Challenges in the laboratory analyses of bleeding disorders

BIVV001, a new class of factor VIII replacement for hemophilia A that is independent of von Willebrand factor in primates and mice

Factor VIII (FVIII) replacement products enable comprehensive care in hemophilia A. Treatment goals in severe hemophilia A are expanding beyond low annualized bleed rates to include long-term outcomes associated with high sustained FVIII levels. Endogenous von Willebrand factor (VWF) stabilizes and protects FVIII from degradation and clearance, but it also subjects FVIII to a half-life ceiling of ∼15 to 19 hours. Increasing recombinant FVIII (rFVIII) half-life further is ultimately dependent upon uncoupling rFVIII from endogenous VWF. We have developed a new class of FVIII replacement, rFVIIIFc-VWF-XTEN (BIVV001), that is physically decoupled from endogenous VWF and has enhanced pharmacokinetic properties compared with all previous FVIII products. BIVV001 was bioengineered as a unique fusion protein consisting of a VWF-D'D3 domain fused to rFVIII via immunoglobulin-G1 Fc domains and 2 XTEN polypeptides (Amunix Pharmaceuticals, Inc, Mountain View, CA). Plasma FVIII half-life after BIVV001 administration in mice and monkeys was 25 to 31 hours and 33 to 34 hours, respectively, representing a three- to fourfold increase in FVIII half-life. Our results showed that multifaceted protein engineering, far beyond a few amino acid substitutions, could significantly improve rFVIII pharmacokinetic properties while maintaining hemostatic function. BIVV001 is the first rFVIII with the potential to significantly change the treatment paradigm for severe hemophilia A by providing optimal protection against all bleed types, with less frequent doses. The protein engineering methods described herein can also be applied to other complex proteins.

Thrombin generation test: A reliable tool to evaluate the pharmacodynamics of vitamin K antagonist rodenticides in rats

Vitamin K antagonist rodenticide pharmacodynamics (PD) is studied in rodents with traditional laboratory tests. We wondered if thrombin generation test (TGT) could add value. Difethialone (10 mg/kg) was administered per os to 97 OFA-Sprague Dawley rats. PD was studied over a 72 h-period using the Calibrated Automated Thrombogram on platelet poor plasma before and after intoxication (3 female and 3 male rats for each 13 time points) and TGT parameters were compared with the prothrombin time (PT) and vitamin K dependent factor activities previously reported. Following intoxication, preliminary tests evidenced rapid and full inhibition of thrombin generation triggered with 5 or 20 pM human recombinant tissue factor. To study the evolution of TGT parameters following difethialone intake, we adapted the test by complementing intoxicated rat samples with pooled normal rat plasma (3/1, v/v). Adapted TGT confirmed the known higher procoagulant basal level in females compared to males through higher endogenous thrombin potential (ETP) and peak height (PH) (p < 0.0001 and p = 0.0003, respectively). An exponential model fitted well the PH and ETP decay after intoxication. In contrast to PT, the decreases were observed immediately following VKA intake and had comparable time to halving values: 10.5 h (95% CI [8.2; 13.6]) for ETP and 10.4 h (95% CI [7.8; 14.1]) for PH. The decrease of FVII and FX preceded that of PH, ETP and FII while FIX decreased later on, contributing to the severe hypo-coagulability. We demonstrated that TGT performed in samples of intoxicated rats complemented with normal plasma is a reliable tool for evaluation of VKA rodenticide PD in rats.

Global hemostatic assay of different target procoagulant activities of factor VIII and factor IX

Background

Korean National Health Insurance reimburses factor VIII (FVIII) and factor IX (FIX) clotting factor concentrate (CFC) infusions to discrepant activity levels, allowing elevation of FVIII activity to 60 IU/dL and FIX to 40 IU/dL. We aimed to assess hemostatic response to these target levels using global hemostatic assays.

