Low paediatric thrombin generation is caused by an attenuation of prothrombin conversion

Prothrombin conversion and thrombin decay in patients with cirrhosis-role of prothrombin and antithrombin deficiencies

BACKGROUND

Thrombin generation (TG) in the presence of thrombomodulin (TG-TM) in the plasma of patients with cirrhosis (PWC) is tilted toward a hypercoagulable phenotype. Low protein C and elevated factor VIII levels play a role, but other determinants, such as the prothrombin/antithrombin pair, must also be studied.

OBJECTIVES

The objectives were (i) to quantitatively assess the subprocesses (prothrombin conversion and thrombin decay) and (ii) to understand the underlying mechanism by studying TG dynamics after prothrombin and antithrombin plasma level correction in PWC.

METHODS

We studied TG-TM in plasma samples of 36 healthy controls (HCs) and 41 PWC with prothrombin and antithrombin levels of <70% and after their correction. We initiated coagulation with an intermediate picomolar concentration of tissue factor. We determined the overall thrombin potential, prothrombin conversion, and thrombin decay.

RESULTS

TG-TM was increased in PWC compared with HC due to impaired thrombin inhibition. Indeed, thrombin decay capacity (min-1) decreased from 0.37 (0.35-0.40) in HC to 0.33 (0.30-0.37) in the Child-Turcotte-Pugh A (CTP-A; P = .09), 0.27 (0.26-0.30) in the CTP-B (P < .001), and 0.20 (0.19-0.20) in the CTP-C (P < .001) group. Concomitant correction of prothrombin and antithrombin increased endogenous thrombin potential with prothrombin conversion surpassing thrombin decay. By contrast, when we corrected only antithrombin, TG-TM was normalized and even consistent with a hypocoagulable phenotype in the CTP-C group.

CONCLUSION

Our results highlight that in PWC, hypercoagulability (evidenced in the presence of TM) is due to impaired thrombin decay, whereas low prothrombin levels do not translate into decreased prothrombin conversion, likely due to altered TM-activated protein C negative feedback.

High alpha-2-macroglobulin levels are a risk factor for cardiovascular disease events: A Moli-sani cohort study

BACKGROUND

α2-macroglobulin (α2M) is a versatile endopeptidase inhibitor that plays a role in cell growth, inflammation and coagulation. α2M is an inhibitor of key coagulation enzyme thrombin. Hypercoagulability due to an excess of thrombin production can cause thrombotic events. Therefore, we investigated the association of α2M levels and cardiovascular events in a subset of the general Italian population.

METHODS

We determined α2M levels in the baseline samples of a prospective cohort (n = 19,688; age: 55 ± 12 years; 47.8 % men) of the Moli-sani study and investigated the association with the cardiovascular events (n = 432, 2.2 %) in the median follow-up period of 4.3 years. Hazard ratios (HR) with 95 % confidence intervals (CI) were calculated by multivariable Cox regression and adjusted for a large panel of confounding factors.

RESULTS

α2M levels above the 90th percentile were significantly associated with cardiovascular disease (CVD) events after full adjustment for age, sex, current smoking, BMI, oral contraceptive use, cardiovascular diseases, hypertension, hypercholesterolemia, diabetes and history of cancer (HR: 1.36; CI: 1.06-1.74). Moreover, high α2M was associated with coronary heart disease (CHD; HR: 1.47; CI: 1.12-1.91), but not stroke. Stratification for CVD at baseline showed that high α2M levels are associated with CHD events in subjects without CVD at baseline (HR: 1.40; CI: 1.00-1.95) and subjects with CVD at baseline (HR: 1.58; CI: 1.02-2.44).

CONCLUSION

We show in a prospective cohort that high levels of α2M could be a risk factor for cardiovascular events, especially coronary heart disease events.

