Comparison by sex between thrombin generation and fibrin network characteristics in a healthy population

Influence of Direct Oral Anticoagulant Levels and Thrombin Generation on Postoperative Bleeding [SONAR]: A Nested Case-Control Study

BACKGROUND

 A direct oral anticoagulant (DOAC) concentration threshold above which an impact on surgical hemostasis starts to occur is unknown. Thrombin generation assays (TGAs) provide a measure of the coagulation phenotype. This study aimed to determine whether preoperative TGA parameters are associated with postoperative bleeding, and whether this is partly due to residual DOAC levels.

MATERIALS AND METHODS

 We conducted a nested case-control study using samples from apixaban/rivaroxaban-treated patients with atrial fibrillation from the PAUSE (Perioperative Anticoagulation Use for Surgery Evaluation) perioperative study. Cases were participants with postoperative major or clinically relevant nonmajor bleeding; controls were participants without bleeding. DOAC levels were measured using a chromogenic anti-Xa assay (BIOPHEN DiXaI; rivaroxaban/apixaban calibrators). TGA parameters were measured using calibrated automated thrombography.Generalized linear mixed models and causal mediation analyses were used to evaluate the relationship between DOAC levels, TGA parameters, and bleeding.

RESULTS

 Forty eight cases were matched to 474 controls. Residual DOAC levels were higher in cases than controls (p¼0.03) and each TGA parameter was correlated with residual DOAC levels (p<0.05). A longer lag time (LT; odds ratio [OR]¼1.319 per minute [95% confidence interval [CI]: 1.077-1.617]) and time-to-peak (TTP; OR¼1.154 per minute [95% CI: 1.028-1.296]) were associated with an increased odds of bleeding; higher peak (OR¼0.994 per nM [95% CI: 0.989-0.998]) and mean velocity rate index (mVRI; OR¼0.986 per nM/min [95% CI: 0.976-0.996]) were associated with a lower odds of bleeding. The effect of apixaban/rivaroxaban levels on bleeding was mediated by altered TGA parameters (LT, TTP, peak, mVRI).

CONCLUSION

 These findings support a measurable effect from low residual DOAC levels on thrombin generation and suggest a causal contribution of both toward bleeding.

Does in vitro hemolysis affect measurements of plasma apixaban concentration by UPLC-MS and anti-Xa assay?

INTRODUCTION

Hemolytic interference may impact various laboratory tests, including coagulation analyses. Apixaban is the most commonly used direct oral anticoagulant in Norway, and there is lacking knowledge on how apixaban concentration measurements might be influenced by hemolysis. Moreover, hemolysis-induced alterations in apixaban levels could potentially impact the risk of bleeding in specific clinical scenarios. We wanted to study whether hemolysis would increase apixaban concentration and investigate the impact of hemolytic interference on apixaban concentration measurements.

METHODS

Blood samples from 20 apixaban-treated patients and 8 healthy controls were hemolyzed in vitro by a freeze method. The degree of hemolysis was measured with plasma free hemoglobin (PfHb) at baseline and two levels of hemolysis. Apixaban concentration was measured in plasma using both the chromogenic anti-Xa method and the ultraperformance liquid chromatography mass spectrometry (UPLC-MS). Thrombin generation assay was performed to assess coagulability.

RESULTS

UPLC-MS measurements showed a mean concentration change of -1.66% (±3.2%, p = 0.005) and anti-Xa assay showed a mean concentration change of 3.37% (±6.5%, p = 0.09) with increasing hemolysis. Thrombin generation lagtime decreased, and endogenous thrombin potential and peak thrombin increased with increasing hemolysis in both the control group and the apixaban group.

CONCLUSION

Apixaban concentration measurements by anti-Xa assay and UPLC-MS were not affected by hemolysis to a clinically relevant extent. Furthermore, hemolysis did not lead to hypocoagulability when assessed by thrombin generation.