Methods

We enrolled 34 normal healthy men, 34 patients with hemophilia A, and 36 with hemophilia B, with residual factor activity of 3 IU/dL or less and without inhibitors. Patients with hemophilia A and B received injected CFCs according to reimbursement guidelines. Fifteen minutes after injection, we assessed hemostatic response with global hemostatic assays: thrombin generation assay (TGA), thromboelastography (TEG), and clot waveform analysis (CWA).

Results

Normal healthy men and patients with hemophilia A and B were 36.7, 37.2, and 35.1 years old, respectively. FVIII and recombinant FIX concentrate doses were 28.8 IU/kg and 43.6 IU/kg. Post-infusion FVIII activity rose from 0.5 IU/dL to 69.4 IU/dL, while FIX activity rose from 1.4 IU/dL to 46.8 IU/dL. Post-infusion peak thrombin concentrations in hemophilia A and B were 116.6 nM/L and 76.4 nM/L (P<0.001). Post-infusion endogenous thrombin potential (ETP) in hemophilia A and B was 1349.8 nM/min and 915.6 nM (P<0.001). TEG index of hemophilia A and B was 0.11 and −0.51 (P=0.006).

Conclusion

Current reimbursed doses for FIX concentrates are insufficient to achieve hemostatic responses comparable to those after reimbursed doses for FVIII concentrates in terms of peak thrombin concentration, ETP, and TEG index.

Treatment and Prevention of Bleeds in Haemophilia Patients with Inhibitors to Factor VIII/IX

The development of alloantibodies neutralising therapeutically administered factor (F) VIII/IX (inhibitors) is currently the most severe complication of the treatment of haemophilia. When persistent and at a high titre, inhibitors preclude the standard replacement treatment with FVIII/FIX concentrates, making patients’ management challenging. Indeed, the efficacy of bypassing agents, i.e., activated prothrombin complex concentrates (aPCC) and recombinant activated factor VII (rFVIIa), needed to overcome the haemostatic interference of the inhibitor, is not comparable to that of factor concentrates. In addition, the therapeutical response is unpredictable, with a relevant inter-individual and even intra-individual variability, and no laboratory assay is validated to monitor the efficacy and safety of the treatment. As a result, inhibitor patients have a worse joint status and quality of life compared to inhibitor-free subjects and the eradication of the inhibitor by immune tolerance induction is the preeminent therapeutic goal, particularly in children. However, over the last decades, treatment with bypassing agents has been optimised, allowing home treatment and the individualisation of regimens aimed at improving clinical outcomes. In this respect, a growing body of evidence supports the efficacy of prophylaxis with both bypassing agents in reducing bleeding rates and improving the quality of life, although the impact on long-term outcomes (in particular on preventing/reducing joint deterioration) is still unknown. This review offers an update on the current knowledge and practice of the use of bypassing agents in haemophiliacs with inhibitors, as well as on debated issues and unmet needs in this challenging setting.

Laboratory evaluation of patients with undiagnosed bleeding disorders

The evaluation of patients with a bleeding tendency represents a challenge as the routinely available tests for evaluating bleeding disorders are limited, complicating the laboratory determination of the clinically observed bleeding tendency. As a result, some bleeding disorders remain undiagnosed. The aim of the study was to evaluate whether global coagulation tests would contribute to the laboratory analysis of patients with undiagnosed bleeding disorders. Patients were evaluated for coagulation and fibrinolysis activities by thrombin generation test and euglobulin lysis time. In addition, plasma activity of factor XIII, plasminogen, α-2 antiplasmin, plasminogen activator inhibitor-1, and thrombin-activatable fibrinolysis inhibitor was also obtained. Forty-five patients were included. Eight per cent presented a mild bleeding disorder and 20% a moderate bleeding disorder. The thrombin generation test results were similar between patients and controls. Euglobulin lysis time results, however, were lower in patients than in controls, both before (median 175 vs. 250 min, respectively; P = 0.003) and after (median 145 vs. 115 min, respectively; P ≤ 0.001) arm constriction, suggesting that they were experiencing hyperfibrinolysis. Interestingly, patients' median thrombin-activatable fibrinolysis inhibitor activity was higher than in controls (21.2 vs. 19.46 μg/ml; P = 0.016). However, plasminogen, α-2 antiplasmin, plasminogen activator inhibitor-1, and factor XIII activities did not differ between the groups. Global coagulation and fibrinolysis tests proved to be limited in detecting the hemostatic disorders in some patients with a relevant bleeding tendency and may not be adequate to address their bleeding risk. Bleeding scores are currently the available medical approach for the evaluation of these patients.

