Thromboelastography in children with coagulation factor deficiencies

Assessment of the phenotypic severity of hemophilia A: using rotational thromboelastometry (ROTEM) and APTT-clot waveform analysis

BACKGROUND

Hemophilia A (HA) is an X-linked inherited bleeding disorder caused by reduced factor VIII (FVIII) levels. Approximately 10-15% of patients with severe HA (SHA) do not present with the anticipated bleeding pattern. Here, we assessed the phenotypic severity of hemophilia A using rotational thromboelastometry (ROTEM) and activated partial thromboplastin time-clot waveform analysis (APTT-CWA).

METHODS

Patients diagnosed with hemophilia A were enrolled. Clinical phenotype assignment was performed according to the published literature, and patients were classified into four phenotypic subgroups. The whole blood sample was first run on ROTEM in INTEM mode using platelet-poor plasma, APTT was run, and the APTT-CWA graph was simultaneously recorded.

RESULTS

A total of 66 patients were recruited for this study. Statistically significant differences were observed between the four phenotypically categorized groups using ROTEM and APTT-CWA. On comparing patients with mild/moderate-to-severe phenotypes (Group II) with SHA without inhibitors (Group IV), no significant difference was found for all parameters of ROTEM or APTT-CWA. The MCF, MA30, MAXV, and Alpha angle values using ROTEM were found to be the lowest in patients with SHA with inhibitors, which helped differentiate them from those with SHA without inhibitors. However, these two groups could not be differentiated using the APTT-CWA parameters.

CONCLUSION

ROTEM can be used to distinguish patients with SHA with inhibitors from those with SHA without inhibitors using a combination of parameters with high sensitivity and specificity. However, APTT-CWA cannot be used to differentiate these patient groups.

The role of viscoelastic hemostatic assays for postpartum hemorrhage management and bedside intrapartum care

Viscoelastic hemostatic assays are point-of-care devices that assess coagulation and fibrinolysis in whole blood samples. These technologies provide numeric and visual information of clot initiation, clot strength, and clot lysis under low-shear conditions, and have been used in a variety of clinical settings and subpopulations, including trauma, cardiac surgery, and obstetrics. Emerging data indicate that these devices are useful for detecting important coagulation defects during major postpartum hemorrhage (especially low plasma fibrinogen concentration [hypofibrinogenemia]) and informing clinical decision-making for blood product use. Data from observational studies suggest that, compared with traditional formulaic approaches to transfusion management, targeted or goal-directed transfusion approaches using data from viscoelastic hemostatic assays are associated with reduced hemorrhage-related morbidity and lower blood product requirement. Viscoelastic hemostatic assays can also be used to identify and treat coagulation defects in patients with inherited or acquired coagulation disorders, such as factor XI deficiency or immune-mediated thrombocytopenia, and to assess hemostatic profiles of patients prescribed anticoagulant medications to mitigate the risk of epidural hematoma after neuraxial anesthesia and postpartum hemorrhage after delivery.

Evaluating for Suspected Child Abuse: Conditions That Predispose to Bleeding

Child abuse might be suspected when children present with cutaneous bruising, intracranial hemorrhage, or other manifestations of bleeding. In these cases, it is necessary to consider medical conditions that predispose to easy bleeding or bruising. When evaluating for the possibility of bleeding disorders and other conditions that predispose to hemorrhage, it is important for pediatricians to consider the child's presenting history, medical history, and physical examination findings before initiating a laboratory investigation. Many medical conditions can predispose to easy bleeding. Before ordering laboratory tests for a disease, it is useful to understand the biochemical basis and clinical presentation of the disorder, condition prevalence, and test characteristics. This technical report reviews the major medical conditions that predispose to bruising or bleeding and should be considered when evaluating for abusive injury.

Use of thromboelastography before the administration of hemostatic agents to safely taper recombinant activated factor VII in acquired hemophilia A: a report of three cases

Background

Acquired hemophilia A (AHA) is a rare autoimmune disease characterized by bleeding events. Recombinant activated factor VII (rFVIIa) is a first-line bypassing agent, which is effective against clinically significant bleeding. However, there is no standard way of tapering and discontinuing rFVIIa, mainly because there is no established method for monitoring rFVIIa therapy for AHA.

Case presentation

Here, we report three AHA cases, in which we adjusted the rFVIIa dosing interval based on the results of thromboelastography (TEG) performed just before the administration of the next dose of rFVIIa. The dosing interval of rFVIIa was prolonged based on the reaction rate time (R) according to TEG, which is correlated with coagulation factor activity. The R-value reference range reported by the manufacturer of the TEG system was used as a threshold for making decisions. In these three cases, there was no rebleeding, and the patients’ ability to perform activities of daily living did not decline.

Conclusion

Our cases suggest that conducting TEG-based monitoring just before the administration of the next dose of rFVIIa may be useful for guiding increases in the rFVIIa dosing interval without causing rebleeding events. Further investigations are warranted to examine how TEG could be used to determine the most appropriate rFVIIa dosing interval, e.g., through regular TEG-based monitoring, and the optimal TEG-derived threshold for indicating changes to the rFVIIa dosing interval.

