Thrombin generation testing in routine clinical practice: are we there yet?

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.

Effect of prothrombin Belgrade mutation, causing antithrombin resistance, on fibrin clot properties

INTRODUCTION

Prothrombin Belgrade mutation is the result of the c.1787G>A substitution in the prothrombin gene. It is located in the antithrombin and sodium binding site and leads to impaired inactivation of thrombin by antithrombin, resulting in antithrombin resistance and thrombotic disorders. However, it negatively affects sodium binding and may have hypocoagulant effects. Considering that prothrombin Belgrade mutation mechanism is still not fully elucidated and that sodium binding is important for thrombin affinity towards fibrinogen, our aim was to determine whether this mutation affects fibrin clot formation and lysis.

METHODS

Using HEK293T cell line, recombinant wild type and mutated prothrombin were generated by transient transfection. Samples that correspond to plasma of a non-carrier, heterozygous and homozygous carriers were reconstituted using prothrombin deficient plasma and recombinant proteins. Reconstituted samples were used in OHP assay (Overall Hemostasis Potential) to determine kinetic profiles of coagulation and fibrinolysis. Clot turbidity assay was performed to observe kinetics of clot formation and lysis more closely. Fibrin clots formed in reconstituted plasma samples were analyzed by confocal microscopy to determine density of fibrin network. Fibrin clots were additionally observed using electron microscopy to determine thickness of individual fibrin fibers.

RESULTS

No significant difference found in OHP, OCP, OFP, and fibrin network density between wild type, heterozygous, and homozygous carrier reconstituted plasma samples. There were significant differences between samples for slope and slope time parameters in kinetic profiles and fibrin fiber thickness.

CONCLUSIONS

Results indicate that prothrombin Belgrade mutation has no significant impact on fibrinolysis, however it may affect kinetics of clot formation and its architecture.

Comprehensive functional characterization of a novel ANO6 variant in a new patient with Scott syndrome

BACKGROUND

Scott syndrome is a mild platelet-type bleeding disorder, first described in 1979, with only 3 unrelated families identified through defective phosphatidylserine (PS) exposure and confirmed by sequencing. The syndrome is distinguished by impaired surface exposure of procoagulant PS on platelets after stimulation. To date, platelet function and thrombin generation in this condition have not been extensively characterized.

OBJECTIVES

Genetic and functional studies were undertaken in a consanguineous family with a history of excessive bleeding of unknown cause.

METHODS

A targeted gene panel of known bleeding and platelet genes was used to identify possible genetic variants. Platelet phenotyping, flow adhesion, flow cytometry, whole blood and platelet-rich plasma thrombin generation, and specialized extracellular vesicle measurements were performed.

RESULTS

We detected a novel homozygous frameshift variant, c.1943del (p.Arg648Hisfs∗23), in ANO6 encoding Anoctamin 6, in a patient with a bleeding history but interestingly with normal ANO6 expression. Phenotyping of the patient's platelets confirmed the absence of PS expression and procoagulant activity but also revealed other defects including reduced platelet δ granules, reduced ristocetin-mediated aggregation and secretion, and reduced P-selectin expression after stimulation. PS was absent on spread platelets, and thrombi formed over collagen at 1500/s. Reduced thrombin generation was observed in platelet-rich plasma and confirmed in whole blood using a new thrombin generation assay.

CONCLUSION

We present a comprehensive report of a patient with Scott syndrome with a novel frameshift variant in AN06, which is associated with no platelet PS exposure and markedly reduced thrombin generation in whole blood, explaining the significant bleeding phenotype observed.

Clinical Relevance of Preclinical and Clinical Studies of Four-Factor Prothrombin Complex Concentrate for Treatment of Bleeding Related to Direct Oral Anticoagulants

Direct oral anticoagulants (DOACs) are widely used for the prevention and treatment of venous thromboembolism and stroke. When emergency reversal of DOAC-related anticoagulation is required, specific DOAC reversal agents are recommended, including idarucizumab for dabigatran reversal and andexanet alfa for apixaban and rivaroxaban reversal. However, specific reversal agents are not always available, andexanet alfa has not been approved for urgent surgery, and clinicians need to know the patient's anticoagulant medication before administering these treatments. Four-factor prothrombin complex concentrates (4F-PCCs) are recognized as nonspecific, alternative hemostatic agents for treatment of DOAC-related bleeding. Evidence from preclinical and clinical studies shows that they may reduce the anticoagulant effects of DOACs and may help control DOAC-related bleeding. However, randomized controlled trials are lacking, and most data are from retrospective or single-arm prospective studies in bleeding associated with activated factor X inhibitors. There are no clinical data showing the efficacy of 4F-PCC for the treatment of bleeding in dabigatran-treated patients. This review focuses on the current evidence of 4F-PCC use in controlling bleeding associated with DOACs and provides an expert opinion on the relevance of these data for clinical practice. The current treatment landscape, unmet needs, and future directions are also discussed.

The Role of Biomarkers, Metabolomics, and COVID-19 in Venous Thromboembolism-A Review of Literature

In recent years, the field of venous thromboembolism has undergone numerous innovations, starting from the recent discoveries on the role of biomarkers, passing through the role of metabolomics in expanding our knowledge on pathogenic mechanisms, which have opened up new therapeutic targets. A variety of studies have contributed to characterizing the metabolic phenotype that occurs in venous thromboembolism, identifying numerous pathways that are altered in this setting. Among these pathways are the metabolism of carnitine, tryptophan, purine, and fatty acids. Furthermore, new evidence has emerged with the recent COVID-19 pandemic. Hypercoagulability phenomena induced by this viral infection appear to be related to altered von Willebrand factor activity, alteration of the renin-angiotensin-aldosterone system, and dysregulation of both innate and adaptive immunity. This is the first literature review that brings together the most recent evidence regarding biomarkers, metabolomics, and COVID-19 in the field of venous thromboembolism, while also mentioning current therapeutic protocols.

Use of thrombomodulin-modified thrombin generation in uncomplicated pregnancy: the normal range and prothrombotic phenotype

Pregnancy is a hypercoagulable state associated with an increased risk of venous thrombosis. Thrombomodulin(TM)-modified thrombin generation is a promising laboratory method to detect the thrombotic tendency and prothrombotic phenotype. 141 women were enrolled: 30 healthy non-pregnant controls, 85 healthy pregnant women (26 in 1st trimester, 28 in 2nd trimester, 31 in 3rd trimester), and 26 patients with gestational diabetes mellitus (GDM). Thrombin generation was measured using platelet poor plasma (PPP) TM + and PPP TM- reagents. The parameters were endogenous thrombin potential (ETP), Lagtime, Peak Height, time to peak and ETP ratio(ETP(TM+)/ETP(TM-)). Protein S-depleted plasma samples with different activity were prepared and measured. Pregnancy was associated with a significant decrease of ETP in the presence of TM, compared with that found in the absence of TM. This was observed in all trimesters (1st trimester 1185.67 ± 284.95 nM*min vs.1510.39 ± 281.90 nM*min, p < .001; 2nd trimester 1458.96 ± 349.65 nM*min vs. 1929.10 ± 316.98 nM*min, p < .001; 3rd trimester 1391.60 ± 317.05 nM*min vs. 1854.88 ± 327.60 nM*min, p < .001). The ETP ratio was also markedly increased in all trimesters (0.78 ± 0.10, 0.76 ± 0.11 and 0.74 ± 0.12) compared with that of non-pregnant controls (0.51 ± 0.17, p < .001). The results of ETP ratio in protein S-depleted plasmas were 0.986, 0.943 and 0.880 with 0%, 16% and 40% of protein S activity, which indirect represented the thrombotic phenotype of PS deficiency in pregnancy. TM-modified thrombin generation serves as a useful test for hypercoagulation in pregnant women. The ETP ratio and the reference range of ETP in the presence of TM could provide the basis to predict the risk of thrombotic complications during pregnancy.