Effects of age and sex on the single-dose pharmacokinetics and pharmacodynamics of apixaban

BACKGROUND AND OBJECTIVES

The effects of age and sex on apixaban pharmacokinetics and pharmacodynamics were studied.

METHODS

This was an open-label, single-dose, 2 × 2 factorial study. Healthy young (aged 18-40 years) and elderly (aged ≥ 65 years) male and female subjects received a single oral 20 mg dose of apixaban. Blood and urine samples were collected for pharmacokinetic and pharmacodynamic (blood only) analyses. Subjects were monitored for adverse events throughout the study.

RESULTS

Seventy-nine subjects were enrolled into four groups: young males (n = 20), elderly males (n = 20), young females (n = 20) and elderly females (n = 19). Age did not affect the maximum observed plasma concentration (C max). The mean area under the concentration-time curve from time zero extrapolated to infinite time (AUC∞) was 32% greater in elderly subjects than in young subjects. The mean C max and AUC∞ values were 18 and 15% higher, respectively, in females than in males. The time course of the mean international normalized ratio (INR), modified prothrombin time (mPT) and anti-Xa activity tracked the apixaban concentration-time curve. All three pharmacodynamic measures exhibited a positive linear correlation with the plasma apixaban concentration. Differences in the mean INR, mPT and anti-Xa activity between age and sex groups were small (<15% at the maximum mean values) and were generally related to pharmacokinetic differences. However, anti-Xa activity demonstrated less variability than the INR or mPT, and may have utility as a bioassay for apixaban. Apixaban was well tolerated, with no serious adverse events.

CONCLUSION

There were no clinically meaningful age- or sex-related differences in the pharmacokinetics and pharmacodynamics of apixaban that would require dose modification on the basis of age or sex alone.

Validation of a modified thromboelastometry approach to detect changes in fibrinolytic activity

Background

Thus far, validated whole blood assays used in in vitro fibrinolysis experiments using thromboelastometry (ROTEM) are lacking or have yet to be tested in humans.

The objective was first, to establish a standardized modified ROTEM approach to detect both hypo- and hyperfibrinolysis. And second, to perform a technical and clinical validation of the assay.

Methods

Blood was used of healthy volunteers, patients with sepsis, patients after cardiothoracic surgery, pregnant women, and cirrhotic liver disease patients. A whole blood tissue factor (TF) activated ROTEM assay with and without the addition of recombinant tissue plasminogen activator (rTPA) was developed. Plasma fibrinolysis determinants were measured in all volunteers and patients.

Results

Thirty five pM TF and additions of 125 and 175 ng/ml rTPA resulted in full lysis within 60 min in healthy volunteers. Coefficients of variation were below 10 % without and below 20 % with rTPA addition. In sepsis the hypofibrinolytic ROTEM profiles with 175 ng/ml rTPA were in line with the plasma determinants (high PAI-1, high fibrinogen, low tPA activity, and high d-dimers). After cardiothoracic surgery, reduced fibrinogen and platelet levels accounted for the reduced maximum clot firmness. The hypofibrinolytic profile is attributed to tranexamic acid use and elevated PAI-1 levels. The lowest rTPA concentration in cirrhosis resulted in hyperfibrinolysis in only few of the patients. In pregnancy normal profiles were found.

Discussion

Our high rTPA concentration demonstrates hypofibrinolytic profiles adequately in sepsis and after cardiothoracic surgery. Our low rTPA concentration of 125 ng/ml seems too high for demonstrating hyperfibrinolysis in cirrhotic liver disease.