Viscoelastic testing in benign hematologic disorders: Clinical perspectives and future implications of point-of-care testing to assess hemostatic competence

Viscoelastic tests (VETs) have been used routinely for liver transplantation, cardiac surgery, and trauma, but only recently have found clinical utility in benign hematologic disorders. Therefore, guidelines for diagnosis and treatment of these disorders based on viscoelastic variables have been adapted from the existing transplant, cardiothoracic surgery, and trauma resuscitation literature. As a result, diagnostic and therapeutic strategies for benign hematologic disorders utilizing VETs are not uniform. Accordingly, even though there has been a recent increase in the utilization of VET for the diagnosis and treatment of such disorders, the literature is still in its early stages. Analysis of point-of-care viscoelastic tracings from benign hematologic disorders has the potential to allow prompt recognition of disease and to guide patient-specific intervention. Here we present a review describing the application of VETs to benign hematologic disorders.

Bleeding phenotype of patients with moderate haemophilia A and B assessed by thromboelastometry and thrombin generation

INTRODUCTION

Predicting the bleeding phenotype is crucial for the management of patients with moderate haemophilia. Global coagulation assays evaluate haemostasis more comprehensively than conventional methods.

AIM

To explore global coagulation assays and the bleeding phenotype of patients with moderate haemophilia A (MHA) and B (MHB).

METHODS

The MoHem study is a cross-sectional, multicentre study covering Nordic patients with MHA and MHB. Thromboelastometry in whole blood and thrombin generation (TG) in platelet-poor plasma (1, 2.5 and 5 pM tissue factor (TF)) were compared with joint health (Haemophilia Joint Health Score (HJHS)) and treatment modality.

RESULTS

We report on 61 patients from Oslo and Helsinki: 24 MHA and 37 MHB. By TG (2.5 pM TF), patients who had been without replacement therapy during the previous 12 months depicted higher endogenous thrombin potential (P = .03). In contrast, those who had low ETP (< median) captured higher HJHS (P = .02). Patients who had undergone orthopaedic surgery generated least thrombin (P = .02). By thromboelastometry, those without the need of factor consumption had short clotting times, and quick times to maximum velocity (< median values) (P = .03). Factor VIII/factor IX activity (FVIII/FIX:C) did not align with the bleeding phenotype, but FIX:C ≤ 3 IU/dL was associated with lower peak thrombin (P = .03).

CONCLUSION

TG differentiated patients with moderate haemophilia according to HJHS, annual factor consumption, and whether orthopaedic surgery had been performed. Thromboelastometry differentiated according to factor consumption only. Global coagulation assays may assist predicting the bleeding phenotype in moderate haemophilia.

Thrombin activatable fibrinolysis inhibitor pathway alterations correlate with bleeding phenotype in patients with severe hemophilia A

BACKGROUND

Patients with severe hemophilia A display varied bleeding phenotypes despite similar factor VIII (FVIII) activity levels.

OBJECTIVE

We investigated different thrombin activatable fibrinolysis inhibitor (TAFI)-related variables in patients with severe hemophilia A and their possible correlation with bleeding tendency.

PATIENTS/METHODS

Sixty-one patients with severe hemophilia A (FVIII:C <1%], treated on demand, were included. Patients were categorized as mild, moderate, and severe bleeders according to number of bleeds per year (≤2, 3-24, ≥25, respectively). Thirty healthy males served as controls. Clot lysis time was assessed by turbidimetric assay, TAFI activation by two-stage functional assay, and response to TAFIa as the prolongation of fibrinolysis time upon addition of purified TAFIa. Circulating levels of activated TAFI (TAFIa/ai) were measured by specific enzyme-linked immunosorbent assay.

RESULTS

As compared to controls, hemophilic patients displayed shorter lysis time, less TAFIa generation, and reduced response to TAFIa, but similar TAFIa/ai levels. Clot lysis time was similar in mild, moderate, and severe bleeders, whereas TAFIa generation and response to TAFIa decreased with the increase in bleeding tendency; moreover, circulating TAFIa/ai levels were highest in severe bleeders. Patients with markedly impaired TAFIa generation or TAFIa response (below median) displayed 3-fold to 4-fold higher bleeding rate and factor consumption than patients whose TAFI-related values approached the control ones.

CONCLUSION

The TAFI pathway impairment correlates with bleeding phenotype in severe hemophilia and may represent a promising tool to stratify the bleeding risk.

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.

The Utility of Thromboelastography to Guide Blood Product Transfusion

OBJECTIVES

To provide an overview of the clot viscoelastic testing technology and to describe its utility in guiding blood product transfusions.

METHODS

A case scenario will be discussed as well as interpretation of thromboelastography (TEG) tracings. In addition, literature examining the utility of viscoelastic testing in guiding patient management and blood product transfusions will be reviewed.

RESULTS

TEG/rotational thromboelastometry (ROTEM) is useful in evaluating clot kinetics in trauma and acutely bleeding patients. TEG/ROTEM parameters are reflective of values measured using standard coagulation assays; however, TEG/ROTEM parameters are more rapidly available and more costly. TEG and ROTEM are used in three main settings: cardiac surgery, liver transplantation, and trauma to assess global hemostasis and administration of blood products.

CONCLUSIONS

TEG/ROTEM can be helpful in guiding resuscitation and blood product transfusion. Several studies have demonstrated a reduction in transfusion of blood components with TEG/ROTEM; however, other studies have suggested that TEG/ROTEM is not clinically effective in guiding transfusion.

