The endogenous thrombin potential and high levels of coagulation factor VIII, factor IX and factor XI

Thrombin worsens extravascular lung water and outcomes of septic patients with acute respiratory distress syndrome: A case control study

Endothelial cell (EC) activation may increase systemic vascular permeability, causing extravascular lung water (EVLW) in sepsis with acute respiratory distress syndrome (ARDS). However, the correlation between thrombin and EVLW in sepsis and ARDS has not yet been addressed. Patients with sepsis and ARDS were prospectively enrolled between 2014 and 2016, and EVLW and serum thrombin levels on days 1 and 3 were measured and compared between surviving and non-surviving patients. Additionally, morphological changes in human umbilical vein endothelial cells (HUVECs) in the serum of patients with high and low EVLW were evaluated. The levels of EVLW, endothelial cells, and thrombin may positively correlate with the survival of patients with severe sepsis and ARDS. Twenty-seven patients were enrolled, and baseline characteristics, including age, sex, Acute Physiology and Chronic Health Evaluation (APACHE) II, prior 24-h fluid balance, body mass index, and shock status, were similar between survivors and non-survivors; however, day 1 EVLW was higher in non-survivors (27.5 ± 8.4 vs 22 ± 6.5 mL/kg, P = .047). EVLW of survivors improved from day 1 to day 3 (22 ± 6.5 vs 11 ± 3.8 mL/kg, P < .001), but did not improve in non-survivors (27.5 ± 8.4 vs 28 ± 6.7 mL/kg, P = .086), which means that patients had significantly lower EVLW on day 3 than on day 1. Thrombin levels of survivors significantly improved (1.03 ± 0.55 vs 0.87 ± 0.25 U/mL, P = .04) but did not improve in non-survivors (1.97 ± 0.75 vs 2.2 ± 0.75 U/mL, P = .08) from day 1 to day 3. EVLW and thrombin levels were positively correlated (r2 = 0.71, P < .0001). In vitro, the morphology and junctions of HUVECs changed when the serum from patients with high EVLW was added. The intercellular distances among the control, high EVLW, and low EVLW groups were 5.25 ± 1.22, 21.33 ± 2.15, and 11.17 ± 1.64 µm, respectively (P < .05).

Activation of blood coagulation and thrombin generation in acute ischemic stroke treated with rtPA

The impact of thrombolysis with recombinant tissue plasminogen activator (rtPA) on blood coagulation in acute ischemic stroke (AIS) patients is not completely understood. We studied the effect of thrombolysis on the thrombin generation (TG) profile as well as coagulant activity of activated factors IX (FIXa), XI (FXIa) and tissue factor (TF) in AIS patients. In a case-control study, TG parameters as well as FIXa, FXIa and TF levels were assessed in 95 AIS patients, including individuals receiving rtPA treatment within 4.5 h since AIS onset (n = 71, 74.7%) and those ineligible for thrombolysis (n = 24, 25.3%). Blood samples were collected at baseline and after 24 h since admission. The two groups were similar with regard to demographics and clinical factors. In thrombolysed patients, all TG parameters measured after 24 h were markedly decreased, with strongest impact on lag time (LT), when compared with the baseline values (81.3% longer LT, p < 0.0001), as well as when compared to the non-thrombolysed group (86% longer LT, p = 0.002). In non-thrombolysed AIS patients the TG remained unaltered. Logistic regression adjusted for potential confounders showed that high baseline ETP value (the top quartile) was solely predicted by the presence of circulating FIXa, whereas after 24 h FXIa predicted high ETP in the subgroup of thrombolysed and in all AIS patients. Thrombolysis in AIS patients markedly attenuates the TG. Elevated FXIa contributes to thrombin formation capacity after 24 h, highlighting a role of this factor in the regulation of blood coagulation in AIS.

Anwendungen des endogenen Thrombinpotenzials

An overview is given on the method and the applications of thrombin generation assays. Thrombin generation assays provide a tool which can be used to trace the entire thrombin formation and inactivation of a plasma sample. Therefore they are principally different from traditional global assays like PT and aPTT and promise new opportunities for the assessment of bleeding or thrombotic risks.