Antiplatelet Effect of Melatonin through Breastfeeding: A Pediatric Case Report

We present a pediatric case of the antiplatelet effect of melatonin taken through breast milk in an 18-month-old child. The child was referred to our hematology outpatient clinic because of bleeding episodes that she presented since birth. Blood tests excluded the presence of blood coagulation diseases. The family history was negative for bleeding disorders. The child did not consume any drugs, food supplements, herbal teas or infusions. We performed an aggregation platelet test, which showed a reduced platelet aggregation. Shortly before, the baby had been breastfed. We speculated that breast milk could interfere with the result of the test; therefore, we decided to repeat the test in a fasting state. This time the test showed a normal platelet aggregation time. We learned that the child's mother was taking a mixture of valerian and melatonin. Thus, we decided to suspend maternal intake of melatonin and perform a new platelet aggregation test after three months. The test results were negative. After the suspension of melatonin, the patient did not present further bleeding events. In this case, melatonin, through the inhibition of platelet aggregation, had an important role on the hemostatic system of the child. Melatonin is considered as a dietary supplement and is mostly available as an alternative medicine without formal prescription and dosage regulation. It is important, especially during breastfeeding, to investigate personal and medication history, including also homeopathic remedies or dietary supplements.

Plasma thrombin generation kinetics vary by injury pattern and resuscitation characteristics in pediatric and young adult trauma patients

BACKGROUND

Thrombin generation kinetics are not well studied in children. This study aimed to assess how thrombin generation kinetics vary in pediatric and young adult (YA) trauma patients by clinical characteristics and injury pattern.

METHODS

Prospective cohort study where plasma samples were obtained from pediatric (ages 0-17 years) and YA (ages 18-21 years) trauma patients upon emergency department arrival. Thrombin generation (calibrated automated thrombogram [CAT]) was quantified as lag time (LT, minutes), peak height (PH, nM), time to peak (ttPeak, minutes), and endogenous thrombin potential (ETP, nM × minute). Results are expressed as median and quartiles [Q1, Q3] and compared using Wilcoxon rank sum testing with p < 0.05 considered significant.

RESULTS

We enrolled 47 pediatric (median age, 15 [14, 17] years, 78% male, 87% blunt, median Injury Severity Score, 12) and 49 YA (median age 20 [18, 21] years, 67% male, 84% blunt, median Injury Severity Score, 12) patients. Pediatric and YA patients had similar rates of operative intervention (51% vs. 57%), transfusion (25% vs. 20%), and traumatic brain injury (TBI) (53% vs. 49%). Pediatric patients who required an operation had accelerated initiation of thrombin generation, with shorter LT than those who did not (2.58 [2.33, 2.67]; 2.92 [2.54, 3.00], p = 0.034). Shorter LT (2.41 [2.22, 2.67]; 2.67 [2.53, 3.00]) and ttPeak (4.50 [4.23, 4.73]; 5.22 [4.69, 5.75], both p < 0.01) were noted in pediatric patients who required transfusion as compared with those who did not. The YA patients requiring transfusion had shorter LT (2.33 [2.19, 2.74]; 2.83 [2.67, 3.27]) and ttPeak (4.48 [4.33, 5.65]; 5.33 [4.85, 6.28] both p < 0.04) than those who were not transfused. Young adults with TBI had greater ETP than those without (1509 [1356, 1671]; 1284 [1154, 1471], p = 0.032).

CONCLUSION

Thrombin generation kinetics in pediatric trauma patients prior to intervention vary with need for operation and transfusion, while thrombin generation kinetics in young adult patients are influenced by TBI and need for operation or transfusion. This is a promising tool for assessing coagulopathy in young trauma patients.

LEVEL OF EVIDENCE

Prognostic and Epidemiological; Level III.