A decreased and less sustained desmopressin response in hemophilia A carriers contributes to bleeding

The cause of hemophilia A carrier bleeding is not well established. Desmopressin (DDAVP), used clinically to treat or prevent bleeding, can also be used as a medical stress surrogate. This study's objective was to compare the response to DDAVP in hemophilia A carriers with that in normal control patients. Bleeding was assessed by the International Society on Thrombosis and Hemostasis Bleeding Assessment Tool (ISTH-BAT). DDAVP (0.3 μg/kg) was administered either IV or subcutaneously (SC), and blood was drawn at baseline and 1, 2, and 4 hours postadministration. Blood was assessed for factor VIII (FVIII) level, von Willebrand factor (VWF) antigen (VWF:Ag), VWF activity (VWF:RCo or VWF:GPIbM), thromboelastography (TEG), and thrombin generation assay (TGA) at all points, and for VWF propeptide (VWFpp):Ag ratio and ABO blood type at baseline. Carriers were older than control patients (median age, 34 and 21 years, respectively; P = .003) and had higher ISTH-BAT bleeding scores (median bleeding score, 8 and 0, respectively; P = .001). Carriers had a significantly reduced FVIII response to DDAVP compared with control patients (P ≤ .0001). When only carriers with normal baseline FVIII levels (n = 10) were included, carriers maintained a reduced FVIII response (P ≤ .0001). Furthermore, participants with abnormal bleeding scores had a significantly lower FVIII response to DDAVP compared with those with normal bleeding scores (P = .036). Hemophilia A carriers have a lower and less sustained FVIII response to DDAVP, suggesting an impaired ability to respond to hemostatic stress, which contributes to bleeding.

A novel, point-of-care, whole-blood assay utilizing dielectric spectroscopy is sensitive to coagulation factor replacement therapy in haemophilia A patients

BACKGROUND

Reliable monitoring of coagulation factor replacement therapy in patients with severe haemophilia, especially those with inhibitors, is an unmet clinical need. While useful, global assays, eg thromboelastography (TEG), rotational thromboelastometry (ROTEM) and thrombin generation assay (TGA), are cumbersome to use and not widely available.

OBJECTIVE

To assess the utility of a novel, point-of-care, dielectric microsensor - ClotChip - to monitor coagulation factor replacement therapy in patients with haemophilia A, with and without inhibitors.

METHODS

The ClotChip T_peak parameter was assessed using whole-blood samples from children with severe haemophilia A, with (n = 6) and without (n = 12) inhibitors, collected pre- and postcoagulation factor replacement therapy. ROTEM, TGA and chromogenic FVIII assays were also performed. Healthy children (n = 50) served as controls.

RESULTS

ClotChip T_peak values exhibited a significant decrease for samples collected postcoagulation factor replacement therapy as compared to baseline (pretherapy) samples in patients with and without inhibitors. A difference in T_peak values was also noted at baseline among severe haemophilia A patients with inhibitors as compared to those without inhibitors. ClotChip T_peak parameter exhibited a very strong correlation with clotting time (CT) of ROTEM, endogenous thrombin potential (ETP) and peak thrombin of TGA, and FVIII clotting activity.

CONCLUSIONS

ClotChip is sensitive to coagulation factor replacement therapy in patients with severe haemophilia A, with and without inhibitors. ClotChip T_peak values correlate very well with ROTEM, TGA and FVIII assays, opening up possibilities for its use in personalized coagulation factor replacement therapy in haemophilia.

Thromboelastometry as a diagnostic tool in mild bleeding disorders: A prospective cohort study

BACKGROUND

Major guidelines emphasise the potential of visco-elastic methods to overcome the limitations of conventional laboratory assays in the peri-operative setting. Their sensitivity regarding mild bleeding disorders (MBDs), the most common bleeding disorders in the general population, is however unknown.

OBJECTIVE

The aim of this study was to investigate the sensitivity of thromboelastometry for diagnosis of MBD.

DESIGN

A single-centre prospective cohort study.

SETTING

Haematology outpatient unit of a tertiary general hospital in Central Switzerland.

PATIENTS

All consecutive patients referred over a 32-month period with a suspected bleeding disorder were included and thromboelastometry was conducted using a ROTEM delta (EXTEM, INTEM and FIBTEM). Diagnostic work-up was performed according to current guidelines including the ISTH bleeding assessment tool (ISTH BAT).

MAIN OUTCOME MEASURES

Distribution of clotting time (CT) and maximum clot firmness (MCF) results in relation to the presence of MBD.

RESULTS

Two hundred and seventeen patients were assessed; the median [IQR] age was 39 years [28 to 57]; 151 patients were women (70%). MBD was diagnosed in 97 patients (45%), no MBD was found in 100 patients (46%) and a systemic disorder recognised in 20 patients (9%). Presence of MBD was not associated with a significant difference in thromboelastometry variables (0.2 s in CT EXTEM, 95% CI -2.3 to 2.7; -0.2 mm in MCF EXTEM, 95% CI -1.8 to 1.5; -0.7 s in CT INTEM, 95% CI -12.6 to 11.2; 0.6 mm in MCF INTEM, 95% CI -1.2 to 1.3; 0.8 mm in MCF FIBTEM, 95% CI -1.6 to 1.4) and most results were within the established reference ranges.