Thrombin generation and rotational thromboelastometry in the healthy adult population

Published data on thrombin generation variables and their correlation with thrombo - elastometry in the healthy population are scarce. This study aimed at assessing thrombin generation in adults and its correlation to classical rotational thromboelastometry (ROTEM).

Thrombin generation was measured in platelet-poor plasma from healthy volunteers using the calibrated automated thrombogram (CAT) with 1 and 5 pmol/l tissue factor final concentration. Lag time, thrombin peak, time to thrombin peak and endogenous thrombin potential (ETP) were analyzed. ROTEM was performed without activator (NATEM) and data for clotting time, alpha angle, clot formation time and maximum clot firmness were correlated with those of thrombin generation.

Altogether 132 persons (72 men, 60 women; median age: 48.0 years) were included. There was a positive non-linear correlation for age versus lag time (p < 0.001) and time to peak (p = 0.001), and almost linear correlation for age versus thrombin peak (p = 0.024) and ETP (p = 0.001), although with a moderate regression slope. Regarding ROTEM, there was a positive correlation between age and maximum clot firmness and alpha angle (p = 0.001), but a negative correlation between age and clotting time (p = 0.039). Comparing both assays, thrombin peak and ETP measured with a final tissue factor concentration of 5 pmol/l correlated significantly with alpha angle and maximum clot firmness.

The age-related changes in CAT and ROTEM variables among adults are not linear. There is a significant correlation, although with a moderate slope, between data from CAT measured with 5 pmol/l tissue factor and ROTEM.

Identifying coagulopathies in the pathophysiology of cold stress syndrome in the Florida manatee Trichechus manatus latirostris

Cold stress syndrome (CSS) in the Florida manatee Trichechus manatus latirostris has been defined as morbidity and mortality resulting from prolonged exposure to water temperatures <20°C. The pathophysiology is described as multifactorial, involving nutritional, immunological and metabolic disturbances; however, the exact mechanisms are unknown. We hypothesized that thromboembolic complications contribute to the pathophysiology of CSS in addition to the previously described factors. During the winter of 2014-2015, 10 Florida manatees with clinical signs of CSS were presented to Lowry Park Zoo, Tampa, FL, USA. Thromboelastography (TEG) and coagulation panels were performed at admission. In addition, coagulation panel data from 23 retrospective CSS cases were included in the analyses. There were numerous differences between mean values of TEG and coagulation parameters for healthy manatees and those for CSS cases. Among TEG parameters, reaction time (R), clot formation time (K) and percentage of clot lysed after 30 min (LY30) values were significantly different (p < 0.05) between the 2 groups. CSS cases also had significantly higher mean D-dimer concentration and coagulation factor XI activity, prolonged mean activated partial thromboplastin time (aPTT) and significantly decreased mean antithrombin activity. These combined abnormalities include clinicopathologic criteria of disseminated intravascular coagulation, indicating an increased risk of thromboembolic disease associated with manatee CSS.

Correlation between factor (F)XIa, FIXa and tissue factor and trauma severity

BACKGROUND

It has been observed that trauma patients often display elevated procoagulant activity that could be caused, in part, by tissue factor (TF). We previously observed that trauma patients with thermal, blunt, and penetrating injuries have active FIXa and FXIa in their plasma. In the current study, we evaluated the effect of injury severity, with or without accompanying shock, on the frequency and concentration of TF, FIXa, and FXIa in plasma from trauma patients.

METHODS

Eighty trauma patients were enrolled and divided equally into four groups based on their Injury Severity Score and base deficit:Blood was collected at a 0 time-point (first blood draw upon arrival at hospital) and citrate plasma was prepared, frozen, and stored at -80 °C. FXIa, FIXa, and TF activity assays were based on a response of thrombin generation to corresponding monoclonal inhibitory antibodies.

RESULTS

The frequency and median concentrations of TF were relatively low in non-severe injury groups (17.5% and 0 pM, respectively) but were higher in those with severe injury (65% and 0.5 pM, respectively). Although FXIa was observed in 91% of samples and was high across all four groups, median concentrations were highest (by approximately fourfold) in groups with shock. FIXa was observed in 80% of plasma samples and concentrations varied in a relatively narrow range between all four groups. No endogenous activity was observed in plasma from healthy individuals.