Children and Snakebite: Snake Venom Effects on Adult and Paediatric Plasma

Snakebite is a globally neglected tropical disease, with coagulation disturbances being the primary pathology of many deadly snake venoms. Age-related differences in human plasma have been abundantly reported, yet the effect that these differences pose regarding snakebite is largely unknown. We tested for differences in coagulotoxic effects (via clotting time) of multiple snake venoms upon healthy human adult (18+) and paediatric (median 3.3 years old) plasma in vivo and compared these effects to the time it takes the plasmas to clot without the addition of venom (the spontaneous clotting time). We tested venoms from 15 medically significant snake species (from 13 genera) from around the world with various mechanisms of coagulotoxic actions, across the three broad categories of procoagulant, pseudo-procoagulant, and anticoagulant, to identify any differences between the two plasmas in their relative pathophysiological vulnerability to snakebite. One procoagulant venom (Daboia russelii, Russell's Viper) produced significantly greater potency on paediatric plasma compared with adult plasma. In contrast, the two anticoagulant venoms (Pseudechis australis, Mulga Snake; and Bitis cornuta, Many-horned Adder) were significantly more potent on adult plasma. All other procoagulant venoms and all pseudo-procoagulant venoms displayed similar potency across both plasmas. Our preliminary results may inform future studies on the effect of snake venoms upon plasmas from different age demographics and hope to reduce the burden of snakebite upon society.

Plasma thrombin generation kinetics in trauma patients across the age spectrum

Background

Injured patients have early changes to normal coagulation that can impact long term risk for thrombotic complications. There is little known about how age impacts biomarkers of coagulation after traumatic injury. In this pilot study, we aimed to characterize thrombin generation kinetics, a known predictor of venous thromboembolism, in trauma patients across the age spectrum.

Methods

Citrated plasma samples were collected from 174 trauma patients (3-94 years old). Thrombin generation kinetics were measured using calibrated automated thrombogram (CAT) and expressed as lag time (LT - minutes) and time to peak (ttPeak - minutes). Kruskal-Wallis, Spearman correlation, and multivariable regression analysis were carried out. Data in median and quartiles [Q1, Q3]. P < 0.05 significant.

Results

Pediatric patients (n = 14) had shortest LT and ttPeak compared to adult and geriatric (n = 43), who had longest (LT: 2.67 [2.48, 3.00] vs. 2.93 [2.56, 3.48] vs. 3.15 [2.74, 3.67], p = 0.029; ttPeak: 4.98 [4.67, 5.67] vs. 5.53 [5.00, 6.56] vs. 5.94 [5.52, 6.91], p = 0.011). LT and ttPeak correlated with age (Spearman 0.285 and 0.305, both p < 0.001). Clinical factors, specifically, age, injury severity score, and transfusion status were associated with LT and ttPeak in multivariable models.

Conclusions

Trauma patients exhibit prolonged initiation and time to peak thrombin generation with age. Further studies are needed to determine the age-specific role of thrombin generation kinetics in thrombotic complications after trauma.

Neonatal Platelets: Lower G12/13 Expression Contributes to Reduced Secretion of Dense Granules

Despite fully functional primary hemostasis, platelets of healthy neonates exhibit hypoaggregability and secretion defects, which may be adaptations to specific requirements in this developmental stage. The etiologies for reduced signal transduction vary with the type of agonist. The discovered peculiarities are lower receptor densities, reduced calcium mobilization, and functional impairments of G proteins. Reduced secretion of dense granules has been attributed to lower numbers of granules. Signaling studies with adult platelets have shown a regulating effect of the G_12/13 signaling pathway on dense granule secretion via RhoA. We comparatively analyzed secretion profiles using flow cytometry and expression levels of G_q, G_i, and G_12/13 using Western blot analysis in platelets from cord blood and adults. Furthermore, we evaluated Rho activation after in vitro platelet stimulation with thrombin using a pulldown assay. We observed a markedly reduced expression of the dense granule marker CD63 on neonatal platelets after thrombin stimulation. G_α12/13 expression was significantly decreased in neonatal platelets and correlated with lower Rho activation after thrombin stimulation. We conclude that lower expression of G_12/13 in neonatal platelets results in attenuated activation of Rho and may contribute to reduced secretion of dense granules after exposure to thrombin.