CONCLUSION

Our data did not support the use of thromboelastometry as a diagnostic tool in patients with MBD.

Clinical utility of viscoelastic testing (TEG and ROTEM analyzers) in the management of old and new therapies for hemophilia

Hemophilia A and B are rare inherited bleeding disorders resulting from deficiency of coagulation factors VIII and IX respectively. In the past few decades, the field of hemophilia has witnessed pivotal management challenges and therapeutic advances. Routine coagulation and factor assays, while useful in the classification of severity and treatment monitoring in hemophilia patients, have been shown to be of limited use in managing clinical presentations and outcomes. This prompted the investigation of viscoelastic studies in hemophilia care, which have established their utility in various bleeding and thrombotic states. In this review, we will discuss and critically assess the current literature highlighting the use of viscoelastic studies in various aspects of hemophilia including the determination of clinical phenotype, management of patients with inhibitors, perioperative management, and monitoring of novel agents.

Evaluation of EC50 of factor VIII as predictor of prophylaxis efficacy in patients with severe haemophilia A

Trough factor (F) VIII level is a not reliable bleeding risk indicator to predict prophylaxis efficacy in severe haemophilia A (SHA), therefore, accurate biomarkers are much needed. Thrombelastography (TEG) monitors both thrombin and clot formation addressing the global haemostatic status but its usefulness to tailor prophylaxis in haemophilia has been poorly evaluated. In this study, correspondence between individual pharmacodynamic/pharmacokinetic profile of FVIII and joint condition, physical activity and bleeding phenotype of SHA patients under prophylactic treatment was assessed. Nineteen SHA patients < 18 years old on long-term prophylaxis treatment with FVIII were studied in an observational cross-sectional study. Whole blood was withdrawn before FVIII administration and at five time-points after infusion for a TEG-based pharmacodynamic- and pharmacokinetic-study. Type of prophylaxis and joint condition at inclusion and physical activity as well as onset of treated spontaneous bleeding events in the previous two years were retrospectively assessed. Six patients had suffered at least one treated spontaneous bleeding event and were named as "bleeders". The rest were named as "non-bleeders". Only the half maximal effective concentration of FVIII (FVIII-EC50) for TEG parameters R-time, K-time and α-angle correlated with the bleeding phenotype being significantly higher in bleeders suggestive of a poorer response to FVIII. Poorer joint condition, trough FVIII levels or type of prophylaxis were not definitive predicting variables of bleeding phenotype. In conclusion, this study reveals FVIII-EC50 for the first time as a valuable biomarker to anticipate individual efficacy of prophylaxis in SHA.

Abrogating fibrinolysis does not improve bleeding or rFVIIa/rFVIII treatment in a non-mucosal venous injury model in haemophilic rodents

Essentials The efficacy of systemic antifibrinolytics for hemophilic non-mucosal bleeding is undetermined. The effect of systemically inhibiting fibrinolysis in hemophilic mice and rats was explored. Neither bleeding nor the response to factor treatment was improved after inhibiting fibrinolysis. The non-mucosal bleeding phenotype in hemophilia A appears largely unaffected by fibrinolysis.

SUMMARY

Background Fibrinolysis may exacerbate bleeding in patients with hemophilia A (HA). Accordingly, antifibrinolytics have been used to help maintain hemostatic control. Although antifibrinolytic drugs have been proven to be effective in the treatment of mucosal bleeds in the oral cavity, their efficacy in non-mucosal tissues remain an open question of significant clinical interest. Objective To determine whether inhibiting fibrinolysis improves the outcome in non-mucosal hemophilic tail vein transection (TVT) bleeding models, and to determine whether a standard ex vivo clotting/fibrinolysis assay can be used as a predictive surrogate for in vivo efficacy. Methods A highly sensitive TVT model was employed in hemophilic rodents with a suppressed fibrinolytic system to examine the effect of inhibiting fibrinolysis on bleeding in non-mucosal tissue. In mice, induced and congenital hemophilia models were combined with fibrinolytic attenuation achieved either genetically or pharmacologically (tranexamic acid [TXA]). In hemophilic rats, tail bleeding was followed by whole blood rotational thromboelastometry evaluation of the same animals to gauge the predictive value of such assays. Results The beneficial effect of systemic TXA therapy observed ex vivo could not be confirmed in vivo in hemophilic rats. Furthermore, neither intravenously administered TXA nor congenital knockout of the fibrinolytic genes encoding plasminogen or tissue-type plasminogen activator markedly improved the TVT bleeding phenotype or response to factor therapy in hemophilic mice. Conclusions The findings here suggest that inhibition of fibrinolysis is not effective in limiting the TVT bleeding phenotype of HA rodents in non-mucosal tissues.