Conclusions

We were able to present a validated whole blood ROTEM approach to fibrinolysis testing using added rTPA, which can be of added value next to classical plasma based fibrinolysis assays.

Rotational thromboelastometry in the diagnosis of coagulopathy in major pediatric surgical operations

OBJECTIVES

To examine the correlation between rotational thromboelastometry (ROTEM) and coagulopathy after major pediatric surgical operations.

METHODS

From November 2013 until April 2015, pediatric cases who underwent major noncardiac surgeries and met the coagulopathy-risk criteria were reviewed for postoperative clinically significant coagulopathy (CSC). Two ROTEM studies, EXTEM and INTEM, were performed at the immediately postoperatively without the results being taken into any clinical decision making.

RESULTS

Seventy-seven operations on 73 patients were included in this analysis. CSC occurred following 24 operations (32%) with a significantly higher incidence when a patient had a higher coagulopathy risk. On univariate analysis, evidence of diffuse bleeding in the operative field and massive bleeding were the 2 parameters with the strongest association with CSC. INTEM and EXTEM had specificities in diagnosing CSC of 75.5% and 94.3%, respectively. When each individual EXTEM and INTEM item was analyzed against CSC using ROC analysis, clot forming time (CFT) gave the largest under the curve area. The cut-off CFTs that gave the highest sensitivity and specificity in this study were 120seconds for EXTEM and 100seconds for INTEM.

CONCLUSION

Postoperative coagulopathy is a risk that should always be considered in pediatric surgical operations. Thromboelastometry can be a hemostatic test providing high predictive value for this condition.

The simultaneous occurrence of both hypercoagulability and hypofibrinolysis in blood and serum during systemic inflammation, and the roles of iron and fibrin(ogen)

Although the two phenomena are usually studied separately, we summarise a considerable body of literature to the effect that a great many diseases involve (or are accompanied by) both an increased tendency for blood to clot (hypercoagulability) and the resistance of the clots so formed (hypofibrinolysis) to the typical, 'healthy' or physiological lysis. We concentrate here on the terminal stages of fibrin formation from fibrinogen, as catalysed by thrombin. Hypercoagulability goes hand in hand with inflammation, and is strongly influenced by the fibrinogen concentration (and vice versa); this can be mediated via interleukin-6. Poorly liganded iron is a significant feature of inflammatory diseases, and hypofibrinolysis may change as a result of changes in the structure and morphology of the clot, which may be mimicked in vitro, and may be caused in vivo, by the presence of unliganded iron interacting with fibrin(ogen) during clot formation. Many of these phenomena are probably caused by electrostatic changes in the iron-fibrinogen system, though hydroxyl radical (OH˙) formation can also contribute under both acute and (more especially) chronic conditions. Many substances are known to affect the nature of fibrin polymerised from fibrinogen, such that this might be seen as a kind of bellwether for human or plasma health. Overall, our analysis demonstrates the commonalities underpinning a variety of pathologies as seen in both hypercoagulability and hypofibrinolysis, and offers opportunities for both diagnostics and therapies.

Global assays of hemostasis

PURPOSE OF REVIEW

There exists an imbalance between our understanding of the physiology of the blood coagulation process and the translation of this understanding into useful assays for clinical application. As technology advances, the capabilities for merging the two areas have become more attainable. Global assays have advanced our understanding of the dynamics of the blood coagulation process beyond end point assays and are at the forefront of implementation in the clinic.

RECENT FINDINGS

We will review recent advances in the main global assays with a focus on thrombin generation that have potential for clinical utility. These assays include direct (thrombogram, whole blood, purified systems) and indirect empirical measures of thrombin generation (thromboelastography) and mechanism-based computational models that use plasma composition data from individuals to generate thrombin generation profiles.