CONCLUSIONS

(1) Frequency and concentration of TF is higher in patients with a higher trauma severity. (2) Concentration of FXIa is higher in patients with shock. (3) For the first time reported, the vast majority of plasma samples from trauma patients contain active FIXa and FXIa.

LEVEL OF EVIDENCE

Prognostic/epidemiological study, level II.

The heart as an extravascular target of endothelin-1 in particulate matter-induced cardiac dysfunction

Exposure to particulate matter air pollution has been causally linked to cardiovascular disease in humans. Several broad and overlapping hypotheses describing the biological mechanisms by which particulate matter exposure leads to cardiovascular disease have been explored, although linkage with specific factors or genes remains limited. These hypotheses may or may not also lead to particulate matter-induced cardiac dysfunction. Evidence pointing to autocrine/paracrine signaling systems as modulators of cardiac dysfunction has increased interest in the emerging role of endothelins as mediators of cardiac function following particulate matter exposure. Endothelin-1, a well-described small peptide expressed in the pulmonary and cardiovascular systems, is best known for its ability to constrict blood vessels, although it can also induce extravascular effects. Research on the role of endothelins in the context of air pollution has largely focused on vascular effects, with limited investigation of responses resulting from the direct effects of endothelins on cardiac tissue. This represents a significant knowledge gap in air pollution health effects research, given the abundance of endothelin receptors found on cardiac tissue and the ability of endothelin-1 to modulate cardiac contractility, heart rate, and rhythm. The plausibility of endothelin-1 as a mediator of particulate matter-induced cardiac dysfunction is further supported by the therapeutic utility of certain endothelin receptor antagonists. The present review examines the possibility that endothelin-1 release caused by exposure to PM directly modulates extravascular effects on the heart, deleteriously altering cardiac function.

Genetic risk factors for venous thrombosis in women using combined oral contraceptives: update of the PILGRIM study

Identifying women at risk of venous thrombosis (VT) under combined oral contraceptives (COC) is a major public health issue. The aim of this study was to investigate in COC users the impact on disease of genetic polymorphisms recently identified to associate with VT risk in the general population. Nine polymorphisms located on KNG1, F11, F5, F2, PROCR, FGG, TSPAN and SLC44A2 genes were genotyped in a sample of 766 patients and 464 controls as part of the PILGRIM (PILl Genetic Risk Monitoring) study. Cases were women who experienced an episode of documented VT during COC use, while controls were women with no history of VT using COC at the time of inclusion. Among the studied polymorphisms, only F11 rs2289252 was significantly associated with VT. The F11 rs2289252-A allele was associated with a 1.6-fold increased risk of VT (p < 0.0001). Besides, the combination of the rs2289252-A allele with non-O blood group, present in 52% of the cohort, was associated with an odds ratio of 4.00 (2.49-6.47; p < 10^-4 ). The consideration of this genetic risk factor could help to better assess the risk of VT in COC users.

Normal Hemostatic Profiles and Coagulation Factors in Healthy Free-Living Florida Manatees ( Trichechus manatus latirostris)

Hemostatic disorders presumptively play an important role in the pathophysiology of several important disease conditions in the Florida manatee ( Trichechus manatus latirostris). Prior to pursuing such clinical implications, it is essential to establish normal hemostatic profiles in clinically healthy animals. During annual health assessments of free-living manatees organized by the US Geological Survey, blood samples were collected from 12 healthy animals from the Atlantic coast and 28 from the Gulf of Mexico coast of Florida, with body lengths of 210-324 cm. The following analyses were performed on citrated plasma: prothrombin (PT), partial thromboplastin time (PTT), and concentrations of fibrinogen, D-dimers, and coagulation factors VII, VIII, IX, X, XI, and XII. Compared to other mammalian species, manatees had short PT (9.2±1.5 s) and PTT (10.7±0.5 s), fibrinogen was 369±78.7 mg/dL, antithrombin III was 132±11%, and D-dimer was 142±122 ng/mL. Baseline concentrations for the listed coagulation factors were established. When comparing coagulation factors between locations, Atlantic coast manatees had significantly higher factors VIII, IX, and X than did Gulf Coast manatees. This finding may reflect differences in water salinity, diet, or genetics. There were no differences in coagulation factors when among sexes and sizes. These baselines for hemostatic profiles and coagulation factors in healthy free-living manatees lay the foundation for diagnosis and future research of hemostatic disorders and contribute to understanding their role in the pathophysiology of manatees affected by various diseases.