Evaluation of recombinant factor VIII Fc (Eloctate) activity by thromboelastometry in a multicenter phase 3 clinical trial and correlation with bleeding phenotype

The aim of this study was to compare the hemostatic efficacy of recombinant factor VIII Fc (rFVIIIFc) (Eloctate) and Advate by ex-vivo rotation thromboelastometry (ROTEM) of whole blood and to explore potential ROTEM parameters that may be more predictive of a patient's bleeding tendency than plasma FVIII activity. Thirteen clinical sites were selected to perform ROTEM on freshly collected blood samples from 44 patients in the phase 3 study for rFVIIIFc, including 16 patients undergoing sequential pharmacokinetic assessment of Advate and rFVIIIFc. Equivalent hemostatic activity was observed for rFVIIIFc and Advate in postinfusion samples, followed by improvements for rFVIIIFc in clotting time, clot formation time and alpha angle (α) for a longer duration than Advate, consistent with the pharmacokinetic improvements reported previously for rFVIIIFc. Our study did not demonstrate a statistical correlation between a patient's ROTEM activity at baseline or at trough and the occurrence of spontaneous bleeds while on prophylactic therapy. However, an association was observed between postinfusion clotting time and the occurrence of one or more spontaneous bleeds vs. no bleeds over a follow-up period of 1 year (P = 0.003). How well a patient's whole blood clotting deficiency is corrected after a dose of FVIII may be an indicator of subsequent bleeding tendency in patients with otherwise equivalent FVIII peak and trough levels. The technical challenges of standardizing the ROTEM, largely overcome in the current study, may however preclude the use of this method for widespread assessment of global hemostasis unless additional assay controls or normalization procedures prove to be effective.

Clot stability as a determinant of effective factor VIII replacement in hemophilia A

Background

Factor VIII (FVIII) replacement is standard of care for patients with hemophilia A (HemA); however, patient response does not always correlate with FVIII levels. We hypothesize this may be in part due to the physical properties of clots and contributions of fibrin, platelets, and erythrocytes, which may be important for hemostasis.

Objective

To understand how FVIII contributes to effective hemostasis in terms of clot structure and mechanical properties.

Patients/Methods

In vitro HemA clots in human plasma or whole blood were analyzed using turbidity waveform analysis, confocal microscopy, and rheometry with or without added FVIII. In vivo clots from saphenous vein puncture in wild-type and HemA mice with varying FVIII levels were examined using scanning electron microscopy.

Results

FVIII profoundly affected HemA clot structure and physical properties; added FVIII converted the open and porous fibrin meshwork and low stiffness of HemA clots to a highly branched and dense meshwork with higher stiffness. Platelets and erythrocytes incorporated into clots modulated clot properties. The clots formed in the mouse saphenous vein model contained variable amounts of compressed erythrocytes (polyhedrocytes), fibrin, and platelets depending on the levels of FVIII, correlating with bleeding times. FVIII effects on clot characteristics were dose-dependent and reached a maximum at ~25% FVIII, such that HemA clots formed with this level of FVIII resembled clots from unaffected controls.

Conclusions

Effective clot formation can be achieved in HemA by replacement therapy, which alters the architecture of the fibrin network and associated cells, thus increasing clot stiffness and decreasing clot permeability.

The utility of thromboelastography in inherited and acquired bleeding disorders

Thromboelastography (TEG) was first described by Hartert in 1948, and was designed to monitor viscoelastic clot strength in whole blood in real time. The current TEG method and Rotational Thromboelastometry (ROTEM) were subsequently developed from the original principles. Both of the modern methods provide data by measuring changes in the viscoelastic strength of a small sample of clotting blood in response to a constant rotational force. The important advantage of these techniques is to visually observe and quantify blood coagulation including the propagation, stabilization and dissolution phases of clot formation under low shear conditions. Analysis of the results provides detailed kinetic data on fibrin generation, clot strength and fibrinolysis. These TEG/ROTEM analyses therefore enable evaluation of global clotting function and the monitoring of haemostatic treatment in various clinical situations, not only in patients with genetic bleeding disorders, such as haemophilia, but also in patients undergoing cardiac surgery, liver transplantation or suffering from traumatic injury. Some evidence suggests that haemostatic management using TEG/ROTEM leads to a reduction in total transfusions of whole blood or clotting factors. Wider clinical application of this technology seems likely.

Challenges of diagnosing and managing the adolescent with heavy menstrual bleeding

Unpredictable, prolonged or heavy menstrual bleeding (HMB) may be expected for many adolescents soon after menarche. A decade of clinical experience and research has now established firmly that bleeding disorders (BD) are common in adolescents with HMB. Despite these advances, many questions remain, and several aspects of the diagnosis and management of BDs in adolescents are not supported by rigorous clinical trials. In this overview, four major areas will be discussed. First, we will discuss the frequency of BDs in young women with HMB. Up to 20% of older females with HMB are thought to have an underlying BD. Estimates from retrospective studies in adolescents suggest a prevalence that varies anywhere from 10 to 62%. Prospective studies with uniform hemostatic evaluation are needed to answer this question definitively. Second, we will review existing tools that help screen and diagnose adolescents with HMB with an underlying BD. Although identification of an underlying BD in older women with HMB is relatively straight forward, uncertainties remain for adolescents. Heavy menstrual bleeding in this age group may have different pathophysiological underpinnings than those in older women and may often be disregarded as anovulatory. There is an urgent need to develop novel tools, and evaluate existing diagnostic strategies in adolescents. Third, we will discuss the optimal medical management of HMB in young adolescents. As direct evidence is largely lacking, these areas are also subject to extrapolation from older women. Lastly, an important area- prediction, and management of future bleeding in those adolescents who are diagnosed with a mild BD-will be discussed. Throughout, areas of controversy and opportunities for further research are highlighted.

