Thrombosis: a major contributor to the global disease burden

Optimal utilization of thrombophilia testing

The global incidence of venous thromboembolism is high so laboratory testing for hereditary thrombophilia and selected acquired thrombophilia is common. Given the costs associated with testing and multiple pre-analytic and analytic variables affecting the assays, careful patient selection and timing of testing and diligent application to patient management are critical to providing high-value clinical care. Collaboration between the ordering providers and performing laboratories has the potential to achieve these goals. Herein, utility of thrombophilia testing, variables that affect the assays, and impact on patient management are reviewed. Where available, information on cost-effectiveness is discussed.

Antidepressants, Depression, and Venous Thromboembolism Risk: Large Prospective Study of UK Women

BACKGROUND

Some investigators have reported an excess risk of venous thromboembolism (VTE) associated with depression and with use of antidepressant drugs. We explored these associations in a large prospective study of UK women.

METHODS AND RESULTS

The Million Women Study recruited 1.3 million women through the National Health Service Breast Screening Programme in England and Scotland. Three years after recruitment, women were sent a second questionnaire that enquired about depression and regular use of medications in the previous 4 weeks. The present analysis included those who responded and did not have prior VTE, cancer, or recent surgery. Follow-up for VTE was through linkage to routinely collected National Health Service statistics. Cox regression analyses yielded adjusted hazard ratios and 95% CIs. A total of 734 092 women (mean age 59.9 years) were included in the analysis; 6.9% reported use of antidepressants, 2.7% reported use of other psychotropic drugs, and 1.8% reported being treated for depression or anxiety but not use of psychotropic drugs. During follow-up for an average of 7.3 years, 3922 women were hospitalized for and/or died from VTE. Women who reported antidepressant use had a significantly higher risk of VTE than women who reported neither depression nor use of psychotropic drugs (hazard ratio, 1.39; 95% CI, 1.23-1.56). VTE risk was not significantly increased in women who reported being treated for depression or anxiety but no use of antidepressants or other psychotropic drugs (hazard ratio, 1.19; 95% CI, 0.95-1.49).

CONCLUSIONS

Use of antidepressants is common in UK women and is associated with an increased risk of VTE.

Characterizing the relationship between age and venous thromboembolism in adult trauma patients: findings from the National Trauma Data Bank and the National Inpatient Sample

BACKGROUND

Venous thromboembolism (VTE) is a tremendous burden in health care. However, current guidelines lack recommendations regarding the prevention of VTE in older adult trauma patients. Furthermore, the appropriate method of modeling of age in VTE models is currently unclear.

METHODS

Patients included in the National Trauma Data Bank (NTDB) between the years 2008 and 2014 and patients included in the National Inpatient Sample (NIS) between 2009 and 2013 were analyzed. Multiple logistic regression of VTE on age was performed.

RESULTS

Of 3,598,881 patients in the NTDB, 34,202 (1.0%) were diagnosed with VTE compared to 5405 (1.1%) of the 505,231 patients in NIS. In both the fully adjusted NTDB and NIS model, age was positively associated with odds of VTE diagnosis under 65 years (NTDB, adjusted odds ratio [aOR]: 1.018, 95% confidence interval [CI]: 1.017-1.019, P < 0.001; NIS, aOR: 1.025, 95% CI 1.022-1.027, P < 0.001). In patients aged ≥65 years, age was negatively associated with odds of VTE diagnosis in the NTDB (aOR: 0.995, 95% CI: 0.992-0.999, P = 0.006) but not in the NIS (aOR: 0.998, 95% CI 0.994-1.002, P = 0.26).

CONCLUSIONS

Incidence of VTE among adult trauma patients steadily increases with age until 65 years, after which the odds of VTE appear to level off or even slightly decrease. These findings should be applied for improved modeling of VTE in trauma patients. The mechanism behind these findings should be explored before using them to update guidelines for standardized VTE prevention in older adults.

Global Burden of Thrombosis: Epidemiologic Aspects

Thromboembolic conditions were estimated to account for 1 in 4 deaths worldwide in 2010 and are the leading cause of mortality. Thromboembolic conditions are divided into arterial and venous thrombotic conditions. Ischemic heart disease and ischemic stroke comprise the major arterial thromboses and deep-vein thrombosis and pulmonary embolism comprise venous thromboembolism. Atrial fibrillation is a major risk factor for stroke and systemic arterial thromboembolism. Estimates of the global burden of disease were obtained from Global Burden of Disease Project reports, recent systematic reviews, and searching the published literature for recent studies reporting measures of incidence, burden, and disability-adjusted life-years. Estimates per 100 000 of the global incidence rate (IR) for each condition are ischemic heart disease, IR=1518.7; myocardial infarction, IR=139.3; ischemic stroke, IR=114.3; atrial fibrillation, IR=77.5 in males and 59.5 in females; and venous thromboembolism, IR=115 to 269. Mortality rates (MRs) for each condition are ischemic heart disease, MR=105.5; ischemic stroke, MR=42.3; atrial fibrillation, MR=1.7; and venous thromboembolism, MR=9.4 to 32.3. Global public awareness is substantially lower for pulmonary embolism (54%) and deep-vein thrombosis (44%) than heart attack (88%) and stroke (85%). Over time, the incidence and MRs of these conditions have improved in developed countries, but are increasing in developing countries. Public health efforts to measure disease burden and increase awareness of symptoms and risk factors need to improve, particularly in low- and middle-income regions to address this leading cause of morbidity and mortality.

