principle as the CAT. Unlike the CAT system, the ST Genesia is a benchtop, fully automated analyzer, able to perform the analyses individually and not by batch, with strict control of variables such as temperature and volumes, ensuring, theoretically, maximal reproducibility.

OBJECTIVES

This study aimed at assessing the performance of the STG-DrugScreen application on the ST Genesia analyzer. We also aimed at exploring stability of plasma samples after freezing and defining a reference normal range.

RESULTS

Results demonstrated the excellent interexperiment precision of the ST Genesia and confirmed that the use of a reference plasma helps reducing the inter-experiments variability. Stability revealed that plasma samples are stable for at least 11 months at -70°C or lower, except for those containing low molecular weight heparins which have to be tested within 6 months. Freezing had no effect on the majority of thrombin generation parameters except on time to peak.

CONCLUSIONS

Our results suggest an easy implementation of thrombin generation with the use of ST Genesia in the routine laboratory. This will facilitate the design of multicentric studies and enable the establishment of reliable and evidence-based thresholds, which may improve the management of patients treated with anticoagulants.

A review of global coagulation assays - Is there a role in thrombosis risk prediction?

Normal haemostasis requires maintenance of a careful equilibrium between the necessity to clot when bleeding and the retention of fluid phase at all other times. Disruption of this equilibrium can result in catastrophic outcomes, e.g. acute myocardial infarction and pulmonary embolism. However, despite the significant therapeutic advances in cardiovascular medicine over recent years, our ability to provide an accurate cardiovascular risk assessment remains an unmet need. Routine coagulation testing is not a useful reflection of haemostasis and cannot be reliably used to predict bleeding and thrombosis risks. Global coagulation assays such as viscoelastic testing, thrombin and fibrin generation have been proposed as better measures of the haemostatic function. These assays, particularly viscoelastic testing, have been increasingly used to assess bleeding risks and guide blood product replacement in trauma and massive transfusion settings. However, the role of these assays in thrombosis is less well-defined but given the complexities of the coagulation system, these global coagulation assays when used in combination may provide a better assessment of cardiovascular and thrombosis risk at an individual level. Hence, we explore the role of some of the currently available global coagulation assays - the viscoelastic, thrombin generation and fibrin generation tests - and provide a review of the literature of the current evidence for these assays specifically in the field of venous thromboembolism and cardiovascular diseases.

Improving Therapeutic Decisions: Pharmacodynamic Monitoring as an Integral Part of Therapeutic Drug Monitoring

Although the monitoring of drug therapies based on the determination of drug concentrations in biological materials is certainly an important instrument for individualized dosing and dose adjustment with a broad variety of pharmaceuticals, its role is limited by the fact that it does not reflect pharmacodynamic (PD) and toxicodynamic interactions such as those caused by individual and environment-related factors. However, these interactions are important for both the efficacy and the safety of the drug therapy. Therefore, during recent years, there is an increased interest in personalized drug therapy as reflected by the development and clinical implementation of molecular "biomarkers" that are direct or surrogate markers of pharmacological effects [PD therapeutic drug monitoring (TDM)]. Moreover, this process is driven by new developments in instrumentation, such as mass spectrometry and array technologies, and in computational biology/pharmacology, databases, and bioinformatics. This Focus Issue of the journal focuses on current achievements in and status of PD TDM with different classes of drugs. The contributions to the present issue of Therapeutic Drug Monitoring provide a critical analysis of current practices of TDM with their limitations, introduce newer promising biomarkers in the field of PD TDM, discuss the challenges faced to date in translating preclinical tools into clinical settings, and point out recent advances in the establishment of modeling approaches that apply to pharmacokinetics (PK)/PD as well as pharmacogenetic information.

Laboratory Assessment of the Anticoagulant Activity of Apixaban in Patients With Nonvalvular Atrial Fibrillation

Our aim is to determine the most appropriate laboratory tests, besides anti-factor Xa (anti-FXa) chromogenic assays, to estimate the degree of anticoagulation with apixaban and compare it with that of rivaroxaban in real-world patients. Twenty patients with nonvalvular atrial fibrillation treated with apixaban 5 mg twice daily and 20 patients on rivaroxaban 20 mg once daily were studied. Conventional coagulation tests, thrombin generation assay (TGA), and thromboelastometry (nonactivated TEM [NATEM] assay) were performed in the 40 patients and 20 controls. The anti-FXa chromogenic assays were used to measure apixaban and rivaroxaban plasma levels. The NATEM measurements showed no significant difference between the 2 groups of patients. Concerning TGA, endogenous thrombin potential (ETP) was significantly decreased in patients on rivaroxaban as compared to those treated with apixaban (P < .003). A statistically significant, strong inverse correlation between apixaban plasma concentrations and ETP (P < .001) was observed. Apixaban significantly reduces ETP compared to controls, but to a lesser extent than rivaroxaban. Thrombin generation assay might provide additional information on apixaban exposure, which is required in order to individualize treatment especially for patients with a high bleeding risk. Our findings have to be further investigated in studies with larger sample sizes, in the entire range of apixaban exposure, with other direct oral anticoagulants, and in relation to clinical outcomes.