Verifying the performance characteristics of the TEG5000 thromboelastogram in the clinical laboratory

OBJECTIVE

To verify the manufacturer performance claims of the TEG5000 with traditional laboratory methods.

MATERIALS AND METHODS

Samples were concurrently measured using the TEG5000 analyzer and either PT, APTT, fibrinogen, factor activities, platelet count, or platelet function testing using whole blood or platelet-rich plasma methods.

RESULTS

Within-run imprecision yielded coefficient of variation (CV) of <5%. There was no correlation of PT or APTT with R time. Only Factor VIII and factor XII activity significantly correlated with R time. There was significant correlation between k and angle with FBG, PLT count, and factor levels. There was weak inverse correlation between angle results and measures of platelet function. All laboratory methods were significantly correlated with MA. There were significant differences between citrated whole blood and fresh citrated plasma for angle and MA, and between fresh and frozen plasma for R time and MA. We demonstrated a high % inhibition noted with normal, drug naïve donors, especially with ADP PLT mapping (50% inhibition), but less so with AA PLT mapping (20% inhibition). For TEG platelet mapping, 19/22 (86.3%) and 17/22 (77.3%) results were concordant with traditional aggregation results.

CONCLUSION

We demonstrated both the lack of, and strong correlation between laboratory tests and the TEG parameters.

Global assays in hemophilia

The quest for the ideal method to study hemostasis in the evaluation and management of patients with bleeding disorders such as hemophilia is an ongoing effort. With the rapid evolution of biotechnology and the emergence of several new products for treatment of patients with hemophilia with and without inhibitors, there is a great need for tests that can be used to reliably evaluate and monitor our interventions. Global assays in coagulation allow the study of the interaction between the components involved in the process of hemostasis and are therefore considered by many to be more reflective of the in vivo hemostatic mechanism. Here we provide a brief review of the most widely used global assays in hemostasis (thrombin generation and thromboelastography) and their utility in the evaluation and management of hemophilia.

Integration of acoustic radiation force and optical imaging for blood plasma clot stiffness measurement

Despite the life-preserving function blood clotting serves in the body, inadequate or excessive blood clot stiffness has been associated with life-threatening diseases such as stroke, hemorrhage, and heart attack. The relationship between blood clot stiffness and vascular diseases underscores the importance of quantifying the magnitude and kinetics of blood's transformation from a fluid to a viscoelastic solid. To measure blood plasma clot stiffness, we have developed a method that uses ultrasound acoustic radiation force (ARF) to induce micron-scaled displacements (1-500 μm) on microbeads suspended in blood plasma. The displacements were detected by optical microscopy and took place within a micro-liter sized clot region formed within a larger volume (2 mL sample) to minimize container surface effects. Modulation of the ultrasound generated acoustic radiation force allowed stiffness measurements to be made in blood plasma from before its gel point to the stage where it was a fully developed viscoelastic solid. A 0.5 wt % agarose hydrogel was 9.8-fold stiffer than the plasma (platelet-rich) clot at 1 h post-kaolin stimulus. The acoustic radiation force microbead method was sensitive to the presence of platelets and strength of coagulation stimulus. Platelet depletion reduced clot stiffness 6.9 fold relative to platelet rich plasma. The sensitivity of acoustic radiation force based stiffness assessment may allow for studying platelet regulation of both incipient and mature clot mechanical properties.

Specific and global coagulation tests in patients with mild haemophilia A with a double mutation (Glu113Asp, Arg593Cys)

BACKGROUND

Heterogeneous bleeding phenotypes are observed in haemophilia A patients with the same mutation in the F8 gene. Specific mutations in the A2 domain of factor VIII are associated with mild haemophilia and a higher risk of inhibitor development. Double mutations in mild haemophilia A are rarely reported. In this study, we investigated the in vitro function of factor VIII, performing different specific and global coagulation assays, observed clinical characteristics and assessed the possible predictive diagnostic value of the differences.

MATERIALS AND METHODS

The clinical features of haemophiliacs with a mild phenotype were reviewed. Blood samples were obtained and analysed for mutations and coagulation assays: activated partial thromboplastin time, one-stage and chromogenic factor VIII activity, factor VIII antigen and rotational thromboelastometry.

RESULTS

We report on a cohort of 22 patients with double Glu113Asp, Arg593Cys mutations. All our patients have a quantitative defect of factor VIII and preserved similar functional activity. Factor VIII activities measured by the one-stage or chromogenic method were not discrepant, although the chromogenic assay resulted in 20% lower factor VIII activities. Waveform analysis showed a lower maximum value of the second derivative curve (Max2) of APTT with curve shape alternation, while thromboelastometry (INTEM) showed low sensitivity in comparison to results in a normal population.

DISCUSSION

In genotyping, the coexistence of a second mutation should never be excluded, especially in cases of discordant clinical presentation. Waveform analysis correlates better with factor VIII activity than thromboelastometry and the Max2 parameter could provide additional information in managing haemophilia patients. The utility of specific factor activity and global haemostatic assays in general practice still needs to be investigated.