Semi-automated thrombin dynamics applying the ST Genesia thrombin generation assay

Background

The haemostatic balance is an equilibrium of pro- and anticoagulant factors that work synergistically to prevent bleeding and thrombosis. As thrombin is the central enzyme in the coagulation pathway, it is desirable to measure thrombin generation (TG) in order to detect possible bleeding or thrombotic phenotypes, as well as to investigate the capacity of drugs affecting the formation of thrombin. By investigating the underlying processes of TG (i.e., prothrombin conversion and inactivation), additional information is collected about the dynamics of thrombin formation.

Objectives

To obtain reference values for thrombin dynamics (TD) analysis in 112 healthy donors using an automated system for TG.

Methods

TG was measured on the ST Genesia, fibrinogen on the Start, anti-thrombin (AT) on the STA R Max and α₂Macroglobulin (α₂M) with an in-house chromogenic assay.

Results

TG was measured using STG-BleedScreen, STG-ThromboScreen and STG-DrugScreen. The TG data was used as an input for TD analysis, in combination with plasma levels of AT, α₂M and fibrinogen that were 113% (108-118%), 2.6 μM (2.2 μM-3.1 μM) and 2.9 g/L (2.6-3.2 g/L), respectively. The maximum rate of the prothrombinase complex (PCmax) and the total amount of prothrombin converted (PCtot) increased with increasing tissue factor (TF) concentration. PC_tot increased from 902 to 988 nM, whereas PC_max increased from 172 to 508 nM/min. Thrombin (T)-AT and T-α₂M complexes also increased with increasing TF concentration (i.e., from 860 to 955 nM and from 28 to 33 nm, respectively). PC_tot, T-AT and T-α₂M complex formation were strongly inhibited by addition of thrombomodulin (-44%, -43%, and -48%, respectively), whereas PC_max was affected less (-24%). PC_tot, PC_max, T-AT, and T-α₂M were higher in women using oral contraceptives (OC) compared to men/women without OC, and inhibition by thrombomodulin was also significantly less in women on OC (p < 0.05).

Conclusions

TG measured on the ST Genesia can be used as an input for TD analysis. The data obtained can be used as reference values for future clinical studies as the balance between prothrombin conversion and thrombin inactivation has shown to be useful in several clinical settings.

Age-Dependent Heterogeneity in the Efficacy of Prophylaxis With Enoxaparin Against Catheter-Associated Thrombosis in Critically Ill Children: A Post Hoc Analysis of a Bayesian Phase 2b Randomized Clinical Trial

OBJECTIVES

We explored the age-dependent heterogeneity in the efficacy of prophylaxis with enoxaparin against central venous catheter-associated deep venous thrombosis in critically ill children.

DESIGN

Post hoc analysis of a Bayesian phase 2b randomized clinical trial.

SETTING

Seven PICUs.

PATIENTS

Children less than 18 years old with newly inserted central venous catheter.

INTERVENTIONS

Enoxaparin started less than 24 hours after insertion of central venous catheter and adjusted to anti-Xa level of 0.2-0.5 international units/mL versus usual care.

MEASUREMENTS AND MAIN RESULTS

Of 51 children randomized, 24 were infants less than 1 year old. Risk ratios of central venous catheter-associated deep venous thrombosis with prophylaxis with enoxaparin were 0.98 (95% credible interval, 0.37-2.44) in infants and 0.24 (95% credible interval, 0.04-0.82) in older children greater than or equal to 1 year old. Infants and older children achieved anti-Xa level greater than or equal to 0.2 international units/mL at comparable times. While central venous catheter was in situ, endogenous thrombin potential, a measure of thrombin generation, was 223.21 nM.min (95% CI, 8.78-437.64 nM.min) lower in infants. Factor VIII activity, a driver of thrombin generation, was also lower in infants by 45.1% (95% CI, 15.7-74.4%). Median minimum platelet count while central venous catheter was in situ was higher in infants by 39 × 103/mm3 (interquartile range, 17-61 × 103/mm3). Central venous catheter:vein ratio was not statistically different. Prophylaxis with enoxaparin was less efficacious against central venous catheter-associated deep venous thrombosis at lower factor VIII activity and at higher platelet count.