Haemostasis and Inflammatory Parameters as Potential Diagnostic Biomarkers for VTE in Trauma-Immobilized Patients

Venous thromboembolism (VTE), which encompasses deep venous thrombosis (DVT) and pulmonary embolism (PE), is a major public health concern due to its high incidences of morbidity and mortality. Patients who have experienced trauma with prolonged immobilization are at an increased risk of developing VTE. Plasma D-dimer levels have been known to be elevated in trauma patients, and they were closely correlated with the number of fractures. In other words, plasma D-dimer levels cannot be used as the only indicator of VTE in trauma cases. Given the limitations, further study is needed to explore other potential biomarkers for diagnosing VTE. To date, various established and novel VTE biomarkers have been studied in terms of their potential for predicting VTE, diagnostic performance, and improving clinical therapy for VTE. Therefore, this review aims to provide information regarding classic and essential haemostasis (including prothrombin time (PT), activated partial thromboplastin time (aPTT), D-dimer, fibrinogen, thrombin generation, protein C, protein S, antithrombin, tissue factor pathway inhibitor, and platelet count) and inflammatory biomarkers (C-reactive protein, erythrocyte sedimentation rate, and soluble P-selectin) as potential diagnostic biomarkers that can predict the risk of VTE development among trauma patients with prolonged immobilization. Thus, further advancement in risk stratification using these biomarkers would allow for a better diagnosis of patients with VTE, especially in areas with limited resources.

Thrombin generation and implications for hemophilia therapies: A narrative review

Thrombin plays an essential role in achieving and maintaining effective hemostasis and stable clot formation. In people with hemophilia, deficiency of procoagulant factor (F)VIII or FIX results in insufficient thrombin generation, leading to reduced clot stability and various bleeding manifestations. A correlation has been found between the bleeding phenotype of people with hemophilia and the extent of thrombin generation, with individuals with increased thrombin generation being protected from bleeding and those with lower thrombin generation having increased bleeding tendency. The amount, location, and timing of thrombin generation have been found to affect the formation and stability of the resulting clot. The goal of all therapies for hemophilia is to enhance the generation of thrombin with the aim of restoring effective hemostasis and preventing or controlling bleeding; current treatment approaches rely on either replacing or mimicking the missing procoagulant (ie, FVIII or FIX) or rebalancing hemostasis through lowering natural anticoagulants, such as antithrombin. Global coagulation assays, such as the thrombin generation assay, may help guide the overall management of hemostasis by measuring and monitoring the hemostatic potential of patients and, thus, assessing the efficacy of treatment in people with hemophilia. Nevertheless, standardization of the thrombin generation assay is needed before it can be adopted in routine clinical practice.

Rational hemostatic management in cirrhosis: from old paradigms to new clinical challenges

INTRODUCTION

Patients with cirrhosis are at risk of both thrombotic and hemorrhagic events. Traditional hemostatic tests are inadequate to assess the complex and fragile balance of hemostasis in this setting, especially in advanced stages of disease such as decompensated cirrhosis or acute on chronic liver failure (ACLF). Furthermore, the indiscriminate use of pro-hemostatic agents for prophylaxis and treatment of bleeding episodes is still debated and often contraindicated. Alongside, splanchnic, and peripheral thrombotic events are frequent in this population and require management that involves a careful balance between risks and benefits of antithrombotic therapy.

AREAS COVERED

This review aims to address the state of the art on the clinical management of the hemostatic balance of cirrhosis in terms of established knowledge and future challenges.

EXPERT OPINION

The old paradigm of cirrhosis as a naturally anticoagulated condition has been challenged by more sophisticated global tests of hemostasis. Integrating this information in the clinical decision-making is still challenging for physicians and experts in hemostasis.

Nanozyme and Stimulated Fluorescent Cu-Based Metal-Organic Frameworks (Cu-MOFs) Functionalized with Engineered Aptamers as a Molecular Recognition Element for Thrombin Detection in the Plasma of COVID-19 Patients

An essential tool in the management and control of the COVID-19 pandemic is the development of a fast, selective, sensitive, and inexpensive COVID-19 biomarkers detection method. Herein, an ultrasensitive and label-free biosensing strategy was described for the colorimetric and fluorimetric detection of thrombin. A dual-mode aptasensing method based on integrating engineered ssDNA with a stimulated fluorescent enzyme-mimetic copper-based metal-organic framework (Cu-MOF) as a molecular recognition element for thrombin was investigated. Cu-MOFs displayed stimulated fluorescence and enzyme-mimetic peroxidase activities that oxidize the chromogenic colorless substance TMB to blue-colored oxTMB. The thrombin-based aptamer (ssDNA) can be immobilized on the Cu-MOF surface to form a functionalized composite, ssDNA/MOF, and quench the stimulated fluorescence emission and the enzymatic activity of the Cu-MOF. Later, addition of thrombin recovers the fluorescence and enzymatic activity of the MOF. Thus, a turn-on colorimetry/fluorimetry aptasensing probe was designed for the detection of thrombin. Based on colorimetric assay, 350 pM was recorded as the lower limit of detection (LOD), while based on the fluorescence mode, 110 fM was recorded as the LOD (when S/N = 3). The label-free aptasensing probe was used successfully for the detection of thrombin in COVID-19 patients with satisfactory recoveries, 95-98%. Since the detection time of our aptasensor is relatively rapid (45 min) and due to the low-cost precursors and easy-to-operate characteristics, we believe that it has great potential to be used in point-of-care testing (POCT).

Thrombin generation as a predictor of outcomes in patients with non-traumatic intracerebral hemorrhage

Background

Non-traumatic intracerebral hemorrhage (ICH) accounts for 10–15% of all strokes and leads to a higher rate of mortality as compared to ischemic strokes. We aimed to find out whether the thrombin generation assay (TGA) could predict outcomes in patients with ICH.

Patients and methods

In this prospective, observational study, 87 consecutive patients with ICH and 164 healthy controls were included. Computed tomography (CT), detailed clinical investigation, and laboratory investigations were performed from patients on admission. TGA was performed using stored platelet poor plasma obtained on admission. Lag time, endogen thrombin potential (ETP), peak thrombin, and time to peak parameters were calculated. Short- and long-term outcomes of ICH were defined at 14 days and 3 months post-event according to the NIHSS and the modified Rankin Scale (mRS), respectively.

Results

Peak thrombin was significantly higher in patients as compared to controls (397.2 ± 93.9 vs. 306 ± 85.3 nM, p < 0.0001). Lag time, ETP, and time to peak parameters showed a significant positive correlation with CRP in both groups. In patients with worse long-term functional outcomes, peak thrombin was significantly higher as compared to those with favorable outcomes [mRS 2–6 median: 402.5 (IQR:344.8–473.8) vs. mRS 0–1: 326.4 (294.2–416.1) nM, p = 0.0096]. Based on the statistically optimal threshold of 339.1 nM peak thrombin, the sensitivity and specificity of this parameter to determine mRS 2–6 as an outcome were 80.8 and 64.7%, respectively. In a binary logistic regression model including age, sex, BMI, smoking status, NIHSS on admission, D-dimer, and peak thrombin (>339.1 nM), only NIHSS and the peak thrombin parameters remained in the model as significant, independent predictors of poor outcome. Lag time and time to peak showed a modest, significant negative correlation with intracerebral bleeding volume on admission (r = −0.2603, p = 0.0231 and r = −0.3698, p = 0.0010, respectively). During the follow-up of patients, estimated hemorrhage volumes on day 90 showed significant positive association with the ETP and peak thrombin parameters (r = 0.3838, p = 0.0363 and r = 0.5383, p = 0.0021, respectively).

Conclusion

In patients with ICH, TG was increased as compared to healthy controls, which might be explained by the presence of higher inflammatory parameters in patients. Peak thrombin measured on admission might be a useful tool to predict outcomes in patients with ICH.