Trauma induced hypercoagulablity in pediatric patients

PURPOSE

Coagulation changes in pediatric trauma patients are not well defined. To fill this gap, we tested the hypothesis that trauma evokes a hypercoagulable response.

METHODS

A prospective observational study was conducted in hospitalized patients (age 8months to 14years) admitted for trauma or elective surgery. Informed consent was obtained from the parents and informed assent was obtained in patients 7years of age or older. Coagulation changes were evaluated on fresh whole blood using thromboelastography (TEG) and on stored plasma using assays for special clotting factors.

RESULTS

Forty three patients (22 trauma, median injury severity score =9; and 21 uninjured controls) were evaluated. For trauma vs control, prothrombin time (PT) was higher by about 10% (p<0.001), but activated partial thromboplastin time was not altered. TEG clotting time (R;p=0.005) and fibrin cross-linking were markedly accelerated (K time, alpha angle; p<0.001) relative to the control patients. d-Dimer, Prothrombin Fragment 1+2, and Plasminogen Activator Inhibitor-1 were all elevated, whereas Protein S activity was reduced (all p<0.01). Importantly, a large fraction of TEG values and clotting factor assays in the pediatric control group were outside the published reference ranges for adults.

CONCLUSION

A hypercoagulable state is associated with minor trauma in children. More work is needed to determine the functional significance of these changes and to establish normal pediatric reference ranges.

A novel approach for detecting hypercoagulability utilizing thromboelastography

INTRODUCTION

The thromboelastograph is a point-of-care, global hemostasis assay that measures the dynamics of clot formation, including physical properties, over time and is licensed for use in monitoring coagulation during complex surgical procedures. It has more recently been used as a research tool to investigate various bleeding and clotting disorders. Although attempts have been made to use thromboelastography to detect hypercoagulable states, thus far a consistent, reliable approach has not been discovered. The objective of this study was to develop a novel approach utilizing thromboelastography that is sensitive for detecting hypercoagulability.

MATERIALS AND METHODS

Healthy, adult volunteers provided blood samples that were subjected to pre-analytic modifications from standard thromboelastography methods with the goal of prolonging clot initiation and propagation times. The methods which resulted in the desired changes in a consistent and reliable manner utilized corn trypsin inhibitor, a contact pathway inhibitor, on unactivated blood samples. To demonstrate that these methods are sensitive to detecting hypercoagulability, increasing concentrations of recombinant human thrombin were added as a surrogate for hypercoagulability.

RESULTS

Our methods were able to consistently and statistically significantly change the baseline TEG parameters of R time, K time, and angle in the desired fashion. Additionally, these methods were able to detect increasing concentrations of thrombin.

CONCLUSIONS

We describe a novel approach in which thromboelastography is highly sensitive to detecting increasing concentrations of thrombin in vitro. Further studies are underway to determine if these methods will be sensitive for detecting hypercoagulable states in vivo.

Thrombin generation and whole blood viscoelastic assays in the management of hemophilia: current state of art and future perspectives

Hemophilia is a bleeding disorder that afflicts about 1 in 5000 males. Treatment relies upon replacement of the deficient factor, and response to treatment both in clinical research and practice is based upon subjective parameters such as pain and joint mobility. Existing laboratory assays quantify the amount of factor in plasma, which is useful diagnostically and prognostically. However, these assays are limited in their ability to fully evaluate the patient's clot-forming capability. Newer assays, known as global assays, provide a far more detailed view of thrombin generation and clot formation and have been studied in hemophilia for about 10 years. They have the potential to offer a more objective measure of both the hemophilic phenotype as well as the response to treatment. In particular, in patients who develop inhibitors to deficient clotting factors and in whom bypassing agents are required for hemostasis, these assays offer the opportunity to determine the laboratory response to these interventions where traditional coagulation assays cannot. In this article we review the existing literature and discuss several controversial issues surrounding the assays. Last, a vision of future clinical uses of these assays is briefly described.

Global haemostasis and point of care testing

The evaluation of the coagulation profile has used so far either clotting-based or chromogenic assays with different endpoints. Clotting-based techniques are the most used worldwide, and they certainly are useful for diagnosis of clotting factor deficiencies. However, the information provided is relatively limited, and therefore the individual profile of coagulation is poorly assessed. This is reflected by the weak correlation between the results of these assays and the clinical phenotype. Among the assays that benefited from technological advances, thrombin generation and thromboelastography are probably the most actively investigated, but they require specific instruments and are not fully automated. Their standardisation level is rapidly progressing, and they are progressively entering the clinical scene, with the attempt to provide additional information on the coagulation process and a meaningful clinical correlation. These inherited bleeding disorders frequently require replacement therapy using clotting factor concentrates that increase the plasma level of the missing clotting factor. The classical adjustment of the therapy is mainly based on the measurement of the plasma clotting activity of the protein administered. If one considers that a certain level of thrombin generated would predict clinical efficacy, monitoring of thrombin formation might offer new possibilities to individually predict the bleeding phenotype, select the most adapted therapeutic product and tailor the dose. The same holds true for thromboelastography/thromboelastometry which evaluate fibrin formation as well as clot resistance to fibrinolytic challenge, one step further down in the coagulation process. In this regard, these 2 assays could be seen as complementary in terms of information provided on the coagulation profile at the individual level.