Animal Models of Thrombosis From Zebrafish to Nonhuman Primates: Use in the Elucidation of New Pathologic Pathways and the Development of Antithrombotic Drugs

Thrombosis is a leading cause of morbidity and mortality worldwide. Animal models are used to understand the pathological pathways involved in thrombosis and to test the efficacy and safety of new antithrombotic drugs. In this review, we will first describe the central role a variety of animal models of thrombosis and hemostasis has played in the development of new antiplatelet and anticoagulant drugs. These include the widely used P2Y12 antagonists and the recently developed orally available anticoagulants that directly target factor Xa or thrombin. Next, we will describe the new players, such as polyphosphate, neutrophil extracellular traps, and microparticles, which have been shown to contribute to thrombosis in mouse models, particularly venous thrombosis models. Other mouse studies have demonstrated roles for the factor XIIa and factor XIa in thrombosis. This has spurred the development of strategies to reduce their levels or activities as a new approach for preventing thrombosis. Finally, we will discuss the emergence of zebrafish as a model to study thrombosis and its potential use in the discovery of novel factors involved in thrombosis and hemostasis. Animal models of thrombosis from zebrafish to nonhuman primates are vital in identifying pathological pathways of thrombosis that can be safely targeted with a minimal effect on hemostasis. Future studies should focus on understanding the different triggers of thrombosis and the best drugs to prevent each type of thrombotic event.

Exploring indications for the Use of direct oral anticoagulants and the associated risks of major bleeding

Thrombosis is a leading cause of morbidity and mortality in the United States. Arterial and venous thromboses are implicated in the pathogenesis of major disorders, including myocardial infarction, ischemic stroke, and venous thromboembolism. Over the past decade, direct oral anticoagulants (DOACs) (eg, direct thrombin inhibitor and factor Xa [FXa] inhibitors) have been adopted as alternatives to warfarin due to their clinical advantages and efficacy for the treatment of thrombosis. As with all anticoagulants, treatment with DOACs is associated with a risk of major bleeding, including life-threatening gastrointestinal bleeds and intracranial hemorrhages (ICHs). In turn, the burden of bleeding associated with DOAC treatment is itself associated with substantial healthcare costs that are amplified by an increased risk of thromboembolic events and mortality following major bleeding events, especially in patients with ICHs. Given the rapid adoption of the DOACs and projected usage in the large patient population affected by thromboembolic conditions, clinicians are increasingly likely to encounter patients with major bleeding events due to DOAC therapy. Unlike warfarin, effective strategies to manage these bleeds are limited. There is an unmet need for reversal agents for use in the management of patients who receive FXa inhibitors and experience life-threatening bleeding or need emergency surgery. Andexanet alfa and ciraparantag are being evaluated as potential antidotes for both direct and indirect FXa inhibitors.

Vehicle-dependent Effects of Sphingosine 1-phosphate on Plasminogen Activator Inhibitor-1 Expression

Aim: Sphingosine 1-phosphate (S1P) has been suggested to be a positive regulator of plasminogen activator inhibitor 1 (PAI-1) in adipocytes, while some studies are not consistent with this prothrombotic property of S1P. Since S1P is bound to apolipoprotein M (apoM) on HDL or to albumin in plasma, we compared the properties of these two forms on the PAI-1 induction.

Methods: We investigated the associations of S1P, apoM, and PAI-1 concentrations in the plasma of normal coronary artery (NCA), stable angina pectoris (SAP), and acute coronary syndrome (ACS) subjects (n = 32, 71, and 38, respectively). Then, we compared the effects of S1P with various vehicles on the PAI-1 expression in 3T3L1 adipocytes. We also investigated the modulation of the PAI-1 levels in mice infected with adenovirus coding apoM.

Results: Among ACS subjects, the PAI-1 level was positively correlated with the S1P level, but not the apoM level. In adipocytes, S1P bound to an apoM-rich vehicle induced PAI-1 expression to a lesser extent than the control vehicle, while S1P bound to an apoM-depleted vehicle induced PAI-1 expression to a greater extent than the control vehicle in 3T3L1 adipocytes. Additionally, apoM overexpression in mice failed to modulate the plasma PAI-1 level and the adipose PAI-1 expression level. S1P bound to albumin increased PAI-1 expression through the S1P receptor 2-Rho/ROCK-NFκB pathway.

Conclusion: S1P bound to albumin, but not to apoM, induces PAI-1 expression in adipocytes, indicating that S1P can exert different properties on the pathogenesis of vascular diseases, depending on its vehicle.

Whole Exome Sequencing Reveals Severe Thrombophilia in Acute Unprovoked Idiopathic Fatal Pulmonary Embolism

BACKGROUND

Acute unprovoked idiopathic fatal pulmonary embolism (IFPE) causes sudden death without an identifiable thrombogenic risk. We aimed to investigate the underlying genomic risks of IFPE through whole exome sequencing (WES).

METHODS

We reviewed 14years of consecutive out-of-hospital fatal pulmonary embolism records (n=1478) from the ethnically diverse population of New York City. We selected 68 qualifying IFPE cases for WES. We compared the WES data of IFPE cases to those of 9332 controls to determine if there is an excess of rare damaging variants in the genome using ethnicity-matched controls in collapsing analyses.