Increased BMI and Blood Lipids Are Associated With a Hypercoagulable State in the Moli-sani Cohort

The coagulation system can be assessed by the thrombin generation (TG) assay, and increased TG peak height, endogenous thrombin potential (ETP), and velocity index are associated with an increased risk of thrombosis. Obesity had been reported to increase TG and is associated with dyslipidemia, which also predisposes to atherosclerotic cardiovascular disease (CVD). However, the effect of the blood lipid profile on TG has not been studied extensively. To gain more insight into the associations of TG, body mass index (BMI) and lipid profile, we studied TG in relation to these parameters in a large Italian population cohort, the Moli-sani study (N = 22,546; age ≥ 35 years; 48% men). TG was measured in plasma samples collected at the enrollment of subjects in the Moli-sani study. TG was triggered with 1 or 5 pM tissue factor, and TG parameters lag time, peak, ETP, time-to-peak (TTP) and velocity index (VI). Additionally, thrombomodulin was added to assess the function of the activated protein C system during TG. In both women and men, overweight (BMI 25–30 kg/m²) and obesity (BMI > 30 kg/m²) were significantly associated with higher ETP, peak and VI (all p < 0.001). High total cholesterol, triglycerides and LDL-cholesterol levels were significantly associated with increased ETP and peak (all p < 0.001). Linear regression analysis revealed that the ETP is positively associated with both plasma LDL and HDL cholesterol levels, whereas the velocity index is positively associated with HDL cholesterol. Additionally, ETP, peak and VI were significantly associated with the plasma triglycerides content. In conclusion, our study shows significant associations of high BMI and blood lipid levels with increased TG parameters, and this hypercoagulability may partly explain the increased risk of CVD in individuals with obesity and/or dyslipidemia.

The role of the calibrated automated thrombogram in neonates: describing mechanisms of neonatal haemostasis and evaluating haemostatic drugs

Premature infants are at high risk of haemorrhage and thrombosis. Our understanding of the differences between the neonatal and adult haemostatic system is evolving. There are several limitations to the standard coagulation tests used in clinical practice, and there is currently a lack of evidence to support many of the transfusion practices in neonatal medicine. The evaluation of haemostasis is particularly challenging in neonates due to their limited blood volume. The calibrated automated thrombogram (CAT) is a global coagulation assay, first described in 2002, which evaluates both pro- and anti-coagulant pathways in platelet-rich or platelet-poor plasma. In this review, the current applications and limitations of CAT in the neonatal population are discussed.Conclusion: CAT has successfully elucidated several differences between haemostatic mechanisms in premature and term neonates compared with adults. Moreover, it has been used to evaluate the effect of a number of haemostatic drugs in a pre-clinical model. However, the lack of evidence of CAT as an accurate predictor of neonatal bleeding, blood volume required and the absence of an evidence-based treatment algorithm for abnormal CAT results limit its current application as a bedside clinical tool for the evaluation of sick neonates. What is Known: • The Calibrated automated thrombogram (CAT) is a global coagulation assay which evaluates pro- and anti-coagulant pathways. • CAT provides greater information than standard clotting tests and has been used in adults to evaluate bleeding risk. What is New: • This review summarises the physiological differences in haemostasis between neonates and adults described using CAT. • The haemostatic effect of several drugs has been evaluated in neonatal plasma using CAT.

Thrombin generation measured on ST Genesia, a new platform in the coagulation routine lab: Assessment of analytical and between-subject variation

BACKGROUND

The thrombin generation (TG) assay, which measures global coagulation, has mainly been used as a research tool to investigate thrombotic and bleeding disorders. Recently, Diagnostica Stago launched the ST Genesia, a fully automated system to perform "routine version" of this assay. The objectives of this study were to evaluate the imprecision compared with the previous method, Thrombinoscope CAT, and to establish reference intervals.

METHODS

Thrombin generation was measured in platelet-poor citrated plasma from 20 normal controls (fresh and after freezing at -80°C up to 12-13 weeks) on CAT and ST Genesia in duplicate to estimate the total variation, and within and between variations. The reference intervals were estimated nonparametrically in 30 men, 30 women taking combined oral contraceptives (COCs), and 30 women not taking COCs. These were sampled in both Vacutainer and Monovette tubes (i.e., tubes with a high and minimal contact activation, respectively).

RESULTS

Freezing had minimal effects. Imprecision was comparable between the ST Genesia and CAT, with a strong correlation between the two methods. TG was higher when sampled in Vacutainer than in Monovette. We observed a distinct difference between women taking and not taking COCs, whereas men and women not taking COC were quite similar.

CONCLUSIONS

Thrombin generation on ST Genesia showed an analytical variation similar to that of CAT. The results depended on the type of sample tubes; thus, reference intervals must be established for the collection tubes used in each laboratory. Furthermore, a considerable difference was observed between women using and not using COCs.

Assessment of Rotational Thromboelastometry and Thrombin Generation Assay to Identify Risk of High Blood Loss and Re-Operation After Cardiac Surgery

Introduction: We aimed to investigate parameters for prediction of post-operative blood loss and re-operation in patients who underwent cardiopulmonary bypass. Methods: Thrombin generation assay, activated partial thromboplastin time, activated clotting time and rotational thromboelastometry (ROTEM) tests were performed at 4 time points in 65 patients: before skin incision (T1), after heparin injection (T2), after protamine reversal (T3) and before skin closure (T4). Results: Pre-operative endogenous thrombin potential (ETP) and peak thrombin levels were significantly lower in patients with high post-operative blood loss (≥ 800 mL) within 24 h than in those with low blood loss (< 800 mL). Clotting time (CT), maximal clotting firmness, clotting firmness time and alpha angle values of ROTEM measured at T2, T3 or T4 were significant predictors for high post-operative blood loss. An increase in CT-EXTEM over 4 time points was significant in patients who had a re-operation within 48 h compared to their counterparts. Conclusions: This study indicates that pre-operative ETP could predict high post-operative blood loss and that intra-operative ROTEM also helps to stratify risks of high post-operative blood loss and re-operation.

Thrombin Generation Assay and Hemostatic Profile for Elucidating Hypercoagulability in Endogenous Canine Hyperadrenocorticism

Canine hyperadrenocorticism is a common endocrine disorder caused by chronic secretion of glucocorticoid, often associated with hypercoagulability and secondary thrombosis. The thrombin generation assay (TGA) evaluates hemostasis globally by measuring endogenous thrombin potential. We aimed to determine whether TGA is suitable for assessing hypercoagulability in dogs with endogenous hyperadrenocorticism (HAC), and to correlate TGA with coagulation markers including fibrinogen, antithrombin (AT), D-dimer, prothrombin time (PT) and activated partial thromboplastin time (aPTT), and with routine laboratory tests for elucidating prothrombotic mechanisms and evaluating their utility as hypercoagulability screening tests. Thrombin generation performed with high activator concentration showed significantly higher endogenous thrombin potential (ETP) (P = .0239) and peak thrombin (P = .0281) in Cushing patients. Fibrinogen (P = <.0001) and AT (P = .0444) activities were significantly higher in the HAC group, while those of PT (P = .0046) and aPTT (P = .0002) were lower. Basal cortisol levels correlated positively with fibrinogen (r = 0.4503; P = .0355) and negatively with AT activity (r = -0.4580; P = .0280). Fibrinogen and hematocrit values were inversely correlated (r = -0.4853; P = .0076). Our study confirmed the presence of higher thrombin generation in dogs with HAC. However, TGA performed with lower activator concentrations was unsuitable for detecting hypercoagulability. Higher AT and fibrinogen levels and lower aPTT activity were identified in dogs with HAC relative to controls suggesting a potential role for the combined use of these assays when assessing hypercoagulability in canine hyperadrenocorticism.

Thrombin generation in children using ThromboScreen reagent kit with ST Genesia-A pilot study

INTRODUCTION

Thrombin generation assays assess overall coagulation system and are widely used in research; however, they still need standardization and clinical validation. The new ST Genesia is a benchtop, automated analyzer that normalizes each thrombin generation parameter using a reference plasma. The ThromboScreen reagent kit has two triggers, one of which contains thrombomodulin to assess the effect of the protein C pathway. This study aimed to make a pilot approach to the ThromboScreen reference range in children and evaluate the impact of sex, age, and pro- and anticoagulant plasma proteins on thrombin generation parameters.