CONCLUSIONS

The relatively lesser contribution of thrombin generation on central venous catheter-associated thrombus formation in critically ill infants potentially explains the age-dependent heterogeneity in the efficacy of prophylaxis with enoxaparin.

Deciphering the coagulation profile through the dynamics of thrombin activity

Thrombosis has proven to be extremely difficult to predict. Measuring the generation of thrombin is a very sensitive method to detect changes in the hemostatic system. We developed a method based on the generation of thrombin to further fingerprint hemostasis, which we have named thrombin dynamics. Via this method we are able to exactly measure the prothrombin conversion and thrombin inactivation, and any change in the coagulation cascade will be reflected in these two processes. In the current study we analyzed the importance of the members of the prothrombin complex on the dynamics of thrombin activation and inactivation. We show that prothrombin conversion is predominantly influenced by factor X and antithrombin, which will provide essential insights in complex thrombosis-related diseases, such as liver cirrhosis and kidney failure.

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.

Elevated thrombin generation in patients with congenital disorder of glycosylation and combined coagulation factor deficiencies

BACKGROUND

Congenital disorders of glycosylation are rare inherited diseases affecting many different proteins. The lack of glycosylation notably affects the hemostatic system and leads to deficiencies of both procoagulant and anticoagulant factors.

OBJECTIVE

To assess the hemostatic balance in patients with multiple coagulation disorders by using a thrombin generation assay.

METHOD

We performed conventional coagulation assays and a thrombin generation assay on samples from patients with congenital disorder of glycosylation. The thrombin generation assay was performed before and after activation of the protein C system by the addition of soluble thrombomodulin.

RESULTS

A total of 35 patients were included: 71% and 57% had low antithrombin and factor XI levels, respectively. Protein C and protein S levels were abnormally low in 29% and 26% of the patients, respectively, whereas only 11% displayed low factor IX levels. Under baseline conditions, the thrombin generation assay revealed a significantly higher endogenous thrombin potential and thrombin peak in patients, relative to controls. After spiking with thrombomodulin, we observed impaired involvement of the protein C system. Hence, 54% of patients displayed a hypercoagulant phenotype in vitro. All the patients with a history of stroke-like episodes or thrombosis displayed this hypercoagulant phenotype.

CONCLUSION

A thrombin generation assay revealed a hypercoagulant in vitro phenotype under baseline condition; this was accentuated by impaired involvement of the protein C system. This procoagulant phenotype may thus reflect the risk of severe vascular complications. Further research will have to determine whether the thrombin generation assay is predictive of vascular events.

In vitro assessment of edoxaban anticoagulant effect in pediatric plasma

INTRODUCTION

Anticoagulant therapy in pediatric patients remains an issue and safer therapies, such as direct oral anticoagulants could overcome the limitations of conventional anticoagulant treatments in this population. Edoxaban, a factor Xa inhibitor, is used for the prevention and treatment of venous thromboembolism. Due to its pharmacokinetic characteristics, edoxaban is a promising candidate molecule for children. This study compared edoxaban in vitro effect in children and adults.

MATERIALS AND METHODS

Blood samples were prospectively collected from 87 adults and 97 children (n = 12: <2 year-old; n = 8: 2-4 year-old; n = 9: 5-7 year-old; n = 14: 8-9 year-old; n = 10: 10-13 year-old; n = 15: 14-15 year-old; and n = 29: 16-18 year-old). Plasma samples were supplemented in vitro with edoxaban to a final concentration of 50, 150 or 300 ng/mL, and then edoxaban effect on prothrombin time (PT), activated partial thromboplastin time (aPTT), fibrinogen (Clauss assay), specific anti-factor Xa activity and thrombin generation assay (TGA) (with 5pM tissue factor and 4 nM phospholipids) was evaluated.