FINDINGS

We found nine of the 68 decedents (13·2%) who died of IFPE had at least one pathogenic or likely pathogenic variant in one of the three anti-coagulant genes: SERPINC1 (Antithrombin III), PROC, and PROS1. The odds ratio of developing IFPE as a variant carrier for SERPINC1 is 144·2 (95% CI, 26·3-779·4; P=1·7×10-7), for PROC is 85·6 (95% CI, 13·0-448·9; P=2.0×10-5), and for PROS1 is 56·4 (95% CI, 5·3-351·1; P=0·001). The average age-at-death of anti-coagulant gene variant carriers is significantly younger than that of non-carriers (28·56years versus 38·02years; P=0·01).

INTERPRETATION

This study showed the important role of severe thrombophilia due to natural anti-coagulant deficiency in IFPE. Evaluating severe thrombophilia in out-of-hospital fatal PE beyond IFPE is warranted.

Policies and practices in haemostasis testing among laboratories in Croatia: a survey on behalf of a Working Group for Laboratory Coagulation of the Croatian Society of Medical Biochemistry and Laboratory Medicine

INTRODUCTION

The objective of this survey was to assess current policies and practice in haemostasis testing among both hospital and outpatient laboratories in Republic of Croatia.

MATERIALS AND METHODS

A questionnaire with seventy questions divided into nine sections was created in May 2015. Participants were asked about their practice related to test request form, sample collection, prothrombin time (PT) and activated partial thromboplastin time assays, other individual haemostasis assays, point-of-care testing (POCT), reporting of coagulation tests results and quality assurance of procedures, the personnel and other laboratory resources, as well as on issues related to education and implementation of additional coagulation assays in their laboratory. The survey was administered and data were collected between June and September 2015.

RESULTS

A total survey response rate was 104/170 (61.2%). Most respondents were faced with incomplete information on prescribed therapy and diagnosis on the test request or inappropriate samples withdrawn on distant locations, but also do not have protocols for handling samples with high haematocrit values. Reporting of PT-INR and D-dimer results was different between laboratories. Although almost all laboratories developed a critical value reporting system, reporting a value to general practitioners is still a problem. Result on coagulation POCT testing showed that not all devices were supervised by laboratories, which is not in compliance with Croatian Chamber of Medical Biochemistry acts.

CONCLUSION

Obtained results highlighted areas that need improvement and different practice patterns in particular field of haemostasis testing among laboratories. A harmonization of the overall process of haemostasis testing at national level should be considered and undertaken.

Thromboprophylaxis after Knee Arthroscopy and Lower-Leg Casting

BACKGROUND

The use of thromboprophylaxis to prevent clinically apparent venous thromboembolism after knee arthroscopy or casting of the lower leg is disputed. We compared the incidence of symptomatic venous thromboembolism after these procedures between patients who received anticoagulant therapy and those who received no anticoagulant therapy.

METHODS

We conducted two parallel, pragmatic, multicenter, randomized, controlled, open-label trials with blinded outcome evaluation: the POT-KAST trial, which included patients undergoing knee arthroscopy, and the POT-CAST trial, which included patients treated with casting of the lower leg. Patients were assigned to receive either a prophylactic dose of low-molecular-weight heparin (for the 8 days after arthroscopy in the POT-KAST trial or during the full period of immobilization due to casting in the POT-CAST trial) or no anticoagulant therapy. The primary outcomes were the cumulative incidences of symptomatic venous thromboembolism and major bleeding within 3 months after the procedure.

RESULTS

In the POT-KAST trial, 1543 patients underwent randomization, of whom 1451 were included in the intention-to-treat population. Venous thromboembolism occurred in 5 of the 731 patients (0.7%) in the treatment group and in 3 of the 720 patients (0.4%) in the control group (relative risk, 1.6; 95% confidence interval [CI], 0.4 to 6.8; absolute difference in risk, 0.3 percentage points; 95% CI, -0.6 to 1.2). Major bleeding occurred in 1 patient (0.1%) in the treatment group and in 1 (0.1%) in the control group (absolute difference in risk, 0 percentage points; 95% CI, -0.6 to 0.7). In the POT-CAST trial, 1519 patients underwent randomization, of whom 1435 were included in the intention-to-treat population. Venous thromboembolism occurred in 10 of the 719 patients (1.4%) in the treatment group and in 13 of the 716 patients (1.8%) in the control group (relative risk, 0.8; 95% CI, 0.3 to 1.7; absolute difference in risk, -0.4 percentage points; 95% CI, -1.8 to 1.0). No major bleeding events occurred. In both trials, the most common adverse event was infection.

CONCLUSIONS

The results of our trials showed that prophylaxis with low-molecular-weight heparin for the 8 days after knee arthroscopy or during the full period of immobilization due to casting was not effective for the prevention of symptomatic venous thromboembolism. (Funded by the Netherlands Organization for Health Research and Development; POT-KAST and POT-CAST ClinicalTrials.gov numbers, NCT01542723 and NCT01542762 , respectively.).

New findings on venous thrombogenesis

Venous thrombosis (VT) is the third most common cause of cardiovascular death worldwide. Complications from VT and pulmonary embolism are the leading cause of lost disability-adjusted life years. Risks include genetic (e.g., non-O blood group, activated protein C resistance, hyperprothrombinemia) and acquired (e.g., age, surgery, cancer, pregnancy, immobilisation, female hormone use) factors. Pathophysiologic mechanisms that promote VT are incompletely understood, but involve abnormalities in blood coagulability, vessel function, and flow (so-called Virchow's Triad). Epidemiologic studies of humans, animal models, and biochemical and biophysical investigations have revealed contributions from extrinsic, intrinsic, and common pathways of coagulation, endothelial cells, leukocytes, red blood cells, platelets, cell-derived microvesicles, stasis-induced changes in vascular cells, and blood rheology. Knowledge of these mechanisms may yield new therapeutic targets. Characterisation of mechanisms that mediate VT formation and stability, particularly in aging, are needed to advance understanding of VT.