METHODS

This study included 55 healthy children from the following age groups: 1-6 years (n = 14), 7-11 years (n = 15), and 12-17 years (n = 26). Children younger than 1 year were excluded from the study. We measured thrombin generation using ThromboScreen, coagulation routine and test, pro- and anticoagulant proteins.

RESULTS

Age did not influence ThromboScreen results. Males showed significantly lower endogenous thrombin potential and peak height values than females. The strongest determinants of endogenous thrombin potential were von Willebrand factor parameters, whereas for endogenous thrombin potential inhibition, the strongest determinants were protein C and protein S. No statistically significant differences were found between groups on temporal parameters.

CONCLUSIONS

For the ThromboScreen reagent kit, it may not be necessary to subdivide reference ranges according to age for children (>1 year).

Impact of centrifugation on thrombin generation in healthy subjects and in patients treated with direct oral anticoagulants

INTRODUCTION

Double centrifugation before freezing is recommended before thrombin generation assays (TGA). However, this procedure is not mandatory for routine hemostasis tests, precluding the use of these samples for TGA. The aim of this study is to assess the impact of single and double centrifugation on TGA performed on frozen samples from healthy volunteers (HVs) and patients receiving direct oral anticoagulants (DOACs).

METHODS

Forty HVs and 57 patients receiving a DOAC (dabigatran, rivaroxaban, apixaban, or edoxaban) were included in this prospective double-center observational study. Blood was collected into 109 mmol/L citrated tubes and frozen at -70°C before TGA using ST Genesia with STG-DrugScreen reagent. Four pre-analytical conditions were studied: (A) single centrifugation (2000 g, 15 minutes) before freezing; (B) one centrifugation before freezing and another after thawing (2000 g, 15 minutes for both); (C) one centrifugation before freezing(2000 g, 15 minutes) and another after thawing (2000 g, 10 minutes); (D) double centrifugation (2000 g, 15 minutes) before freezing (reference). Centrifugation conditions (A), (B), and (C) were compared with the reference condition (D). Acceptable relative differences were defined at 6%, 8%, and 10% for normalized lag time, endogenous thrombin potential, and peak height, respectively.

RESULTS

Centrifugation conditions had a small but acceptable impact on HVs samples, but single centrifugation always resulted in unacceptable reductions in normalized lag times for DOAC samples. A second centrifugation after thawing permitted the recovery of acceptable differences for the three TGA parameters for edoxaban but not for apixaban, rivaroxaban, nor dabigatran.

CONCLUSION

Double centrifugation before freezing should remain the recommended pre-analytical condition before TGA.

Protein Labeling and Crosslinking by Covalent Aptamers

We developed a new approach to selectively modify native proteins in their biological environment using electrophilic covalent aptamers. These aptamers are generated through introduction of a proximity-driven electrophile at specific nucleotide sites. Using thrombin as a proof-of-concept, we demonstrate that covalent aptamers can selectively transfer a variety of functional handles and/or irreversibly crosslink to the target protein. This approach offers broad programmability and high target specificity. Furthermore, it addresses issues common to aptamers such as instability towards endogenous nucleases and residence times during target engagement. Covalent aptamers are new tools that enable specific protein modification and sensitive protein detection. Moreover, they provide prolonged, nuclease-resistant enzyme inhibition.

Patients with acute and chronic coronary syndromes have elevated long-term thrombin generation

Coronary artery disease is a leading cause of morbidity and mortality worldwide. Despite significant advances in revascularization strategies and antiplatelet therapy with aspirin and/or P2Y₁₂ receptor antagonist, patients with acute coronary syndrome (ACS) continue to be at long-term risk of further cardiovascular events. Besides platelet activation, the role of thrombin generation (TG) in atherothrombotic complications is widely recognized. In this study, we hypothesized that there is an elevation of coagulation activation persists beyond 12 months in patients with ACS and chronic coronary syndrome (CCS) when compared with healthy controls. We measured TG profiles of patients within 72 h after percutaneous coronary intervention, at 6-month, 12-month and 24-month. Our results demonstrated that TG of patients with ACS (n = 114) and CCS (n = 40) were persistently elevated when compared to healthy individuals (n = 50) in peak thrombin (ACS 273.1 nM vs CCS 287.3 nM vs healthy 234.3 nM) and velocity index (ACS 110.2 nM/min vs CCS 111.0 nM/min vs healthy 72.9 nM/min) at 24-month of follow-up. Our results suggest a rationale for addition of anticoagulation to antiplatelet therapy in preventing long-term ischemic events after ACS. Further research could clarify whether the use of TG parameters to enable risk stratification of patients at heightened long-term procoagulant risk who may benefit most from dual pathway inhibition.

Recommendations for the measurement of thrombin generation: Communication from the ISTH SSC Subcommittee on Lupus Anticoagulant/Antiphospholipid Antibodies

Thrombin generation (TG) assay is an overall assay to assess the functionality of the hemostatic system and may be a useful tool in diagnosing patients with hyper- and hypocoagulability. Lack of standardization in performing the assays contributes largely to poor correlation between assays and study results. The current lack of standardization remains a major issue in the setting of TG, as illustrated in a recent survey of the ISTH/SSC indicating differences in pre-, analytical, and post-analytical factors among users. These factors may considerably affect the between-laboratory reproducibility of results. Based on the results of the survey and a current review of the literature, along with insights and strong consensus of key investigators in the field, we present guidance for measurement of TG in a clinical setting. Recommendations on blood drawing, handling, processing, and sample storage; reagent concentration and source; analytical conditions on dilution of samples and temperature; calibration and replicate testing; calculation and interpretation of results; and reference values are addressed to help in reducing interlaboratory variation. These recommendations aim at harmonization between methods and laboratories to support the application of TG in patient diagnosis and management.

Role of a thrombin generation assay in the prediction of infection severity

Thrombin plays a central role in sepsis pathophysiology. The correlation of thrombin generation (TG) assays with infection severity and prognosis, and whether it can be used as a clinical tool, have been poorly explored and are the subjects of our research. We recruited 130 patients with systemic infection between 2016 and 2019. Patients were divided according to infection severity by using the sequential organ failure assessment (SOFA) and quickSOFA (qSOFA) scores. The hemostatic state was analyzed by Calibrated Automated Thrombogram. The primary end points were TG values and the secondary end point was in-hospital mortality. Patients with qSOFA ≥ 2 had a longer lag time (5.6 vs. 4.6 min) and time to peak (8 vs. 6.9 min) than those with lower scores (p = 0.014 and 0.01, respectively). SOFA ≥ 2 had a longer lag time (5.2 vs. 4.3 min), time to peak (7.5 vs. 6.7 min) and lower endogenous thrombin potential (ETP) (1834 vs. 2015 nM*min), p = 0.008, 0.019, and 0.048, respectively. Patients who died (11) had lower ETP (1648 vs. 1928 nM*min) and peak height (284 vs. 345 nM), p = 0.034 and 0.012, respectively. In conclusion TG assays may be a valuable tool in predicting infection severity and prognosis.