RESULTS

PT, aPTT, and specific anti-Xa activity exhibited similar dose-dependent responses to edoxaban in the different age groups. The reduction of thrombin peak, the most edoxaban-sensitive TGA parameter, was similar in adults and children, but for the youngest group (<2 year-old) where the peak value reduction (median [Q1-Q3]) was higher than in adults (51% [44-59] versus 40% [32-46], p < 0.01; 74% [63-80] versus 65% [58-70], p < 0.05; and 84% [73-88] versus 76% [70-80], p < 0.05 for 50, 150 and 300 ng/mL edoxaban, respectively).

CONCLUSIONS

Edoxaban in vitro effect are comparable in children and adults except in the <2-year-old group.

Mathematical modelling indicates that lower activity of the haemostatic system in neonates is primarily due to lower prothrombin concentration

Haemostasis is governed by a highly complex system of interacting proteins. Due to the central role of thrombin, thrombin generation and specifically the thrombin generation curve (TGC) is commonly used as an indicator of haemostatic activity. Functional characteristics of the haemostatic system in neonates and children are significantly different compared with adults; at the same time plasma levels of haemostatic proteins vary considerably with age. However, relating one to the other has been difficult, both due to significant inter-individual differences for individuals of similar age and the complexity of the biochemical reactions underlying haemostasis. Mathematical modelling has been very successful at representing the biochemistry of blood clotting. In this study we address the challenge of large inter-individual variability by parameterising the Hockin-Mann model with data from individual patients, across different age groups from neonates to adults. Calculating TGCs for each patient of a specific age group provides us with insight into the variability of haemostatic activity across that age group. From our model we observe that two commonly used metrics for haemostatic activity are significantly lower in neonates than in older patients. Because both metrics are strongly determined by prothrombin and prothrombin levels are considerably lower in neonates we conclude that decreased haemostatic activity in neonates is due to lower prothrombin availability.

Prothrombin conversion is accelerated in the antiphospholipid syndrome and insensitive to thrombomodulin

Antiphospholipid syndrome (APS) is a condition in which the presence of antibodies against phospholipid-binding proteins is associated with thrombophilia and/or pregnancy morbidity. Although antiphospholipid antibodies have anticoagulant characteristics in vitro, they are associated with thromboembolic complications. Thrombin generation (TG) is a sensitive global test of coagulation, and elevated TG is associated with thrombosis. Increased TG can be caused by increased prothrombin conversion, decreased thrombin inactivation, or a combination of both. In this study, we measured TG in APS patients and healthy controls with and without vitamin K antagonist (VKA) treatment at 1 and 5 pM tissue factor and with thrombomodulin. Prothrombin conversion and thrombin inactivation were determined by thrombin dynamics analysis. The TG peak was increased in nontreated APS patients at 1 pM TF compared with nontreated controls. Prothrombin conversion was significantly increased in nontreated APS patients. In contrast, prothrombin conversion did not differ in controls and patients that were on VKA therapy. Thrombin inactivation was comparable between controls and APS patients in the presence and absence of VKAs. Both TG (peak and ETP) and prothrombin conversion were significantly higher in APS patients with prior thrombosis compared with patients without a history of thrombosis. In this study, we demonstrate that in APS, the hemostatic balance shifts toward a more prothrombotic phenotype due to elevated prothrombin conversion but unchanged thrombin inactivation rates. Within the group of APS patients, increased TG and prothrombin conversion are associated with a history of thrombosis.