Extracellular histones mediate the effects of metal-rich air particles on blood coagulation

BACKGROUND

Epidemiological studies have shown associations of particulate matter (PM) exposure with hypercoagulability and thrombosis. Extracellular circulating histones have recently been identified as novel mediators of inflammatory and procoagulant responses. The potential roles of extracellular histones in PM-related hypercoagulability have yet not been investigated.

OBJECTIVES

In 63 steel workers, we evaluated the effects of exposure to PM and PM metal components on two extracellular histone modifications (H3K4me3 and H3K9ac); and the association of H3K4me3 and H3K9ac with coagulation markers.

METHODS

Extracellular H3K4me3 and H3K9ac were determined in plasma through enzyme-linked immunosorbent assays. Coagulation markers included endogenous thrombin potentials (ETPs), tissue-type plasminogen activator antigen (t-PA) and D-dimer. Exposure to PM with aerodynamic diameters <1 μm (PM1) or <10 μm (PM10) and PM10 metal components were estimated for each participant.

RESULTS

The coagulation marker ETP, measured in the presence of soluble thrombomodulin (ETP TM+), showed significant positive associations with PM1 (β=107.84, p=0.03), PM10 (β=83.06, p=0.02), and zinc (β=75.14, p=0.03); and a marginal association with iron (β=122.58, p=0.07). Additional PM effects were observed on t-PA, D-dimer, and ETP TM+. PM1 exposure was associated with increased plasma H3K4me3 and H3K9ac (β=0.20, p=0.02; β=0.16, p=0.05, respectively). H3K4me3, but not H3K9ac, was associated with zinc (β=0.13, p=0.03) and iron (β=0.32, p=0.01) contained in PM. ETP TM+ was increased in association with higher plasma H3K4me3 (β=0.50, p=0.05) and H3K9ac (β=0.54, p=0.05).

CONCLUSIONS

This observational study suggests potential roles of extracellular histones in PM-induced hypercoagulability. Experimental studies are warranted to further characterize these findings.

Elevated factor IX activity is associated with an increased odds ratio for both arterial and venous thrombotic events

OBJECTIVES

Elevations of factor IX (FIX) are thought to contribute to thrombotic risk, but this has not been well characterized. We retrospectively sought to determine whether elevated FIX levels are a risk factor for thrombosis in 81 adult subjects younger than 65 years (mean, 47 years) who were referred for evaluation of a hypercoagulable state.

METHODS

Patients were classified by arterial transient ischemic attack/stroke (TIA/stroke, n = 62) or venous thromboembolism (VTE, n = 19) events. FIX activity testing was performed on all 81 subjects and a reference group of 40 healthy individuals.

RESULTS

Thirteen (21%) of 62 subjects with TIA/stroke and 5 (26%) of 19 subjects with VTE had elevated FIX activity. Odds ratios for TIA/stroke and VTE in subjects with elevated FIX activity were 3.7 (95% confidence interval [CI], 0.76-17.65) and 6.8 (95% CI, 1.18-39.07), respectively.

CONCLUSIONS

Our findings suggest an association between elevated FIX levels and both arterial and venous thrombotic events.

Blood hypomethylation of inflammatory genes mediates the effects of metal-rich airborne pollutants on blood coagulation

OBJECTIVES

Recent investigations have associated airborne particulate matter (PM) with increased coagulation and thrombosis, but underlying biological mechanisms are still incompletely characterised. DNA methylation is an environmentally sensitive mechanism of gene regulation that could potentially contribute to PM-induced hypercoagulability. We aimed to test whether altered methylation mediates environmental effects on coagulation.