Sex dimorphisms in coagulation: Implications in trauma-induced coagulopathy and trauma resuscitation

Trauma-induced coagulopathy (TIC) is one of the leading causes of preventable death in injured patients. Consequently, it is imperative to understand the mechanisms underlying TIC and how to mitigate this mortality. An opportunity for advancement stems from the awareness that coagulation demonstrates a strong sex-dependent effect. Females exhibit a relative hypercoagulability compared to males, which persists after injury and confers improved outcomes. The mechanisms underlying sex dimorphisms in coagulation and its protective effect after injury have yet to be elucidated. This review explores sex dimorphisms in enzymatic hemostasis, fibrinogen, platelets, and fibrinolysis, with implications for resuscitation of patients with TIC.

Exercise and hypoxia-induced hypercoagulability is counterbalanced in women in part by decreased platelet reactivity

Hypoxia plays an important role in several pathologies, e.g. chronic obstructive pulmonary disease and obstructive sleep apnea syndrome, and is linked to an increased thrombosis risk. Furthermore, oxygen deprivation is associated with hypercoagulability. In this study, we investigated the effect of gender and exercise on the coagulation potential under hypoxic conditions at high altitude by assessing thrombin generation (TG) and platelet activation. Hereto, ten healthy volunteers were included (50 % male, median age of 27.5 years). The measurements were conducted first at sea level and then twice at high altitude (3883 m), first after a passive ascent by cable car and second after an active ascent by a mountain hike. As expected, both the passive and active ascent resulted in a decreased oxygen saturation and an increased heart rate at high altitude. Acute mountain sickness symptoms were observed independently of the ascent method. After the active ascent, platelet, white blood cell and granulocyte count were increased, and lymphocytes were decreased, without a gender-related difference. FVIII and von Willebrand factor were significantly increased after the active ascent for both men and women. Platelet activation was reduced and delayed under hypobaric conditions, especially in women. TG analysis showed a prothrombotic trend at high altitude, especially after the active ascent. Women had a hypercoagulable phenotype, compared to men at all 3 timepoints, indicated by a higher peak height and endogenous thrombin potential (ETP), and shorter lag time and time-to-peak. In addition, ETP and peak inhibition by thrombomodulin was lower in women after the active ascent, compared to men. Interestingly, data normalisation for subject baseline values indicated an opposing effect of altitude-induced hypoxia on α2-macroglobulin levels and TG lag time between men and women, decreasing in men and increasing in women. We conclude that hypoxia increases TG, as well as FVIII and VWF levels in combination with exercise. In contrast, platelets lose their responsiveness at high altitude, which is most pronounced after heavy exercise. Women had a more pronounced prothrombotic phenotype compared to men, which we theorize is counterbalanced under hypobaric conditions by decreased platelet activation.

The thrombin generation capability of the Chacma baboon (Papio ursinus): implications for haemostatic disease models

Baboon models are often used to investigate haemostatic diseases, such as acquired thrombotic thrombocytopenic purpura or bacterial sepsis-induced disseminated intravascular coagulation, and their potential treatment with novel drugs. Thrombin generation is vital for these models, and an important potential therapeutic target. We investigated the thrombin generation profile of the Chacma baboon (Papio ursinus - a common pre-clinical model) including the effects of sex and ABO blood group. Thrombin generation curves, lag times, peak heights, times-to-peak, velocity indexes and Endogenous Thrombin Potentials (ETPs) of 40 adult Chacma baboons were assessed and compared with normal human plasma, using a low concentration of tissue factor (1 pM) and phospholipids. Reference intervals were calculated, and results compared between O and non-O ABO blood groups, and between males and females. Lag times of all baboons fell within the human reference interval. Most animals (n = 32; 80%) had times-to-peak above, and velocity indexes and peak heights markedly below (n = 27; 68%) the human range. However, 97.5% of baboons had an ETP above the human reference interval, indicating greater overall thrombin generation. ABO blood group had no effect, but males (n = 14; 35%) had less potent thrombin generation than females (n = 26; 65%), with significantly longer lag times (p = 0.0475), lower peak thrombin concentrations (p = 0.0203), and lower ETPs (p = 0.0238). Chacma baboons have greater overall endogenous thrombin generation potentials than humans, which is even more prominent in females. This should be considered when designing future baboon model experiments involving the haemostatic system, or when evaluating novel therapies in these animals.