Role of thrombin generation assays in the diagnosis of acute myocarditis and non-ST myocardial infarction

Myocarditis and myocardial infarction share a common clinical characteristics despite significant differences in etiology and pathogenesis. Current guidelines recommend using cardiac magnetic resonance imaging (MRI) or endocardial biopsy for a definite diagnosis; however, these guidelines are not fully implemented due to the high cost and low availability. We used a thrombin generation assay and simple blood test to characterize both diseases. We conducted a cross-sectional study from April to December 2018. Patients with initial clinical suspicions of non-ST elevation myocardial infarction (NSTEMI) or myocarditis were eligible. All patients were recruited prior to anticoagulant treatment. Patients in both groups underwent acceptable standard clinical evaluation. Twenty-eight patients were enrolled; 12 patients in the NSTEMI group and 16 in the myocarditis group. Patients in the NSTEMI group were significantly older than those in the myocarditis group (64.25 ± 9.67 vs. 37.94 ± 19.66 years, p < 0.01, respectively) with a higher prevalence of hyperlipidemia, diabetes mellitus, and ischemic heart disease (p < 0.01 for all). There was no difference between the groups regarding INR, PT, aPTT, and serum levels of creatinine, urea, CPK, troponin, and fibrinogen. Endogenous thrombin potential (ETP), which represents the total thrombin concentration in the plasma, was significantly higher in the myocarditis group than in the NSTEMI group (2091.88 ± 336.41 vs. 1860.75 ± 438.02 nM × min, p < 0.03). Myocarditis and myocardial infarction have a different pattern of thrombin generation Thrombogram. The myocarditis group had significantly higher plasma ETP than the NSTEMI group. This finding requires further evaluation to define a numerical threshold, thus avoiding invasive or expensive assessment of myocarditis.

Added Value of Blood Cells in Thrombin Generation Testing

The capacity of blood to form thrombin is a critical determinant of coagulability. Plasma thrombin generation (TG), a test that probes the capacity of plasma to form thrombin, has improved our knowledge of the coagulation system and shows promising utility in coagulation management. Although plasma TG gives comprehensive insights into the function of pro- and anticoagulation drivers, it does not measure the role of blood cells in TG. In this literature review, we discuss currently available continuous TG tests that can reflect the involvement of blood cells in coagulation, in particular the fluorogenic assays that allow continuous measurement in platelet-rich plasma and whole blood. We also provide an overview about the influence of blood cells on blood coagulation, with emphasis on the direct influence of blood cells on TG. Platelets accelerate the initiation and velocity of TG by phosphatidylserine exposure, granule content release and surface receptor interaction with coagulation proteins. Erythrocytes are also major providers of phosphatidylserine, and erythrocyte membranes trigger contact activation. Furthermore, leukocytes and cancer cells may be important players in cell-mediated coagulation because, under certain conditions, they express tissue factor, release procoagulant components and can induce platelet activation. We argue that testing TG in the presence of blood cells may be useful to distinguish blood cell-related coagulation disorders. However, it should also be noted that these blood cell-dependent TG assays are not clinically validated. Further standardization and validation studies are needed to explore their clinical usefulness.

Prophylactic fresh frozen plasma and platelet transfusion have a prothrombotic effect in patients with liver disease

BACKGROUND AND AIMS

Patients with liver disease acquire complex changes in their hemostatic system, resulting in prolongation of the international normalized ratio and thrombocytopenia. Abnormalities in these tests are commonly corrected with fresh frozen plasma (FFP) or platelet transfusions before invasive procedures. Whether these prophylactic transfusions are beneficial and truly indicated is increasingly debated. In this study, we studied ex vivo effects of FFP and platelet transfusions in patients with liver disease-associated hemostatic changes in a real-life clinical setting.

METHODS

We included 19 patients who were deemed to require prophylactic FFP transfusion by their treating physician and 13 that were prescribed platelet transfusion before a procedure. Hemostatic status was assessed in blood samples taken before and after transfusion and compared with healthy controls (n = 20).

RESULTS

Ex vivo thrombin generation was preserved in patients with liver disease before FFP transfusion. Following FFP transfusion, both in and ex vivo thrombin generation significantly increased, as evidenced by a 92% and 38% increase in thrombin-antithrombin and prothrombin fragment 1 + 2 levels, respectively, and a 20% increase in endogenous thrombin potential. Platelet counts increased from 28 [21-41] × 109 /L before to 43 [39-64] × 109 /L after platelet transfusion (P < .01), and was accompanied by increases in in vivo markers of hemostatic activation.

CONCLUSIONS

FFP and platelet transfusion resulted in increased thrombin generation and platelet counts in patients with liver disease, indicating a prothrombotic effect. However, whether all transfusions were truly indicated and had a clinically relevant effect is questionable.

Time Course of Inflammatory and Procoagulant Markers in the Early Period After Total Hip Replacement

Our study aimed to investigate the levels and time-course of systemic inflammatory and hemostasis markers in the early postoperative period in patients undergoing total hip replacement (THR). The study included 70 patients of both sexes, average age 68.4 ± 10.9 years. Levels of inflammatory and hemostasis markers were measured before surgery (POD 0), a day after the surgery (POD 1) and 5 days after surgery (POD 5). In the postoperative period inflammatory markers increased. The operation provoked a significant increase of CRP on POD 1 in comparison to POD 0 (68.5 ± 5.4 vs 6.8 ± 2.2 μg/mL, p < 0.001) and the additional increase was registered on POD 5 (87.5 ± 8.1 vs 68.5 ± 5.4 μg/mL, p < 0.001). Interleukin-6 significantly increased on POD 1 (251.5 ± 21.6 vs 14.6 ± 7.1 μg/mL, p < 0.001) and after that (POD 5) decreased. After surgery leukocyte count, neutrophil/lymphocyte ratio and platelet/lymphocyte ratio were significantly higher compared to POD 0. Activation of coagulation in the postoperative period was shown by increased peak thrombin on POD 5 in comparison to POD 0 (185 ± 27 vs. 124 ± 31 nM, p < 0.001). D-dimer was increased on POD 1 and an additional rise was observed on POD 5. vWF also progressively increased in the observed period. Results of our study showed that after THR systemic inflammatory markers increased and coagulation function was enhanced. Determination of inflammatory and procoagulant markers could help identify patients at risk for cardiovascular thromboembolic events.

Clot waveform analysis for perioperative hemostatic monitoring of arthroscopic synovectomy in a pediatric patient with hemophilia A and inhibitor receiving emicizumab prophylaxis

Emicizumab reduces bleeding in patients with hemophilia A and inhibitors (PwHA-I). Coagulation potential during the perioperative period in emicizumab-treated PwHA-I undergoing surgery remains to be evaluated. We describe a 14-year-old boy with HA-I receiving emicizumab prophylaxis who experienced arthroscopic synovectomy. He was treated with a bolus infusion of recombinant factor VIIa (rFVIIa; 80 μg/kg) immediately before surgery, and treatment continued at the same dose every 3 h on day 1, every 4 h on day 2, and every 6 h on day 3. Treatment with rFVIIa was discontinued on day 4. No perioperative bleeding or thrombotic events were observed. Coagulation potential throughout the perioperative period was retrospectively assessed with an easy-to-use clot waveform analysis (CWA). Measurements from CWA returned to within or near the normal range, suggesting successful hemostatic management. Coagulation potentials assessed by CWA showed a significant correspondence with those from a thrombin generation assay (TGA) that is already in use. CWA and TGA could both provide useful data for assessing coagulation potential in the perioperative hemostatic management of emicizumab-treated PwHA-I.

Pediatric Fibrinogen PART I-Pitfalls in Fibrinogen Evaluation and Use of Fibrinogen Replacement Products in Children

Fibrinogen is a key coagulation protein, playing a critical role in hemostasis. It is the first factor to decrease to critical levels during bleeding. Hypofibrinogenemia is an important risk factor for bleeding in clinical settings, including pediatric surgery. Yet, the optimal measurement of fibrinogen levels is subject to debate, as is the critical threshold for intervention. Fibrinogen replacement may be provided by cryoprecipitate and fibrinogen concentrate. Whilst both products contain fibrinogen, they are not equivalent, each has its own advantages and disadvantages, especially for pediatric use. Unfortunately, medical literature to support fibrinogen replacement in children is limited. In this article we review the current diagnostic tools to measure fibrinogen, with respect to their use in the pediatric critical care setting. Secondly, we evaluate the different fibrinogen replacement therapies, focusing on cryoprecipitate and fibrinogen concentrate and examine their individual product characteristics, associated risks and benefits, different dosing strategies and specific pitfalls for use in children. We summarize by highlighting current knowledge gaps and areas for future research.