Cancer associated thrombosis: risk factors and outcomes

Deep vein thrombosis of the leg and pulmonary embolism are frequent diseases and cancer is one of their most important risk factors. Patients with cancer also have a higher prevalence of venous thrombosis located in other parts than in the legs and/or in unusual sites including upper extremity, splanchnic or cerebral veins. Cancer also affects the risk of arterial thrombotic events particularly in patients with myeloproliferative neoplasms and in vascular endothelial growth factor receptor inhibitor recipients. Several risk factors need to interact to trigger thrombosis. In addition to common risk factors such as surgery, hospitalisation, infection and genetic coagulation disorders, the thrombotic risk is also driven and modified by cancer-specific factors including type, histology, and stage of the malignancy, cancer treatment and certain biomarkers. A venous thrombotic event in a cancer patient has serious consequences as the risk of recurrent thrombosis, the risk of bleeding during anticoagulation and hospitalisation rates are all increased. Survival of cancer patients with thrombosis is worse compared to that of cancer patients without thrombosis, and thrombosis is a leading direct cause of death in cancer patients.

PDGFB, a new candidate plasma biomarker for venous thromboembolism: results from the VEREMA affinity proteomics study

High-throughput affinity plasma proteomic profiling can identify candidate plasma biomarkers for VTE. Elevated plasma PDGFB levels are identified as associated with VTE in 2 independent case control studies.

The Association between Residence Floor Level and Cardiovascular Disease: The Health and Environment in Oslo Study

Background. Increasingly more people live in tall buildings and on higher floor levels. Factors relating to floor level may protect against or cause cardiovascular disease (CVD). Only one previous study has investigated the association between floor level and CVD. Methods. We studied associations between floor of bedroom and self-reported history of stroke, venous thromboembolism (VTE), and intermittent claudication (IC) among 12.525 inhabitants in Oslo, Norway. We fitted multivariate logistic regression models and adjusted for sociodemographic variables, socioeconomic status (SES), and health behaviors. Additionally, we investigated block apartment residents (N = 5.374) separately. Results. Trend analyses showed that disease prevalence increased by floor level, for all three outcomes. When we investigated block apartment residents alone, the trends disappeared, but one association remained: higher odds of VTE history on 6th floor or higher, compared to basement and 1st floor (OR: 1.504; 95% CI: 1.007–2.247). Conclusion. Floor level is positively associated with CVD, in Oslo. The best-supported explanation may be residual confounding by building height and SES. Another explanation, about the impact of atmospheric electricity, is also presented. The results underline a need to better understand the associations between residence floor level and CVD and multistory housing and CVD.

RE-COVERY DVT/PE: Rationale and design of a prospective observational study of acute venous thromboembolism with a focus on dabigatran etexilate

The therapeutic management of venous thromboembolism (VTE) is rapidly evolving. Following the positive results of pivotal large-scale randomised trials, the non-vitamin K antagonist oral anticoagulants (NOACs) represent an important alternative to standard anticoagulation. In phase III studies, dabigatran was as effective as, and significantly safer than warfarin. Additional information on real-world data of dabigatran is now warranted. RE-COVERY DVT/PE is a multi-centre, international, observational (i. e. non-interventional) study enrolling patients with acute DVT and/or PE within 30 days after objective diagnosis. The study is designed with two phases. Phase 1 has a cross-sectional design, enrolling approximately 6000 patients independently of treatment choice, with the aim of providing a contemporary picture of the management of VTE worldwide. Phase 2 has a prospective cohort design, with follow-up of one year, enrolling 8000 patients treated with dabigatran or vitamin K antagonists (VKAs) with the aim of comparing their safety, defined by the occurrence of major bleeding, and effectiveness, defined by the occurrence of symptomatic recurrent VTE. RE-COVERY DVT/PE will complement both the results of other observational studies in this field and the results of phase III studies with dabigatran, in particular by assessing its clinical benefit in various patient subgroups treated in routine clinical practice.

Epidemiology and risk factors for venous thromboembolism in lung cancer

PURPOSE OF REVIEW

Cancer is a strong risk factor for venous thromboembolism (VTE). In patients with lung cancer VTE is a significant cause for morbidity and mortality. The purpose of the review is to summarize the epidemiology of thrombotic events, risk factors for VTE and the clinical impact of VTE in patients with lung cancer.

RECENT FINDINGS

The rates of VTE in lung cancer patients vary according to different types of investigations, and reach 7 to 13%, including a significant number of unsuspected pulmonary emboli. Risk factors for VTE in patients with lung cancer can be basically divided into three categories: patient, tumor, and treatment related. In addition, a number of biomarkers have been described to be associated with VTE risk (e.g., D-dimer).

SUMMARY

Knowledge about the epidemiology, risk factors, and prognostic value of VTE in lung cancer could help to prevent thrombotic complications and improve management of patients with lung cancer.