METHODS

We investigated 63 steel workers exposed to a wide range of PM levels, as a work-related condition with well-characterised prothrombotic exposure. We measured personal PM10 (PM≤10 µm in aerodynamic diameter), PM1 (≤1 µm) and air metal components. We determined leukocyte DNA methylation of NOS3 (nitric-oxide-synthase-3) and EDN1 (endothelin-1) through bisulfite-pyrosequencing and we measured ETP as a global coagulation-activation test after standardised triggers.

RESULTS

ETP increased in association with PM10 (β=20.0, 95% CI 3.0 to 37.0), PM1 (β=80.8 95% CI 14.9 to 146.7) and zinc (β=51.3, 95% CI 0.01 to 111.1) exposures. NOS3 methylation was negatively associated with PM10 (β=-0.2, 95% CI -0.4 to -0.03), PM1 (β=-0.8, 95% CI -1.4 to -0.1), zinc (β=-0.9, 95% CI -1.4 to -0.3) and iron (β=-0.7, 95% CI -1.4 to -0.01) exposures. Zinc exposure was negatively associated with EDN1 (β=-0.3, 95% CI -0.8 to -0.1) methylation. Lower NOS3 (β=-42.3; p<0.001) and EDN1 (β=-14.5; p=0.05) were associated with higher ETP. Statistical mediation analysis formally confirmed NOS3 and EDN1 hypomethylation as intermediate mechanisms for PM-related coagulation effects.

CONCLUSIONS

Our study showed for the first time, that gene hypomethylation contributes to environmentally induced hypercoagulability.

Factors associated with the presence of circulating active tissue factor and activated factor XI in stable angina patients

Circulating active tissue factor (TF) and activated factor XI (FXIa) have been detected in subgroups of acute coronary syndromes (ACSs) and stable angina patients. We sought to evaluate the determinants of active TF and FXIa in stable angina patients. We studied 124 consecutive stable angina patients. Recent ACS, atrial fibrillation, and anticoagulant therapy were the exclusion criteria. Plasma active TF and FXIa were determined by measuring the response to inhibitory antibodies. T helper 1 lymphocyte (Th1) and Th2 responses were assessed in plasma by interleukin (IL)-4, IL-6, IL-8, IL-10, IL-18, interferon-γ, and tumor necrosis factor-α, oxidative stress by 8-isoprostaglandin F(2α) (8-iso-PGF(2α)), and coagulation by prothrombin fragments F1+2 (F1+2) and free TF pathway inhibitor (f-TFPI). TF and FXIa activity were detected in 25 (20.2%) and 49 (39.5%) stable angina patients, respectively. Both factors were found in 23 (18.5%) patients. Patients with detectable TF or FXIa had higher F1+2, 8-iso-PGF(2α), IL-6, but not other cytokines, and lower f-TFPI (all P < 0.001) compared with the remainder. There were no intergroup differences with regard to cardiovascular risk factors or medication. Multivariate analysis showed that F1+2 and f-TFPI were the only independent predictors of the TF presence, whereas 8-iso-PGF(2α) and F1+2 predicted the presence of FXIa in stable angina patients. In stable angina patients, circulating active TF and FXIa are associated with enhanced thrombin formation, with a minor effect of inflammatory mediators. Moreover, FXIa is also related to oxidative stress, indicating additional links between coagulation and free radical generation in stable angina.

Thrombin generation in severe sepsis

INTRODUCTION

Hemostasis and inflammation are two tightly interrelated systems in the host's response to infection. Thrombin generation in sepsis plays a crucial role in enhancing and modulation of inflammation. The present study aimed to investigate the course of thrombin generation in patients with severe sepsis, and its correlation with outcome.

MATERIALS AND METHODS

Thrombin generation was measured in platelet-poor plasma from 32 healthy controls and 75 patients with severe sepsis using the commercially available Calibrated Automated Thrombography. Samples were taken within 24 hours of the diagnosis of severe sepsis (t1) as well as on day 2 (t2), day 3 or 4 (t3) and between day 6 to 8 (t4), while this was done only once in healthy controls. The assay was run with and without the addition of thrombomodulin. Clinical data were also collected at the same time points.