Combined thrombogenic effects of vessel injury, pregnancy and procoagulant immune globulin administration in mice

Background

Pregnant women are at increased risk of thrombotic adverse events. Plasma derived immune globulin (IG) products, which are used in pregnancy for various indications, may contain procoagulant impurity activated coagulation factor XI (FXIa). Procoagulant IG products have been associated with increased thrombogenicity but their effect in pregnancy is unknown.

Methods

Late pregnant (gestation days 17–20) or early lactation (days 1–3) and control female mice were treated with IGs supplemented with human FXIa then subjected to ferric chloride (FeCl₃) vessel injury. Occlusion of blood vessel was assessed by recording blood velocity in the femoral vein for 20 min using doppler ultrasound laser imaging. FXIa dose was selected by the ability to increase thrombin generation in mouse plasma in vitro.

Results

FXIa produced robust thrombin generation in mouse plasma ex vivo. Following FeCl₃ injury, pregnant and non-pregnant mice receiving IG + FXIa exhibited faster reduction of blood velocity in femoral vein compared to IG alone or untreated controls. In vitro, thrombin generation in plasma samples collected after thrombosis in FXIa-treated animals was elevated and could be reduced by anti-FXI antibody.

Conclusions

Our results suggest that intravenously-administered FXIa may contribute to thrombosis at the site of vascular injury in both pregnant and non-pregnant animals.

Supplementary Information

Supplementary information accompanies this paper at 10.1186/s12959-020-00245-8.

In Silico Hemostasis Modeling and Prediction

Computational physiology, i.e., reproduction of physiological (and, by extension, pathophysiological) processes in silico, could be considered one of the major goals in computational biology. One might use computers to simulate molecular interactions, enzyme kinetics, gene expression, or whole networks of biochemical reactions, but it is (patho)physiological meaning that is usually the meaningful goal of the research even when a single enzyme is its subject. Although exponential rise in the use of computational and mathematical models in the field of hemostasis and thrombosis began in the 1980s (first for blood coagulation, then for platelet adhesion, and finally for platelet signal transduction), the majority of their successful applications are still focused on simulating the elements of the hemostatic system rather than the total (patho)physiological response in situ. Here we discuss the state of the art, the state of the progress toward the efficient "virtual thrombus formation," and what one can already get from the existing models.

Thrombin generation's role in predicting coronary disease severity

BACKGROUND

Thrombin, a key enzyme of the clotting system, is involved in thrombus formation, platelet activation, and atherosclerosis, thereby possessing a central role in the pathogenesis of ischemic heart disease. Studies have shown an association between thrombin generation (TG) and cardiovascular morbidity and mortality, but results have been equivocal. Our aim was to study the predictive ability of TG assay in evaluating coronary stenosis severity.

METHODS

In this prospective study we recruited patients with acute coronary syndrome (ACS) or acute chest pain (without evidence of myocardial injury) planned for coronary angiography. Thrombin generation was evaluated by Calibrated Automated Thrombogram (CAT) prior to angiography. Primary end points were significant coronary stenosis and the Syntax I score evaluated by coronary angiography.

RESULTS

From April 2018 through September 2019, we recruited 128 patients. In the primary analysis there was no significant association between TG and significant coronary stenosis nor between TG and syntax I score, however, there was a positive correlation between peak height and troponin peak (Spearman correlation coefficient 0.194, P-value = 0.035). In sub-group analysis, the chest pain group bare no association between TG and coronary stenosis. In unstable angina group there was an association between peak height and significant coronary stenosis (P-value = 0.029), and in non ST-elevation myocardial infarction group, TG values possessed a relatively good predictive ability of significant coronary stenosis (area under the receiver operating characteristic curve of ~65%) and a positive correlation between both lag time and ttpeak with the syntax I score was noticed (Spearman correlation coefficient 0.31, P-value = 0.099 and Spearman correlation coefficient 0.37, P-value = 0.045 respectively).

CONCLUSION

In patients with acute chest pain, TG values, evaluated by CAT, do not predict severity of coronary stenosis, nor do they possess prognostic value. Yet, in ACS patients, TG may have the ability to predict coronary disease severity.

Evaluation of Bleeding Phenotype of Inherited Factor VII Deficiency in Children With a Bleeding Assessment Tool and Global Assays

INTRODUCTION

Inherited factor VII (FVII) deficiency is the most common of the rare bleeding disorders and shows a heterogenous distribution of bleeding phenotypes independent of factor activity level. The bleeding score (BS) evaluates the phenotype of patients with rare bleeding disorders. Thromboelastography (TEG) and thrombin generation assays (TGAs) are 2 methods to evaluate global hemostasis, and controversially both tests are useful for identifying different bleeding tendency phenotypes. The purpose of this study was to investigate the use of the BS and global assays (TEG and TGAs) to predict the bleeding phenotype of inherited FVII deficiency.

MATERIALS AND METHODS

A total of 27 patients with FVII deficiency were evaluated with the BS and global hemostasis assays.

RESULTS

The BS was compatible with disease severity according to the FVII activity level (P<0.05) but the BS and bleeding grade of patients did not show a statistically significant correlation with factor activity level (P>0.05). No significant correlation was observed between the factor activity level and any TEG parameter (P>0.05). The factor activity level was negatively correlated with the lag time of the TGA on the contrary positively correlated with the peak thrombin time of the TGA (P<0.05).

CONCLUSIONS

The global assays do not successfully predict the bleeding phenotype. The BS is a more suitable tool than conventional and global assays for predicting the bleeding phenotype.

A risk score for prediction of venous thromboembolism in gynecologic cancer: The Thrombogyn score

BACKGROUND

Gynecologic cancers are associated with high rates of venous thromboembolism (VTE), which is exacerbated by pelvic surgery and chemotherapy.

OBJECTIVES

The aim of this study was to develop and validate a risk score for VTE in patients with gynecologic cancer and to test the predictive ability of the score following addition of procoagulant biomarker data.

PATIENTS AND METHODS

Clinical and laboratory variables were used to develop a risk score for the prediction of VTE in patients with gynecological cancer (n = 616), which was validated in a separate cohort of patients (n = 406). Endogenous thrombin potential and D-dimer levels were determined in a subset (n = 290) of patients and used to produce an extended score in the validation cohort.

RESULTS

Multivariable regression analysis identified BMI >30, hemoglobin <11.5 g/dL and chemotherapy as independent predictors of VTE, which formed the Thrombogyn score. Following competing risk regression analysis, subdistribution hazard ratios (SHRs), adjusted for cancer stage, were 8.16 (95% confidence interval [CI], 1.69-43.77) in the high-risk group (score = 2-3) and 4.12 (95% CI, 0.85-20.15) in the intermediate-risk group (score = 1) compared with the low-risk group (score = 0). SHRs for the validation cohort were 6.26 (95% CI, 1.24-31.39) and 3.00 (95% CI, 0.67-13.32), respectively. Cumulative incidence of VTE in the validation cohort high-risk group was 10.34% (95% CI, 6.51-16.41) per women-years compared with 1.06% (95% CI, 0.26-4.26) in the low-risk group. Using the extended Thrombogyn score, adjusted SHRs were 16.83 (95% CI, 4.20-67.37) in the high-risk group with a cumulative incidence of 21.15% (95% CI, 10.32-45.24). External validation of the score is required.

CONCLUSIONS

The Thrombogyn score identifies patients with gynecologic cancer at high and low risk of VTE. Addition of biomarker data improves the predictive power of the score.