Thrombin generation assay: the present and the future

The need for a more precise test that replicates the in vivo hemostatic conditions is increasingly being recognized. Up to now, the thrombin generation assay (TGA) has become the most reliable approach to evaluate the status of coagulation activation. The clinical potential for the TGA is most promising in the prediction of venous thromboembolism recurrence. However, there is currently an urgent need for a standardized global test that can reliably detect, predict and monitor coagulation disorders in both clinical and experimental studies. We have recently modified the TGA to analyze not only tissue factor-driven coagulation, but the intrinsic coagulation pathway as well. In the present review, we discuss different TG tests, emphasizing the requirement for a better understanding of the evaluation of distinct coagulation pathways using this technique, as well as the standardization and clinical validation.

Sex-dependent balance between thrombin and plasmin generation in the presence of thrombomodulin

BACKGROUND

Assessing simultaneous generation of thrombin (TG) and plasmin (PG) is an approach to evaluate the balance between coagulation and fibrinolysis with sensitivity to predict endogenous thrombin and plasmin generation. The addition of thrombomodulin (TM), provides the essential component for thrombin activation of protein C and thrombin-activatable fibrinolysis inhibitor. However, the influence of sex on the balance between TG and PG with and without TM addition has not been investigated to date.

OBJECTIVES

To investigate the possible sex-based differences in TG and PG in the presence and absence of TM.

METHODS

Simultaneous TG and PG were measured in plasma samples obtained from 17 males and 17 females upon tissue factor and tissue plasminogen activator addition. Thrombin- and plasmin-specific fluorogenic substrates Z-Gly-Gly-Arg-AMC and Boc-Glu-Lys-Lys-AMC were used in the study. Thrombin and plasmin peak height (TPH and PPH) and production rate (TPR and PPR) values were determined. To evaluate the balance between TG and PG, the ratios between TPH and PPH (TPH/PPH) and TPR and PPR (TPR/PPR) were calculated.

RESULTS AND CONCLUSIONS

TPH between males and females demonstrated significant difference regardless of TM addition. TPR demonstrated differences between males and females only upon TM addition, while PG parameters was not dependent on the sex of the donor. TM significantly lowered TPH/PPH in males, and enhanced TPR/PPR in females. Thus, TPH/PPH and TPR/PPR significantly differed between men and women. Our results indicate that TM may act differently in males and females by shifting the underlying TG/PG balance to fibrinolysis in males and to coagulation in females.

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.

Gender-specific differences in haemostatic parameters and their influence on blood loss in bimaxillary surgery

Objective

The objectives of this prospective cohort study were to establish gender-related differences in blood loss and haemostatic profiles associated with bimaxillary surgery. In addition, we aimed to identify if any gender differences could be established which might help predict blood loss volume.

Materials and methods

Fifty-four patients (22 males; 32 females) undergoing bimaxillary surgery for skeletal dentofacial deformities were eligible for inclusion. Blood samples were taken 1 day preoperatively and 48 h postoperatively for detailed gender-specific coagulation analysis incorporating global coagulation assays (endogenous thrombin potential) and specific coagulation parameters. Blood loss was measured at two different time points: (1) the end of surgery, visible intraoperative blood loss (IOB) using ‘subtraction method’; and (2) 48 h postoperatively perioperative bleeding volume (CBL-48 h) using ‘haemoglobin-balance method’ and Nadler’s formula. Correlation and regression analyses were performed to identify relevant parameters affecting the amount of blood loss.

Results

Significant differences in IOB and CBL-48 h were observed (p < 0.001). Men had higher IOB versus women, lacking statistical significance (p = 0.056). In contrast, men had significantly higher CLB-48 h (p = 0.019). Reduced CBL-48 h was shown to be most closely associated with the level of Antithrombin-III being decreased in females.

Conclusions

Male gender is associated with higher IOB and CBL-48 compared with females. Gender does not affect IOB regarding haemostatic profile but does correlate strongly with procedure length. Conversely, CBL-48 is closely associated with gender-specific imbalances in the anticoagulant system.

Clinical relevance

Knowledge of gender-related differences will help clinicians establish predictive factors regarding excessive blood loss in orthognathic surgery and identify at-risk patients.