SUMMARY

Empirical thrombin generation assays (direct and indirect) and computational modeling of thrombin generation have greatly advanced our understanding of the hemostatic balance. Implementation of these types of assays and visualization approaches in the clinic will potentially provide a basis for the development of individualized patient care. Advances in both empirical and computational global assays have made the goal of predicting precrisis changes in an individual's hemostatic state one step closer.

Hypercoagulability detected by whole blood thromboelastometry (ROTEM®) and impedance aggregometry (MULTIPLATE®) in obese patients

INTRODUCTION

Obesity has been associated with hypercoagulability and to increased risk of both arterial and venous thromboembolic events. Many different and complex changes in plasma coagulation factors have been described in patients with obesity. The aim of this case-control study is to evaluate hypercoagulability in a group of overweight and obese subjects by whole blood rotation thromboelastometry (ROTEM®) and impedance aggregometry (Multiplate®).

METHODS

ROTEM® and Multiplate® analyses were performed in 80 subjects with a BMI ≥ 25 Kg/m(2), of whom 20 overweight [BMI = 25-29.9 Kg/m(2)], 20 with I degree obesity [BMI = 30-34.9 Kg/m(2)], 20 with II degree obesity [BMI = 35-39.9 Kg/m(2)] and 20 with III degree [BMI > 40 Kg/m(2)] and compared with 80 age and gender-matched normal weight healthy individuals.

RESULTS

Thromboelastometry. In INTEM and EXTEM tests MCF and AUC were significantly increased in III degree obese compared with controls. MCF in FIBTEM was significantly higher in I, II and III degree obesity than controls (p = 0.027, 0.002 and < 0.001, respectively). Impedance aggregometry. A significant difference in platelet aggregation was found between III degree obese subjects and healthy controls in each of the tests considered. A significant correlation between FIBTEM-MCF and aggregometry parameters with BMI, waist circumference, leptin levels and high sensitive-C reactive proteins was also found.

CONCLUSIONS

A relationship between hypercoagulability detected by whole blood thromboelastometry and aggregometry and increased fat mass is shown. Hypercoagulability also correlated with inflammatory markers. Point-of-care tests can be used to assess the degree of hypercoagulability and hyperaggregability in obese patients. Wider studies are needed to confirm our observations.

Complications following hepatectomy

As the number of liver resections in the United States has increased, operations are more commonly performed on older patients with multiple comorbidities. The advent of effective chemotherapy and techniques such as portal vein embolization, have compounded the number of increasingly complex resections taking up to 75% of healthy livers. Four potentially devastating complications of liver resection include postoperative hemorrhage, venous thromboembolism, bile leak, and post-hepatectomy liver failure. The risk factors and management of these complications are herein explored, stressing the importance of identifying preoperative factors that can decrease the risk for these potentially fatal complications.

Hematologic manifestations of liver disease

The liver plays a key role in both protein biosynthesis and lipid metabolism. As a result, hepatic synthetic dysfunction can have adverse effects on both cellular and soluble components of blood. Anemia may occur due to the hemolysis of acanthocytes (spur cells), which is ultimately due to abnormal lipid composition of the red blood cell membrane. Thrombocytopenia may result from several different mechanisms. Cytopenias also may be a consequence of hypersplenism. The liver is the primary site for synthesis of most procoagulant and anticoagulant proteins. The coagulopathy of liver disease is therefore complex. Early in the course of liver disease, thrombocytopenia and a coagulopathy associated with a prothrombotic state are not uncommon, whereas with more advanced disease pancytopenia and coagulopathy associated with hemorrhage become manifest. Fresh frozen plasma and adjuncts to hemostasis may be used as temporizing measures in bleeding patients. However, definitive management of many of the defects due to fulminant hepatic failure requires liver transplantation.

Pharmacologic prophylaxis, postoperative INR, and risk of venous thromboembolism after hepatectomy

INTRODUCTION

Pharmacologic prophylaxis (PP) is recommended for patients undergoing general surgical procedures with at least moderate risk of venous thromboembolism (VTE). The role of PP in patients undergoing hepatectomy is controversial, however, due to concerns regarding postoperative liver dysfunction and bleeding.