Reference values for thrombin dynamics in platelet rich plasma

Thrombin generation (TG) is a better determinant of the overall function of the hemostatic system than routinely used clotting time-based assays and can be studied more in detail by thrombin dynamics analysis. Platelet poor plasma is often used to measure TG, however, measuring the contribution of the platelets is also important as patients with a low platelet count or with dysfunctional platelets have an increased risk of developing bleeding. In this study, platelet rich plasma (PRP) was collected from 117 healthy individuals. PRP was measured undiluted and diluted to a varying platelet concentration of 10*10⁹/L to 400*10⁹/L. Prothrombin conversion and thrombin inactivation were calculated from the data obtained by the TG parameters and coagulation factor levels (antithrombin, α₂Macroglobulin (α₂M) and fibrinogen). Reference ranges of TG and thrombin dynamics in PRP of 117 healthy individuals were established. Peak, velocity index and the maximum rate of prothrombin conversion increased linearly with platelet count, but endogenous thrombin potential reached a maximum at 150*10⁹/L as seen in a subset population (n = 20). More extensive analysis revealed that a platelet count below 50*10⁹/L did not affect TG parameters (except for the ETP). Correlation analysis indicated that the platelet count mainly affected the rate of prothrombin conversion. Inhibition of thrombin by antithrombin and α₂M increased with increasing TG, but the ratio of inhibition by antithrombin or α₂M remained the same independently of the total thrombin formed. In conclusion, TG and thrombin dynamics were assessed in PRP of healthy donors to provide reference values for future TG studies in PRP. Increasing the platelet count mainly affected the rate of prothrombin conversion and TG, rather than the total amount of thrombin formed.

From Classical Laboratory Parameters to Novel Biomarkers for the Diagnosis of Venous Thrombosis

Venous thrombosis is a common and potentially fatal disease, because of its high morbidity and mortality, especially in hospitalized patients. To establish the diagnosis of venous thrombosis, in the last years, a multi-modality approach that involves not only imaging modalities but also serology has been evolving. Multiple studies have demonstrated the use of some biomarkers, such as D-dimer, selectins, microparticles or inflammatory cytokines, for the diagnosis and treatment of venous thrombosis, but there is no single biomarker available to exclusively confirm the diagnosis of venous thrombosis. Considering the fact that there are some issues surrounding the management of patients with venous thrombosis and the duration of treatment, recent studies support the idea that these biomarkers may help guide the length of appropriate anticoagulation treatment, by identifying patients at high risk of recurrence. At the same time, biomarkers may help predict thrombus evolution, potentially identifying patients that would benefit from more aggressive therapies. This review focuses on classic and novel biomarkers currently under investigation, discussing their diagnostic performance and potential benefit in guiding the therapy for venous thrombosis.

The effect of pH on thrombin generation-An unrecognized potential source of variation

BACKGROUND

When CO2 escapes from plasma, the pH of the plasma increases. In samples left open or kept in long-term storage, the pH may increase considerably. Assays in which the ratio of plasma sample relative to the total volume including reagents is high may be sensitive to the pH of the plasma sample.

OBJECTIVE

The aim was to investigate the effect of the pH of plasma samples used in the calibrated automated thrombin generation (CAT) assay in which the ratio (plasma sample) / (total volume) is high.

METHODS

Plasma pH was increased by allowing CO2 to escape in open beakers before the CAT analysis. The effect of pH was also investigated by mixing plasma with buffers with different pH levels.

RESULTS

At a pH close to 8.0, endogenous thrombin potential (ETP) and peak decreased considerably, whereas lagtime and time-to-peak were modestly increased. Mixtures of plasma and buffer with pH levels between 7 and 8 showed that ETP and peak decreased at alkaline pH; lagtime and time-to-peak were higher at acidic pH levels but were shortened, partly in contrast to first results, at alkaline pH levels. The addition of 4-(2-hydroxyethyl)-1-piperazineethanesulfonic acid buffer to plasma with a high pH attenuated the effects; however, the effect was most significant if added before the CO2 escaped.

CONCLUSION

Modifications of plasma pH can significantly alter thrombin generation. In alkaline samples, for example, after lengthy storage in a freezer where pH can increase considerably, thrombin generation is lowered. To minimize this effect, plasma should be stored in tubes filled to the maximum volume.

Global coagulation assays in hemophilia A: A comparison to conventional assays

BACKGROUND

Global assays measure the interactions of coagulants, anticoagulants, and platelets on thrombin generation and may reflect the comprehensive coagulation potential in patients with hemophilia better than conventional assays.

OBJECTIVES

The objectives of the current study were to investigate the value of global assays for measuring and monitoring the coagulation potential of patients with hemophilia A (HA).

PATIENTS/METHODS

Rotational thromboelastometry, thrombin generation assay (TGA), and activated partial thromboplastin time (APTT) clot waveform analysis were investigated in a cohort of patients with severe, moderate, and mild HA and compared with conventional assays.

RESULTS

The maximum velocity (MaxVel) parameter of modified thromboelastometry analysis, initiated by tissue factor and in the presence of corn trypsin inhibitor (CTI), had 92% sensitivity and 95% specificity for hemophilia diagnosis. The MaxVel also strongly correlated with factor VIII (FVIII) levels of patients with HA (r = .805, P < .0001). CTI improved the sensitivity of TGA, providing more accurate results. In particular, peak height parameter of platelet-rich plasma samples with CTI had a sensitivity and specificity of 100% and 94%, respectively, in all patients with HA. APTT clot waveform analysis minimum value of first derivative (Min1) and minimum value of second derivative (Min2) parameters (representing speed and acceleration of clot formation, respectively) were sensitive and correlated more strongly with FVIII levels than APTT clotting times did (Min1: r = 0.786, P < 0.0001; Min2: r = 0.759, P < 0.0001; APTT: r = -0.513, P = 0.001).

CONCLUSIONS

The sensitivity and specificity of the global assays was method dependent. Correlation between clinical end points and thrombin generation might also be valuable in the era of non-factor replacement therapy.

Kaolin, used to trigger coagulation in thrombin generation test, increases sensitivity of the method in hemophilia patients

: Thrombin generation test (TGT) is well established tool to research blood coagulation in plasma of hemophilia patients. Traditionally coagulation in this test is triggered by a tissue factor (TF), an extrinsic coagulation pathway activator. However, it is known that disorders of the intrinsic pathway are most important for coagulation in hemophilia. In this study, we hypothesized that triggering coagulation via the intrinsic pathway could increase a sensitivity of the TGT to monitor hemophilia treatment. The aim of this study was to compare thrombin generation in hemophilia A patients with inhibitors to factor VIII before and after infusion of bypassing agent [recombinant-activated factor VIIa (rVIIa)] using standard activation of coagulation by TF or by kaolin, an activator of coagulation by intrinsic pathway. Endogenous thrombin potential (ETP) in nine patients was measured. ETP before (ETP0) and 60 min after rVIIa infusion (ETP60) were compared. It was shown that ETP0 and ETP60 were significantly different when using any coagulation activator (paired Student's t test, P = 0.017 and 3.7 × 10 for clotting activation by TF and kaolin, respectively). The ratios of ETP60/ETP0 were 1.2 ± 0.2 or 30.0 ± 22.4 (mean ± SD, n = 9) for coagulation activated by TF or kaolin, respectively, and were significantly different (paired Student's t test, P < 0.005). The TGT clearly distinguished between ETP0 and ETP60 in the case of any coagulation activator, but ETP increasing after rVIIa infusion was significantly higher when activated with kaolin. This provided increased sensitivity of this method for monitoring hemophilia therapy.

Mode of Delivery Does Not Influence Postpartum Hypercoagulability Measured by Thrombin Generation or Thromboelastometry

Introduction  Venous thromboembolism (VTE) is a significant cause of maternal mortality with the greatest risk postpartum. Mode of delivery influences VTE risk, with emergency caesarean section (CS) associated with the highest risk (CS). Thromboprophylaxis is recommended for selected women to reduce the risk of VTE.

We aimed to investigate the impact of mode of delivery and thromboprophylaxis on hypercoagulability as measured by thromboelastometry (TEM) and thrombin generation (TG) in women at high VTE risk.

Materials and Methods  Blood was collected from 99 pregnant women with VTE risk factors at up to five time points from pre- (T1) and post (T2)-delivery to 6 weeks postpartum (T5). Multiple linear regression was utilised to compare TG and TEM between those with vaginal delivery (VD) and CS at each time point. Paired sample t -test with post hoc Bonferroni correction was utilised to compare laboratory markers over time.