Thrombin generation is associated with ischemic stroke at a young age

INTRODUCTION

Understanding the underlying mechanisms in ischemic stroke (IS) in young adults remains challenging. Thrombin activates processes that contribute to the development and progression of arterial diseases. We investigated the association between thrombin generation (TG) and a first IS or transient ischemic attack (TIA) in young adults.

METHODS

In this case-control study, we included consecutive patients (≤45 years in men, ≤55 years in women) with a first IS or TIA (n = 160) and healthy controls (n = 160). TG was determined with the calibrated automated thrombogram (CAT) assay. Logistic regression was used to analyze the association between TG and IS. Men and women were analyzed separately.

RESULTS

TG started earlier, reached its peak earlier and was also terminated earlier in patients than in healthy controls. Peak height (PH) was higher in patients than in controls, 227 nM (25th-75th percentile 145-326) versus 179 nM (110-294), p = 0.02. The endogenous thrombin potential (ETP) was not different in patients and controls, 1530 nM·min (1089-2045) versus 1454 nM·min (1011-2139), p = 0.52. Lag time (LT) (Odds Ratio (OR) 0.91 (95% confidence interval (CI) 0.83-0.99)), time to peak (TTP) (OR 0.91, 95% CI 0.84-0.97) and time to tail (TTT) (OR 0.92, 95% CI 0.88-0.97) were associated with a first IS and TIA. In men LT, TTP and TTT were associated with IS, but not in women.

CONCLUSIONS

We found that TG parameters are associated with a first IS in young patients. Further prospective studies are warranted to elucidate the role of TG in IS.

Exploring the utility of a novel point-of-care whole blood thrombin generation assay following trauma: A pilot study

INTRODUCTION

Plasma thrombin generation kinetics as measured by the calibrated automated thrombogram (CAT) assay is a predictor of symptomatic venous thromboembolism after trauma. We hypothesized that data from a new prototype assay for measurement of thrombin generation kinetics in fresh whole blood (near patient testing of thrombin generation), will correlate with the standard CAT assay in the same patients, making it a potential tool in the future care of trauma patients.

METHODS

Patients were enrolled from June 2018 to February 2020. Within 12 hours of injury, blood samples were collected simultaneously for both assays. Variables compared and correlated between assays were lag time, peak height, time to peak, and endogenous thrombin potential. Data are presented as median with interquartile range (IQR). Spearman and Pearson correlations were estimated and tested between both assays; a P value of <0.05 was considered to be significant.

RESULTS

A total of 64 trauma patients had samples analyzed: injury severity score = 17 (IQR), 10-26], hospital length of stay = 7.5 (IQR), 2-18) days, age = 52 (IQR, 35-63) years, 71.9% male, and 42.2% of patients received a transfusion within 24 hours of injury. Thrombin generation parameters between plasma and whole blood were compared and found that all parameters of the two assays correlate in trauma patients.

CONCLUSION

In this pilot study, we have found that a novel point-of-care whole blood thrombin generation assay yields results with modest but statistically significant correlations to those of a standard plasma thrombin generation assay. This finding supports studying this device in a larger, adequately powered study.

Thrombin generation in cardiovascular disease and mortality - results from the Gutenberg Health Study

Thrombin generation may be a potential tool to improve risk stratification for cardiovascular diseases. This study aims to explore the relation between thrombin generation and cardiovascular risk factors, cardiovascular diseases, and total mortality. For this study, N=5000 subjects from the population-based Gutenberg Health Study were analysed in a highly standardized setting. Thrombin generation was assessed by the Calibrated Automated Thrombogram method at 1 and 5 pM tissue factors trigger in platelet poor plasma. Lag time, endogenous thrombin potential, and peak height were derived from the thrombin generation curve. Sex-specific multivariable linear regression analysis adjusted for age, cardiovascular risk factors, cardiovascular diseases and therapy, was used to assess clinical determinants of thrombin generation. Cox regression models adjusted for age, sex, cardiovascular risk factors and vitamin K antagonists investigated the association between thrombin generation parameters and total mortality. Lag time was positively associated with obesity and dyslipidaemia for both sexes (p<0.0001). Obesity was also positively associated with endogenous thrombin potential in both sexes (p<0.0001) and peak height in males (1 pM tissue factor, p=0.0048) and females (p<0.0001). Cox regression models showed an increased mortality in individuals with lag time (1 pM tissue factor, hazard ratio=1.46, [95% CI: 1.07; 2.00], p=0.018) and endogenous thrombin potential (5 pM tissue factor, hazard ratio = 1.50, [1.06; 2.13], p=0.023) above the 95th percentile of the reference group, independent of the cardiovascular risk profile. This large-scale study demonstrates traditional cardiovascular risk factors, particularly obesity, as relevant determinants of thrombin generation. Lag time and endogenous thrombin potential were found as potentially relevant predictors of increased total mortality, which deserves further investigation.