A standardized technique for performing thromboelastography in rodents

Thromboelastography (TEG), used in liver transplant and cardiac surgery for nearly 50 years, has recently been applied to the trauma setting. Rodents are used widely for shock research, but are known to have differences in their coagulation system compared with humans. Consequently, the appropriate technique for performing TEG requires modification of the standard clinical protocol. Thromboelastography was performed with blood collected from the femoral artery of rodents, and technical modifications were tested to optimize results. Analysis of citrated whole blood using TEG revealed a more rapid onset of coagulation in rats compared with humans. The reference ranges of TEG parameters for Sprague-Dawley rats are detailed. Citrated native whole blood is the optimal TEG method in the assessment of coagulation in rodents. Investigators using TEG for research purposes should establish their own reference ranges to determine normal values for their target population.

Aptamer ARC19499 mediates a procoagulant hemostatic effect by inhibiting tissue factor pathway inhibitor

Hemophilia A and B are caused by deficiencies in coagulation factor VIII (FVIII) and factor IX, respectively, resulting in deficient blood coagulation via the intrinsic pathway. The extrinsic coagulation pathway, mediated by factor VIIa and tissue factor (TF), remains intact but is negatively regulated by tissue factor pathway inhibitor (TFPI), which inhibits both factor VIIa and its product, factor Xa. This inhibition limits clot initiation via the extrinsic pathway, whereas factor deficiency in hemophilia limits clot propagation via the intrinsic pathway. ARC19499 is an aptamer that inhibits TFPI, thereby enabling clot initiation and propagation via the extrinsic pathway. The core aptamer binds tightly and specifically to TFPI. ARC19499 blocks TFPI inhibition of both factor Xa and the TF/factor VIIa complex. ARC19499 corrects thrombin generation in hemophilia A and B plasma and restores clotting in FVIII-neutralized whole blood. In the present study, using a monkey model of hemophilia, FVIII neutralization resulted in prolonged clotting times as measured by thromboelastography and prolonged saphenous-vein bleeding times, which are consistent with FVIII deficiency. ARC19499 restored thromboelastography clotting times to baseline levels and corrected bleeding times. These results demonstrate that ARC19499 inhibition of TFPI may be an effective alternative to current treatments of bleeding associated with hemophilia.

Standardization of thromboelastography: a report from the TEG-ROTEM working group

Laboratory evaluation of bleeding disorders has been performed with the standard clotting assays such as the PT and PTT for several decades. Our improved understanding of the process of blood coagulation has now revealed the important role played by the cellular elements such as platelets, monocytes and red blood cells. The need for a test that can assess clotting in a more 'global' manner, beyond the initiation of clot formation, has led to greater interest in assays such as thrombin generation and thromboelastography. Even though there are several publications using thromboelastography it remains a research tool as the methodology is not standardized. In an attempt to show reproducibility and consistency using thromboelastography, a group of investigators from different countries joined hands to form the TEG-ROTEM Working Group. Two studies were performed using PRP and FVIII deficient plasma and an intrinsic pathway activator. This article summarizes the results of the first international effort at standardization of thromboelastography. Both of the instruments using this technology (TEG(®) and ROTEM(®)) were used. Nine laboratories from countries around the globe participated in this effort. The results showed a significant inter-laboratory variance with CV's greater than 10%. Although these results were not satisfactory, this has been the first effort to standardize this methodology and significant work remains to be done to improve reliability and reproducibility. These studies were performed on PRP and the results may be more reliable when preformed on whole blood samples. We believe that it is important to continue this work so that we may investigate the usefulness and potential applications of thromboelastography in the evaluation of bleeding and thrombosis.

Global hemostasis testing thromboelastography: old technology, new applications

Thromboelastography (TEG) as a method of assessing global hemostatic and fibrinolytic function has existed for more than 60 years. Improvements in TEG technology have led to increased reliability and thus increased usage. The TEG has been used primarily in the settings of liver transplant and cardiac surgery, with proven utility for monitoring hemostatic and fibrinolytic derangements. In recent years, indications for TEG testing have expanded to include managing extracorporeal membrane oxygenation (ECMO) therapy, assessing bleeding of unclear etiology, and assessing hypercoagulable states. In addition, TEG platelet mapping has been utilized to monitor antiplatelet therapy. Correlation between TEG platelet mapping and other platelet function tests such as the PFA-100 or platelet aggregation studies, however, has not been evaluated fully for clinical outcomes, and results may not be comparable. In general, the advantages of the TEG include evaluation of global hemostatic function using whole blood, a quick turn-around-time, the possibility of both point-of-care-testing and performance in central laboratories, the ability to detect hyperfibrinolysis, monitoring therapy with recombinant activated factor VII, and detection of low factor XIII activity. Potential applications include polycythemia and dysfibrinogenemia. Disadvantages of TEG include a relatively high coefficient of variation, poorly standardized methodologies, and limitations on specimen stability of native whole blood samples. In the pediatric setting, an additional advantage of the TEG is a relatively small sample volume, but a disadvantage is the difference in normal ranges between infants, especially newborns, and adults. In summary, TEG is an old concept with new applications that may provide a unique perspective on global hemostasis in various clinical settings.