Results  Women in both groups had a median of three postpartum VTE risk factors, with higher body mass index and parity post-VD. In both the groups, TG and TEM parameters suggested hypercoagulability at T2 compared with T1, with resolution at T5. There were minimal differences between groups, apart from T2 with shorter clot formation time and higher maximum clot firmness in the VD group.

Conclusion  TG and TEM illustrate hypercoagulability associated with pregnancy and delivery. The pattern of postpartum hypercoagulability seen in women with VTE risk factors was similar irrespective of mode of delivery. Further research is required to establish the effect of labour on TG/TEM in the absence of low molecular weight heparin use.

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.

Effect of storage of plasma in the presence of red blood cells and platelets: re-evaluating the shelf life of whole blood

BACKGROUND

There is renewed interest in administering whole blood (WB) for the resuscitation of patients with bleeding trauma. The shelf life of WB was established decades ago based on the viability of red blood cells. However, plasma quality during WB storage is not established.

STUDY DESIGN AND METHODS

White blood cell- and platelet-reduced WB (WB-PLT) was prepared using standard processes and compared to WB processed using a platelet-sparing WBC reduction (WB + PLT) filter. WB (± PLT) was held at 2 to 6°C for 35 days alongside control units of red blood cells (RBCs) in saline, adenine, glucose, and mannitol and liquid plasma. A series of assays explored the coagulation potential and RBC quality.

RESULTS

While fibrinogen and α2-antiplasmin remained unaffected by storage, other factors varied between components or over time at 2 to 6°C. At 14 days factor V, factor VII, α₂ -antiplasmin and free protein S antigen remained on average greater than 0.50 IU/mL or 50%, as appropriate, in WB ± PLT. Factor VIII was on average 0.49 IU/mL in WB+PLT, and 0.56 IU/mL for WB-PLT. Free protein S activity decreased significantly in all arms but remained on average greater than 40% at Day 14. Contact activation was not demonstrated before Day 14. Thrombin generation in plasma remained relatively stable to Day 35 in all arms.

CONCLUSIONS

Clotting factor activity remained at or above a mean of 0.5 IU/mL, or 50%, at Day 14 for factor V, factor VII, factor VIII, free protein S, fibrinogen, and α2-antiplasmin in all arms. Further data on platelet function in WB+PLT is needed to inform its shelf life.

Assessing the impact of product inhibition in a chromogenic assay

Chromogenic substrates (CS) are synthetic substrates used to monitor the activity of a target enzyme. It has been reported that some CSs display competitive product inhibition with their target enzyme. Thus, in assays where enzyme activity is continuously monitored over long periods of time, the product inhibition may significantly interfere with the reactions being monitored. Despite this knowledge, it is rare for CSs to be directly incorporated into mathematical models that simulate these assays. This devalues the predictive power of the models. In this study, we examined the interactions between a single enzyme, coagulation factor Xa, and its chromogenic substrate. We developed, and experimentally validated, a mathematical model of a chromogenic assay for factor Xa that explicitly included product inhibition from the CS. We employed Bayesian inference, in the form of Markov-Chain Monte Carlo, to estimate the strength of the product inhibition and other sources of uncertainty such as pipetting error and kinetic rate constants. Our model, together with carefully calibrated biochemistry experiments, allowed for full characterization of the strength and impact of product inhibition in the assay. The effect of CS product inhibition in more complex reaction mixtures was further explored using mathematical models.

Measurements of endogenous thrombin potential using the CAT method in cats: Reference values and influence of the direct factor Xa inhibitor apixaban

The aim of this study was to establish a thrombin generation assay (calibrated automated thrombogram, CAT) in cats by determining the precision (repeatability), reference values, and the sensitivity to anticoagulant treatment with the factor Xa inhibitor apixaban. The CAT method was performed on citrated plasma with different commercial tissue factor (TF) reagents (PPP Reagent 1 pM [LOW], PPP Reagent 5 pM, PPP Reagent 20 pM [HIGH]) according to the manufacturers` test instruction. Measurements in triplicate were performed in platelet poor plasma (PPP) of 58 healthy cats and in 6 cats at different times following the oral administration of 2.5 mg apixaban. The median CVs in healthy cats usually were < 10% with the exception of thrombin peak height measured using PPP Reagent 1 pM (14.6%). Reference values of all parameters showed marked inter-individual variability and depended largely on the TF concentration of the used activating reagent. Thrombin generation was significantly influenced by apixaban and reacted more sensitively than other tests of haemostasis including the prothrombin time, aPTT, and rotational elastometry. In conclusion, thrombin generation measured by the CAT method using commercially available reagents seems suitable for the examination of feline PPP and may be a valuable method to establish effective anticoagulant therapies for the feline patient and monitoring of such therapies in cats.

Assessment of the procoagulant potential and associated risk factors in pregnant patients with inflammatory bowel diseases

OBJECTIVE

Both inflammatory bowel diseases (IBDs) and pregnancy are established risk factors for thrombotic complications, thus IBD pregnant patients can be considered at even greater risk for thrombosis as compared to non IBD pregnant women. We aimed to evaluate the risk factors associated with this prothrombotic tendency among IBD women throughout gestation.

METHODS

Women with IBD attending a multidisciplinary clinic for the preconception,antenatal and postnatal treatment were prospectively recruited during 2017-2018. Prothrombotic tendency was assessed by thrombin generation, a global marker of the activation of the coagulation system, expressed as the endogenous thrombin potential (ETP).

RESULTS

Overall, 145 IBD women and 50 healthy control subjects were enrolled in this study. Body mass index (BMI) and gestational age were comparable between the groups. ETP level was significantly higher in women with IBD compared to control subjects in all time period (P < .0001). Among women with IBD, ETP level positively correlated with disease activity, as assessed by physician global assessment (P = .005), gestational age (P < .0001), extra-intestinal involvement (P = .04), C-reactive protein level (P < .0001), erythrocyte sedimentation rate (P < .0001), white blood cell count (P = .008), BMI (P = .02) and was inversely correlated with hemoglobin level (P < .0001). ETP level did not correlate with the occurrence of adverse pregnancy outcomes. In a multivariate analysis, active disease (β = 0.20, P = .009), gestational age (β = 0.45, P < .0001), extra-intestinal involvement (β = 0.17, P = .02) and BMI (β = 0.15, P = .05) retained independent predictors of high ETP levels.

CONCLUSION

As determined by thrombin generation, the procoagulant potential among IBD pregnant patients was independently associated with disease activity, BMI and extra-intestinal disease involvement.

Hydroxychloroquine reverses the prothrombotic state in a mouse model of antiphospholipid syndrome: Role of reduced inflammation and endothelial dysfunction

Antiphospholipid antibodies (aPL) promote endothelial dysfunction, inflammation and procoagulant state. We investigated the effect of hydroxychloroquine (HCQ) on prothrombotic state and endothelial function in mice and in human aortic endothelial cells (HAEC). Human aPL were injected to C57BL/6 mice treated or not with HCQ. Vascular endothelial function and eNOS were assessed in isolated mesenteric arteries. Thrombosis was assessed both in vitro by measuring thrombin generation time (TGT) and tissue factor (TF) expression and in vivo by the measurement of the time to occlusion in carotid and the total thrombosis area in mesenteric arteries. TGT, TF, and VCAM1 expression were evaluated in HAEC. aPL increased VCAM-1 expression and reduced endothelium dependent relaxation to acetylcholine. In parallel, aPL shortened the time to occlusion and extended thrombus area in mice. This was associated with an overexpression of TF and an increased TGT in mice and in HAEC. HCQ reduced clot formation as well as TGT, and improved endothelial-dependent relaxations. Finally, HCQ increased the p-eNOS/eNOS ratio. This study provides new evidence that HCQ improves procoagulant status and vascular function in APS by modulating eNOS, leading to an improvement in the production of NO.