Autumn season birth is associated with a lower frequency of diagnosis of unprovoked deep vein thrombosis in the emergency department

A significant association was described between lifetime frequency of several human diseases, including cardiovascular disorders, and birth season. We performed a retrospective study to establish whether an association exists between birth season and frequency of venous thromboembolism diagnosed in the emergency department. The study population consisted of all consecutive patients diagnosed with venous thromboembolism at the emergency department of the University Hospital of Parma (Italy) during the year 2014. A total number of 400 patients (217 women and 183 men; mean age 70 ± 18 years) received a final diagnosis of venous thromboembolism throughout the study period. The lowest frequency of diagnoses was observed in patients born in autumn, whereas a higher frequency was observed in those born in spring or summer. When compared with the frequency of births in the same geographical area, patients born in spring and summer exhibited a 30 and 25% higher risk of venous thromboembolism compared with those having autumn birth. A similar trend was observed in patients with unprovoked thrombosis, but not in those with provoked thrombosis. A subanalysis of patients with unprovoked deep vein thrombosis revealed that both spring birth (relative risk 1.49, 95% confidence interval 1.04-2.14) and summer birth (relative risk 1.46, 95% confidence interval 1.01-2.09) were significant risk factors for this condition compared with autumn birth. Although further studies are needed to confirm these original findings, it seems reasonable to hypothesize that birth season may influence the lifetime risk of venous thromboembolism, especially of unprovoked deep vein thrombosis.

Causes of venous thrombosis

Venous thrombosis which mainly manifests as deep vein thrombosis of the leg or pulmonary embolism occurs in 1 per 1000 per year. It occurs due to interacting genetic, environmental and behavioral risk factors. The strongest risk factors are certain types of surgery and malignancies. Over the last decade many new risk factors for venous thrombosis have been identified. Venous thrombosis has a high recurrence rate, of around 5 % per year. Whereas clinically it would be most important to identify patients at risk of recurrence, only male sex and a previous unprovoked thrombosis are established determinants of recurrent thrombosis.

Tetrahydroisoquinolines in therapeutics: a patent review (2010-2015)

INTRODUCTION

1,2,3,4-Tetrahydroisoquinoline (THIQ) is one of the 'privileged scaffolds', commonly found in nature. Initially, this class of compounds was known for its neurotoxicity. Later on, 1-methyl-1,2,3,4-tetrahydroisoquinoline was proved as an endogeneous Parkinsonism-preventing agent in mammals. The fused THIQs have been studied for their role as anticancer antibiotics. The US FDA approval of the trabectedin for the treatment of soft tissue sarcomas, is a milestone in the anticancer drug discovery. Areas covered: This review covers the patents on various therapeutic activities of the THIQ derivatives in the years between 2010 and 2015. Patents were collected using a thorough search of Espacenet and WIPO databases. The therapeutic areas covered include cancer, malaria, central nervous system (CNS), cardiovascular, metabolic disorders, and so on. This also includes several patents on specific THIQs of clinical importance. Expert opinion: A large number of the THIQ derivatives have been synthesised for various therapeutic activities, with noticeable success in the area of drug discovery for cancer and CNS. They may also prove to be promising candidates for various infectious diseases, such as malaria, tuberculosis, HIV-infection, HSV-infection, leishmaniasis, etc. They can also be developed as novel class of drugs for various therapeutic activities with unique mechanism of action.

Edoxaban: A Review in Deep Vein Thrombosis and Pulmonary Embolism

Edoxaban (Lixiana, Savaysa) is an oral, direct factor Xa inhibitor which has recently been approved for use in the treatment of deep vein thrombosis (DVT) and pulmonary embolism (PE) [collectively, venous thromboembolism (VTE)] and for the prevention of recurrent VTE. This article reviews the pharmacological properties of edoxaban as well as its tolerability and therapeutic efficacy in the treatment and prevention of recurrent VTE events. As demonstrated in the pivotal Hokusai-VTE phase III trial, once-daily edoxaban after initial treatment with heparin was non-inferior to standard therapy with heparin/warfarin in preventing recurrent VTE events and was associated with a significantly lower risk of clinically relevant bleeding than the traditional therapy. Edoxaban shares the advantages of other direct oral anticoagulants (DOACs) over traditional therapies, including the lack of requirement for routine coagulation monitoring, a rapid onset and offset of action, and few drug-drug interactions. It offers the convenience of once-daily dosing, can be taken without regard to food and allows for a dose reduction in patients with certain clinical features, such as moderate renal impairment or low body weight. In conclusion, edoxaban represents an effective and potentially safer alternative to traditional vitamin K antagonist therapy for the treatment and prevention of recurrent VTE. Its recent approval expands the range of DOAC agents for recurrent VTE, further facilitating treatment individualization.

Epidemiology of venous thromboembolism in the Framingham Heart Study

BACKGROUND

Reports of the crude incidence of venous thromboembolism (VTE) in Western countries vary widely. Data regarding risk factors, incidence and recurrence of VTE from deeply-phenotyped community-based cohort studies are needed.

OBJECTIVES

To study the incidence, associated mortality, and predisposing factors of VTE in the prospective, longitudinal community-based Framingham Heart Study.

PATIENTS/METHODS

The study sample consisted of the Framingham Heart Study Original, Offspring, Third Generation, and Omni cohorts (N=9754). Incidence rates (IR) were standardized to the 2000 US population. Cox proportional hazards regression models were used to study risk factor associations.