RESULTS

Except for endogenous thrombin potential, there was significant difference between patients and controls regarding peak thrombin, lag time and time to thrombin peak. Twelve patients (16%) died in the ICU. There was no significant difference in endogenous thrombin potential between survivors and non-survivors of sepsis. Thrombin peak was higher in survivors than non-survivors at all time points, with a significant difference at t2 and t4. The lag time and time to thrombin peak were shorter in non-survivors than in survivors at t1 and t3.

CONCLUSIONS

While thrombin peak shows a positive correlation with survival, the lag phase and time to thrombin peak may be signs of impending DIC. The endogenous thrombin potential does not have any prognostic importance.

Plasma and cellular contributions to fibrin network formation, structure and stability

Growing evidence suggests that fibrin network structure and stability are important determinants of haemostasis and thrombosis, with alterations in fibrin structure implicated as a causative mechanism in various haemostatic and thrombotic disorders. In haemophilia, for example, deficiency of factor VIII or IX reduces the rate and peak of thrombin generation and produces coarse fibrin clots that show increased susceptibility to fibrinolysis. More recently, studies have shown significant effects of cellular activity and integrin composition on fibrin network and stability. Platelets support the formation of a dense, stable fibrin network via interactions between the alphaIIbbeta3 integrin and the fibrin network, whereas tissue factor-bearing cells regulate fibrin structure and stability predominantly via procoagulant activity. Highly procoagulant extravascular cells (e.g. fibroblasts and smooth muscle cells) support the formation of dense fibrin networks that resist fibrinolysis, whereas unstimulated intravascular cells (e.g. endothelial cells) produce coarser networks that are susceptible to fibrinolysis. Moreover, cellular contributions produce heterogeneous clots in which fibrin network density and stability decrease with increasing distance from the cell surface. Together, these findings suggest that specific plasma and cellular mechanisms link thrombin generation, clot stability and haemostatic or thrombotic outcome. Understanding these mechanisms may provide new therapeutic targets in the management of bleeding and thrombotic disorders.

Effects of inhalable particulate matter on blood coagulation

BACKGROUND

Particulate matter (PM) exposure has been linked to increased risk of cardiovascular disease, possibly resulting from hypercoagulability and thrombosis. Lung and systemic inflammation resulting from PM inhalation may activate blood coagulation, but mechanisms for PM-related hypercoagulability are still largely unknown.

OBJECTIVES

To identify coagulation mechanisms activated by PM in a population with well-characterized exposure.

METHODS

We measured prothrombin time (PT), activated partial thromboplastin time, endogenous thrombin potentials (ETPs) with/without exogenous triggers and with/without soluble thrombomodulin, tissue-type plasminogen activator (t-PA) antigen, D-dimer and C-reactive protein (CRP) in 37 workers in a steel production plant with well-characterized exposure to PM with aerodynamic diameter of < 1 mum (PM(1)) and coarse PM (PM(10) - PM(1)). Blood samples were collected from each subject on the first (baseline) and last (postexposure) day of a 4-day work week. We analyzed differences between baseline and postexposure levels using a paired Student's t-test. We fitted multivariate mixed-regression models to estimate the associations of interquartile range PM(1) and coarse PM exposure with parameter levels.

RESULTS

None of the parameters showed any significant changes from baseline in postexposure samples. However, exposure levels were associated with shorter PT (beta[PM(1)] = -0.33 s, P = 0.08; beta[PM(coarse)] = - 0.33 s, P = 0.01), and higher ETP without exogenous triggers and with thrombomodulin (beta[PM(1)] = + 99 nm min, P = 0.02; beta[PM(coarse)] = + 66 nm min, P = 0.05), t-PA (beta[PM(1)] = + 0.72 ng mL(-1), P = 0.01; beta[PM(coarse)] = + 0.88 ng mL(-1), P = 0.04), and CRP (beta[PM(1)] = + 0.59 mg L(-1), P = 0.03; beta[PM(coarse)] = + 0.48 mg L(-1), P = 0.01).