METHODS

We conducted a retrospective analysis of a prospectively maintained institutional database in order to clarify the relationship between PP, postoperative INR, and risk of VTE.

RESULTS

Postoperative VTE occurred in 55 of 2,147 patients (2.6 %) and was independently associated with advanced age, higher BMI, longer procedure time, and development of a major complication, as well as higher postoperative INR (≥1.5 versus <1.5: OR 2.50, P = 0.006). Patients undergoing more extensive liver resection with higher postoperative INR were less likely to receive PP, but receipt of PP demonstrated no relationship with either VTE incidence or hemorrhagic complications.

CONCLUSIONS

In this large single-institution study, incidence of VTE was not associated with PP but was associated with higher postoperative INR, contrary to the notion that postoperative liver dysfunction is protective against VTE. The interplay between prothrombotic and antithrombotic mechanisms in posthepatectomy patients must be more completely characterized before broad recommendations can be made regarding PP use in these patients.

Early Detection of Coagulation Abnormalities in Patients at Nutritional Risk: The Novel Role of Thromboelastography

It is believed that malnutrition is common among hospitalized patients and associated with increased risk of morbidity and mortality. It is unclear if it is more likely to cause coagulation disorders in patients with malnutrition. We, therefore, investigate the feasibility of using thromboelastography (TEG) in early detection of coagulation abnormalities in patients at nutritional risk. Fifty successive adult patients with gastrointestinal disease were prospectively divided into one of two groups according to nutritional risk score (less than 3 and 3 or greater). Blood samples were collected at admission for analysis of standard biochemical parameters, routine coagulation tests, and TEG parameters. A total of 62 per cent of patients (n = 31) were at nutritional risk. Serum concentrations of prealbumin, transferrin, total protein, low-density lipoprotein, high-density lipoprotein, and cholesterol were much lower in the nutritional risk group than in the no-risk group ( P ≤ 0.05). There was no significant difference in routine coagulation tests, whereas most of the TEG parameters showed significant differences between the two groups. The overall coagulation function was worse in patients at nutritional risk than in patients with good nutritional status ( P ≤ 0.01). TEG appears to be more sensitive for the detection of coagulation abnormalities compared with routine coagulation tests in patients at nutritional risk. The phenomenon described in this article should be useful in further studies of patients with malnutrition.

Use of global assays to understand clinical phenotype in congenital factor VII deficiency

Congenital factor VII (FVII) deficiency is characterized by genotypic variability and phenotypic heterogeneity. Traditional screening and factor assays are unable to reliably predict clinical bleeding phenotype and guide haemorrhage prevention strategy. Global assays of coagulation and fibrinolysis may better characterize overall haemostatic balance and aid in haemorrhagic risk assessment. We evaluated the ability of novel global assays to better understand clinical bleeding severity in congenital FVII deficiency. Subjects underwent central determination of factor VII activity (FVII:C) as well as clot formation and lysis (CloFAL) and simultaneous thrombin and plasmin generation (STP) global assay analysis. A bleeding score was assigned to each subject through medical chart review. Global assay parameters were analysed with respect to bleeding score and FVII:C. Subgroup analyses were performed on paediatric subjects and subjects with FVII ≥ 1 IU dL(-1). CloFAL fibrinolytic index (FI2 ) inversely correlated with FVII:C while CloFAL maximum amplitude (MA) and STP maximum velocity of thrombin generation (VT max) varied directly with FVII:C. CloFAL FI2 directly correlated with bleeding score among subjects in both the total cohort and paediatric subcohort, but not among subjects with FVII ≥ 1 IU dL(-1) . Among subjects with FVII ≥ 1 IU dL(-1), STP time to maximum velocity of thrombin generation and time to maximum velocity of plasmin generation inversely correlated with bleeding score. These preliminary findings suggest a novel potential link between a hyperfibrinolytic state in bleeding severity and congenital FVII deficiency, an observation that should be further explored.