RESULTS

During 1995-2014 (total follow-up time 104,091 person-years [median 9.8 (range 0-20) years]), 297 incident VTE events were observed. Age-adjusted IR of VTE was 20.3/10,000 (95% CI 17.9-22.6). Of the events 120 (40%) were pulmonary embolism (PE) and 177 (60%) were deep venous thrombosis (DVT); 29% were unprovoked, 40% provoked, and 31% cancer-related. Cancer-related VTE was associated with high mortality at 30days (24.2%), 1year (66.3%), and 5years (75.6%). In multivariable models, age and obesity, but no other traditional cardiovascular risk factors, were significantly associated with VTE (hazard ratio [HR] per 10-year increase in age 1.69, 95% CI 1.48-1.92; HR for obesity (BMI≥30kg/m(2)) 1.88, 95% CI 1.44-2.45).

CONCLUSIONS

We provide data on the epidemiology of VTE. VTE is associated with significant mortality, and prognosis after cancer-related VTE is particularly poor. Traditional cardiovascular risk factors beyond age and obesity are not associated with VTE.

Pharmacology of Heparin and Related Drugs

Heparin has been recognized as a valuable anticoagulant and antithrombotic for several decades and is still widely used in clinical practice for a variety of indications. The anticoagulant activity of heparin is mainly attributable to the action of a specific pentasaccharide sequence that acts in concert with antithrombin, a plasma coagulation factor inhibitor. This observation has led to the development of synthetic heparin mimetics for clinical use. However, it is increasingly recognized that heparin has many other pharmacological properties, including but not limited to antiviral, anti-inflammatory, and antimetastatic actions. Many of these activities are independent of its anticoagulant activity, although the mechanisms of these other activities are currently less well defined. Nonetheless, heparin is being exploited for clinical uses beyond anticoagulation and developed for a wide range of clinical disorders. This article provides a "state of the art" review of our current understanding of the pharmacology of heparin and related drugs and an overview of the status of development of such drugs.

Allosteric Inhibition of Factor XIIIa. Non-Saccharide Glycosaminoglycan Mimetics, but Not Glycosaminoglycans, Exhibit Promising Inhibition Profile

Factor XIIIa (FXIIIa) is a transglutaminase that catalyzes the last step in the coagulation process. Orthostery is the only approach that has been exploited to design FXIIIa inhibitors. Yet, allosteric inhibition of FXIIIa is a paradigm that may offer a key advantage of controlled inhibition over orthosteric inhibition. Such an approach is likely to lead to novel FXIIIa inhibitors that do not carry bleeding risks. We reasoned that targeting a collection of basic amino acid residues distant from FXIIIa’s active site by using sulfated glycosaminoglycans (GAGs) or non-saccharide GAG mimetics (NSGMs) would lead to the discovery of the first allosteric FXIIIa inhibitors. We tested a library of 22 variably sulfated GAGs and NSGMs against human FXIIIa to discover promising hits. Interestingly, although some GAGs bound to FXIIIa better than NSGMs, no GAG displayed any inhibition. An undecasulfated quercetin analog was found to inhibit FXIIIa with reasonable potency (efficacy of 98%). Michaelis-Menten kinetic studies revealed an allosteric mechanism of inhibition. Fluorescence studies confirmed close correspondence between binding affinity and inhibition potency, as expected for an allosteric process. The inhibitor was reversible and at least 9-fold- and 26-fold selective over two GAG-binding proteins factor Xa (efficacy of 71%) and thrombin, respectively, and at least 27-fold selective over a cysteine protease papain. The inhibitor also inhibited the FXIIIa-mediated polymerization of fibrin in vitro. Overall, our work presents the proof-of-principle that FXIIIa can be allosterically modulated by sulfated non-saccharide agents much smaller than GAGs, which should enable the design of selective and safe anticoagulants.

Thrombosis in Cancer: Research Priorities Identified by a National Cancer Institute/National Heart, Lung, and Blood Institute Strategic Working Group

The risk for venous thromboembolism (VTE) is increased in cancer and particularly with chemotherapy, and it portends poorer survival among patients with cancer. However, many fundamental questions about cancer-associated VTE, or Trousseau syndrome, remain unanswered. This report summarizes the proceedings of a working group assembled by the NCI and NHLBI in August 2014 to explore the state of the science in cancer-associated VTE, identify clinically important research gaps, and develop consensus on priorities for future research. Representing a convergence of research priorities between the two NIH Institutes, the workshop addressed epidemiologic, basic science, clinical, and translational issues in cancer-associated VTE. Cancer Res; 76(13); 3671-5. ©2016 AACR.

Platelet-Monocyte Aggregates and C-Reactive Protein are Associated with VTE in Older Surgical Patients

Emerging evidence implicates platelets as key mediators of venous thromboembolism (VTE). Nevertheless, the pathways by which platelets and circulating procoagulant proteins synergistically orchestrate VTE remain incompletely understood. We prospectively determined whether activated platelets and systemic procoagulant factors were associated with VTE in 32 older orthopedic surgery patients. Circulating platelet-monocyte aggregates (PMAs), p-selectin expression (P-SEL), and integrin αIIbβ3 activation (PAC-1 binding) were assessed pre-operatively and 24 hours post-operatively. The proinflammatory and procoagulant molecule C-reactive protein (CRP), which induces PMA formation in vitro, along with plasma d-dimer and fibrinogen levels were also measured. The primary outcome was VTE occurring within 30 days post-operatively. Overall, 40.6% of patients developed VTE. Patients with VTE had a significant increase in circulating PMAs and CRP post-operatively, compared to those without VTE. Changes in PMA and CRP in VTE patients were significantly correlated (r² = 0.536, p = 0.004). In contrast, P-SEL expression and PAC-1 binding, fibrinogen levels, and d-dimers were not associated with VTE. This is the first study to identify that increased circulating PMAs and CRP levels are early markers associated with post-surgical VTE. Our findings also provide new clinical evidence supporting the interplay between PMAs and CRP in patients with VTE.