A reduction of prothrombin conversion by cardiac surgery with cardiopulmonary bypass shifts the haemostatic balance towards bleeding

Cardiac surgery with cardiopulmonary bypass (CPB) is associated with blood loss and post-surgery thrombotic complications. The process of thrombin generation is disturbed during surgery with CPB because of haemodilution, coagulation factor consumption and heparin administration. We aimed to investigate the changes in thrombin generation during cardiac surgery and its underlying pro- and anticoagulant processes, and to explore the clinical consequences of these changes using in silico experimentation. Plasma was obtained from 29 patients undergoing surgery with CPB before heparinisation, after heparinisation, after haemodilution, and after protamine administration. Thrombin generation was measured and prothrombin conversion and thrombin inactivation were quantified. In silico experimentation was used to investigate the reaction of patients to the administration of procoagulant factors and/or anticoagulant factors. Surgery with CPB causes significant coagulation factor consumption and a reduction of thrombin generation. The total amount of prothrombin converted and the rate of prothrombin conversion decreased during surgery. As the surgery progressed, the relative contribution of α2-macroglobulin-dependent thrombin inhibition increased, at the expense of antithrombin-dependent inhibition. In silico restoration of post-surgical prothrombin conversion to pre-surgical levels increased thrombin generation excessively, whereas co-administration of antithrombin resulted in the normalisation of post-surgical thrombin generation. Thrombin generation is reduced during surgery with cardiopulmonary bypass because of a balance shift between prothrombin conversion and thrombin inactivation. According to in silico predictions of thrombin generation, this new balance increases the risk of thrombotic complications with prothrombin complex concentrate administration, but not if antithrombin is co-administered.

Decreased prothrombin conversion and reduced thrombin inactivation explain rebalanced thrombin generation in liver cirrhosis

Impaired coagulation factor synthesis in cirrhosis causes a reduction of most pro- and anticoagulant factors. Cirrhosis patients show no clear bleeding or thrombotic phenotype, although they are at risk for both types of hemostatic event. Thrombin generation (TG) is a global coagulation test and its outcome depends on underlying pro- and anticoagulant processes (prothrombin conversion and thrombin inactivation). We quantified the prothrombin conversion and thrombin inactivation during TG in 30 healthy subjects and 52 Child-Pugh (CP-) A, 15 CP-B and 6 CP-C cirrhosis patients to test the hypothesis that coagulation is rebalanced in liver cirrhosis patients. Both prothrombin conversion and thrombin inactivation are reduced in cirrhosis patients. The effect on pro- and anticoagulant processes partially cancel each other out and as a result TG is comparable at 5 pM tissue factor between healthy subjects and patients. This supports the hypothesis of rebalanced hemostasis, as TG in cirrhosis patients remains within the normal range, despite large changes in prothrombin conversion and thrombin inactivation. Nevertheless, in silico analysis shows that normalization of either prothrombin conversion or thrombin inactivation to physiological levels, by for example the administration of prothrombin complex concentrates would cause an elevation of TG, whereas the normalization of both simultaneously maintains a balanced TG. Therefore, cirrhosis patients might require adapted hemostatic treatment.

Developmental hemostasis: A lifespan from neonates and pregnancy to the young and elderly adult in a European white population

Absolute values of reference ranges for coagulation assays in humans vary within the entire lifespan and confirm the concept of developmental hemostasis. It is known that physiologic concentrations of coagulation factors (F) gradually increase over age: they are lower in premature infants as compared to full-term babies, healthy children or adults. Here we demonstrate in a cohort of 1011 blood donors and in a group of 193 healthy pregnant women, that the process of developmental hemostasis proceeds in adults. During the course of pregnancy F and activation markers steadily increase until delivery with a parallel decrease noticed for protein S. From adolescents, young adults to the elderly there is a further increase of F, reaching significance starting between 35 and 50years of age compared to younger subjects. Covering the entire lifespan FVIII and von-Willebrand-factor showed the lowest values in carriers of blood group "O". Apart from pregnancy differences related to gender, pill users, smoking habits or the presence of thrombophilic variants were reported. Laboratory test results should be compared to age-related reference intervals when hemostatic defects are suspected to avoid misclassifications as being "healthy", prone to "bleeding" or vice versa to "thrombosis".