Gender related issues in thrombosis and hemostasis

INTRODUCTION

Many aspects of hemostasis, both primary and secondary, as well as fibrinolysis display sex differences. From a clinical viewpoint, certain differential phenotypic presentations clearly arise within various disorders of thrombosis and hemostasis. Areas covered: The present mini-review summarizes selected clinical entities where sex differences are reflected in both frequency and clinical presentation of hemostasis disorders. Sex differences are discussed within the settings of cardiovascular disease, including coronary artery disease and ischemic stroke, venous thromboembolism and inherited bleeding disorders. Moreover, pregnancy and labor present particular challenges in terms of increased thromboembolic and bleeding risk, and this is also summarized. Expert commentary: Available knowledge on sex differences in risk factors and clinical presentation of disorders within thrombosis and hemostasis is increasing. However, more evidence is needed to further clarify different risk factors and treatment effect in men and women, both as regards to cardiovascular disease and venous thromboembolism. This should facilitate improved gender guided risk stratification, and prevention and treatment of these diseases. Finally, risk assessment during pregnancy remains a challenge; this applies both to thromboembolic risk assessment during normal pregnancy and special care of women with inherited bleeding disorders during labor.

Anticoagulant properties of enoxaparin 400 IU/mL-40 % ethanol catheter lock solution

Unfractionated heparin (UFH) is the most widely used interdialytic lock solution but has no anti-infectious properties. Ethanol at a content ≥40 %v/v eradicates experimental biofilm but has no anticoagulant properties. In contrast to UFH, enoxaparin (Enox) can be combined with 40 % ethanol without precipitation. Enoxaparin 400 UI/mL–40 % ethanol (Enox/Eth) has antibiofilm properties and therefore has promise as an alternative lock solution. This study assessed the anticoagulant properties of Enox/Eth. Enox and Enox/Eth were diluted in whole blood at a final Enox concentration of 0.5, 1 (N = 6 samples), 1.5 (N = 4) and 2 (N = 6) IU/mL. Anti-Xa activity was determined by chromogenic assay and the inhibition of endogenous thrombin potential (ETP) by thrombinography. Quantitative data were compared by the Mann-Withney U test. For Enox concentrations of 0.5, 1, 1.5 and 2 UI/mL in whole blood samples, the mean ± SD values of the anti-Xa activity were 0.68 ± 0.09, 1.26 ± 0.14, 1.73 ± 0.30, 2.35 ± 0.32 UI/mL for Enox/Eth and 0.94 ± 0.15, 1.80 ± 0.22, 2.74 ± 0.23, 3.54 ± 0.44 UI/mL for Enox (P = 0.03, P = 0.03, P = 0.13, P = 0.03); and of the percentage of ETP inhibition was 17.36 ± 9.65, 30.27 ± 17.06, 36.5 ± 17.06, 57.82 ± 15.42 for Enox/Eth, and 42.96 ± 15.68, 68.93 ± 10.01, 83.5 ± 8.81, 91.19 ± 4.67 for Enox (P = 0.03, P = 0.03, P = 0.13, P = 0.03), respectively. The median and IQR values of Enox concentration inhibiting 50 % of ETP (IC50 ETP) were 1.8 [1.1–2.4] IU/mL for Enox/Eth and 0.7 [0.3–0.9] IU/mL for Enox, P = 0.03. Enox/Eth has strong anticoagulant activity, albeit lower than that of Enox, but with an extremely low IC50 ETP compared to the Enox concentration of non-diluted Enox/Eth.