Chronic miR-29 antagonism promotes favorable plaque remodeling in atherosclerotic mice

Abnormal remodeling of atherosclerotic plaques can lead to rupture, acute myocardial infarction, and death. Enhancement of plaque extracellular matrix (ECM) may improve plaque morphology and stabilize lesions. Here, we demonstrate that chronic administration of LNA‐miR‐29 into an atherosclerotic mouse model improves indices of plaque morphology. This occurs due to upregulation of miR‐29 target genes of the ECM (col1A and col3A) resulting in reduced lesion size, enhanced fibrous cap thickness, and reduced necrotic zones. Sustained LNA‐miR‐29 treatment did not affect circulating lipids, blood chemistry, or ECM of solid organs including liver, lung, kidney, spleen, or heart. Collectively, these data support the idea that antagonizing miR‐29 may promote beneficial plaque remodeling as an independent approach to stabilize vulnerable atherosclerotic lesions.

Profile and anticoagulation outcomes of patients on warfarin therapy in an urban hospital in Cape Town, South Africa

BACKGROUND

Warfarin is the most frequently used oral anticoagulant worldwide and it is the oral anticoagulant of choice in South Africa for reducing thrombosis-related morbidity and mortality. However, the safety and efficacy of warfarin therapy depends mainly on careful monitoring and maintenance of the international normalised ratio (INR) within an optimal therapeutic range.

AIM

The aim of this study was to describe the profile and the anticoagulation outcomes of patients on warfarin therapy in a major warfarin clinic in the Western Cape Province of South Africa.

SETTING

Victoria Hospital - a district hospital in Cape Town.

METHODS

A cross sectional review of clinical records of patients on warfarin therapy who attended the INR clinic from 01 January 2014 to 30 June 2014 was done. Data analysis was done with STATA to generate appropriate descriptive data.

RESULTS

Our study showed that atrial fibrillation (AF) was the commonest indication for warfarin use in this study and hypertension was the commonest comorbidity among these patients. Only 48.5% achieved target therapeutic range; 51.5% were out-of-range. There was a significant association between alcohol consumption and poor anticoagulation outcomes (p-value < 0.022). Anticoagulation outcomes were better among the older age groups, male patients and in those with AF. The prevalence of thrombotic events while on warfarin treatment was 2.2%, while prevalence of haemorrhagic events was 14%. Most of the patients with bleeding events were on concurrent use of warfarin and other medications with potential drug interactions.

CONCLUSION

In our study, patients who achieved target therapeutic control were less than the acceptable 60%.

Use of decision aids for shared decision making in venous thromboembolism: A systematic review

BACKGROUND

Optimal care of patients with venous thromboembolism requires the input of patient preferences into clinical decision-making. However, the availability and impact of decision aids to facilitate shared decision making in care of venous thromboembolism is not well known.

OBJECTIVES

To assess the availability, clinical impact and outcomes associated with the use of decision aids in patients with or at risk for venous thromboembolism.

PATIENTS/METHODS

A systematic review of the literature was performed exploring the use of decision aids in patients with venous thromboembolism. Criteria for primary inclusion required use of patient values clarification in the decision aid. A secondary review without the requirement of a patient values clarification was performed to be more inclusive. The data was summarized such that knowledge gaps and opportunities for enquiry were identified.

RESULTS

The primary review identified one study that explored the decision to extend anticoagulation in patients with a recent venous thromboembolism beyond the stipulated 3-month duration. The secondary review identified an additional study exploring the decision to undergo computer tomography testing in patients at low risk for pulmonary embolism in an emergency department setting. Both studies were of modest quality given a lack of control group for comparison analysis.

CONCLUSIONS

Despite numerous calls to increase use of shared decision-making, a paucity of data exists to help patients engage in the treatment decisions for venous thromboembolism. Future studies of additional VTE clinical decisions with longer-term clinical outcomes appear necessary.

Founder effect is responsible for the p.Leu131Phe heparin-binding-site antithrombin mutation common in Hungary: phenotype analysis in a large cohort

BACKGROUND

Antithrombin (AT) is a key regulator of the coagulation. In type II deficiency, the heparin-binding-site defect (type II HBS) is considered to be relatively low thrombosis risk.

OBJECTIVES

Our aims were to search for SERPINC1 mutation(s) and to describe the clinical and laboratory phenotype of a large number of AT Budapest3 (ATBp3, p.Leu131Phe) carriers and confirm the presence of a founder effect.

PATIENTS/METHODS

AT-deficient patients were recruited and carriers of ATBp3, n = 102 (63 families) were selected. To investigate the founder effect, eight intragenic single nucleotide polymorphisms, a 5'-length dimorphism, and five microsatellite markers were detected. Clinical and laboratory data of the patients were collected and analyzed.

RESULTS

In AT deficiency, 16 different causative mutations were found, and the great majority of patients were of type II HBS subtype. Most of them (n = 102/118, 86.5%) carried the ATBp3 mutation. The ATBp3 mutant allele was associated with one single haplotype, while different haplotypes were detected in the case of normal allele. The anti-factor Xa-based AT activity assay that we used could detect all ATBp3 patients with high sensitivity in our cohort. ATBp3 homozygosity (n = 26) was associated with thrombosis at a young age and conferred a high thrombotic risk. Half of the heterozygotes (n = 41/76, 53.9%) also had venous and/or arterial thrombosis, and pregnancy complications were also recorded.