CONCLUSIONS

PM exposure did not show any short-term effect within the week of the study. The association of PM exposure with PT, ETP and CRP provides some evidence of long-term effects on inflammation and coagulation.

Effects of tissue factor, thrombomodulin and elevated clotting factor levels on thrombin generation in the calibrated automated thrombogram

Elevated procoagulant levels have been correlated with increased thrombin generation in vitro and with increased venous thromboembolism (VTE) risk in epidemiological studies. Thrombin generation tests are increasingly being employed as a high throughput method to provide a global measure of procoagulant activity in plasma samples. The objective of this study was to distinguish the effects of assay conditions [tissue factor (TF), thrombomodulin, platelets/lipids] and factor levels on thrombin generation parameters, and determine the conditions and parameters with the highest sensitivity and specificity for detecting elevated factor levels. Thrombin generation was measured using calibrated automated thrombography (CAT) in corn trypsin inhibitor (CTI)-treated platelet-free plasma (PFP) and platelet-rich plasma (PRP). Statistical analysis was performed using logarithms of observed values with analysis of variance that accounted for experiment and treatment. The relative sensitivity of lag time (LT), time to peak (TTP), peak height and endogenous thrombin potential (ETP) to elevated factors XI, IX, VIII, X, and prothrombin was as follows: PFP initiated with 1 pM TF > PFP initiated with 5 pM TF > PRP initiated with 1 pM TF. For all conditions, inclusion of thrombomodulin prolonged the LT and decreased the peak and ETP; however, addition of thrombomodulin did not increase the ability of CAT to detect elevated levels of individual procoagulant factors. In conclusion, CAT conditions differentially affected the sensitivity of thrombin generation to elevated factor levels. Monitoring the peak height and/or ETP following initiation of clotting in PFP with 1 pM TF was most likely to detect hypercoagulability due to increased procoagulant factor levels.

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

Thrombin is the central enzyme in the coagulation cascade. Estimation of an individual's potential to generate thrombin may correlate more closely with a hyper- or hypo-coagulable phenotype, compared to traditional coagulation tests. The possible correlation and recent technical advances in thrombin generation measurement has caused a significant interest in the method and the development of commercial assays. Several variations of the assay exist depending on the defect to be investigated. Fluorogenic thrombin generation assays have acceptable intra-laboratory variation but a higher inter-laboratory variation. Variation in preanalytical variables makes comparisons between studies difficult. Thrombin generation is highly variable between individuals and there are suggestions that this may allow individualized treatment based on global haemostatic response in patients with bleeding disorders or on anticoagulant therapy. In patients with thrombotic disorders it may be possible to identify those at higher risk of recurrent thrombosis. For both scenarios, however, data from large prospective studies are lacking or inconclusive and a good relationship between thrombin generation and phenotype remains to be established. Further standardization of the assay is needed before large multicentre studies can be conducted and until then thrombin generation in routine clinical practice is not yet a reality.

Influence of Factor V HR2 on Thrombin Generation and Clinical Manifestation in Rare Bleeding Disorders

In this study we investigated the influence of the presence of the factor V HR2 haplotype, defined by the factor V gene mutation H1299R (FV(HR2)), on thrombin generation. Measurements were performed in platelet-poor plasma of individuals with factor V(HR2) or factor V(Leiden) in comparison to a control group carrying none of these mutations. Coagulation was triggered by low concentrations of recombinant tissue factor in the presence of activated protein C. Thrombin generation was monitored by a fluorogenic substrate. The endogenous thrombin potential was calculated from the obtained curves. As a result we observed an increased thrombin generation both for individuals heterozygous and homozygous for FV(HR2). The level of endogenous thrombin potential is in the same range as in samples of patients heterozygous or homozygous for FV(Leiden). The results indicate that FV(HR2) plays a role as a risk factor for venous thrombosis in homozygous patients through an increased thrombin generation. The association between different clinical manifestations in individuals with FVII deficiency and endogenous thrombin potential and the presence of FV(HR2) was studied.