CONCLUSION

In Hungary, the founder mutation, ATBp3, is the most common AT deficiency. Our study is the first in which the clinical characterization of ATBp3 mutation was executed in a large population.

Measurement of microparticle tissue factor activity in clinical samples: A summary of two tissue factor-dependent FXa generation assays

Thrombosis is a leading cause of morbidity and mortality. Detection of a prothrombotic state using biomarkers would be of great benefit to identify patients at risk of thrombosis that would benefit from thromboprophylaxis. Tissue factor (TF) is a highly procoagulant protein that under normal conditions is not present in the blood. However, increased levels of TF in the blood in the form of microparticles (MPs) (also called extracellular vesicles) are observed under various pathological conditions. In this review, we will discuss studies that have measured MP-TF activity in a variety of diseases using two similar FXa generation assay. One of the most robust signals for MP-TF activity (16-26 fold higher than healthy controls) is observed in pancreatic cancer patients with venous thromboembolism. In this case, the TF+ MPs appear to be derived from the cancer cells. Surprisingly, cirrhosis and acute liver injury are associated with 17-fold and 38-fold increases in MP-TF activity, respectively. Based on mouse models, we speculate that the TF+ MPs are derived from hepatocytes. More modest increases are observed in patients with urinary tract infections (6-fold) and in a human endotoxemia model (9-fold) where monocytes are the likely source of the TF+ MPs. Finally, there is no increase in MP-TF activity in the majority of cardiovascular disease patients. These studies indicate that MP-TF activity may be a useful biomarker to identify patients with particular diseases that have an increased risk of thrombosis.

The MARINER trial of rivaroxaban after hospital discharge for medical patients at high risk of VTE. Design, rationale, and clinical implications

Hospital-associated venous thromboembolism (VTE) is a leading cause of premature death and disability worldwide. Evidence-based guidelines recommend that anticoagulant thromboprophylaxis be given to hospitalised medical patients at risk of VTE, but suggest against routine use of thromboprophylaxis beyond the hospital stay. The MARINER study is a randomised, double-blind, placebo-controlled trial to evaluate the efficacy and safety of thromboprophylaxis using rivaroxaban, begun at hospital discharge and continued for 45 days, for preventing symptomatic VTE in high-risk medical patients. Eligible patients are identified using the International Medical Prevention Registry on Venous Thromboembolism (IMPROVE VTE) risk score, combined with a laboratory test, D-dimer. The rivaroxaban regimen is 10 mg once daily for patients with CrCl ≥ 50 ml/min, or 7.5 mg once daily for patients with CrCl ≥ 30 ml/min and < 50 ml/min. The primary efficacy outcome is the composite of symptomatic VTE (lower extremity deep-vein thrombosis and non-fatal pulmonary embolism) and VTE-related death. The principal safety outcome is major bleeding. A blinded clinical events committee adjudicates all suspected outcome events. The sample size is event-driven with an estimated total of 8,000 patients to acquire 161 primary outcome events. Study design features that distinguish MARINER from previous and ongoing thromboprophylaxis trials in medically ill patients are: (i) use of a validated risk assessment model (IMPROVE VTE) and D-dimer determination for identifying eligible patients at high risk of VTE, (ii) randomisation at the time of hospital discharge, (iii) a 45-day treatment period and (iv) restriction of the primary efficacy outcome to symptomatic VTE events.

Venous thromboembolism in Latin America: a review and guide to diagnosis and treatment for primary care

There are various region-specific challenges to the diagnosis and effective treatment of venous thromboembolism in Latin America. Clear guidance for physicians and patient education could improve adherence to existing guidelines. This review examines available information on the burden of pulmonary embolism and deep vein thrombosis in Latin America and the regional issues surrounding the diagnosis and treatment of pulmonary embolism and deep vein thrombosis. Potential barriers to appropriate care, as well as treatment options and limitations on their use, are discussed. Finally, an algorithmic approach to the diagnosis and treatment of venous thromboembolism in ambulatory patients is proposed and care pathways for patients with pulmonary embolism and deep vein thrombosis are outlined for primary care providers in Latin America.

Heart failure and risk of venous thromboembolism: a systematic review and meta-analysis

BACKGROUND

Venous thromboembolism is a major global health problem that is often secondary to other clinical situations. Many studies have investigated the association between venous thromboembolism and heart failure, but have yielded inconsistent findings. We aimed to quantify the absolute and relative risks (RR) for venous thromboembolism in patients with heart failure after hospital admission. We also assessed rates of venous thromboembolism in patients in different settings.

METHODS

In this systematic review and meta-analysis, we searched for studies investigating the risk of venous thromboembolism in patients in hospital with heart failure. We searched for studies published between Jan 1, 1955, and March 31, 2015, in PubMed, Embase, Evidence-Based Medicine Reviews, Allied and Complementary Medicine Database, Ovid HealthSTAR, Global Health, Ovid Nursing Database, Web of Science, CINAHL Plus, ProQuest Central, Conference Papers Index, BIOSIS Previews, and ClinicalTrials.gov. All cohort studies and subgroup analyses of randomised controlled trials (RCTs) were eligible for inclusion if they reported venous thromboembolism rates (number of events per follow-up period) or RR estimates. We extracted data from published reports and contacted the corresponding authors of records with insufficient quantitative data. RRs and 95% CIs were pooled using a random-effects model. This study is registered with PROSPERO, number CRD42014015504.

FINDINGS

Of 8673 records identified, we included 71 studies with data from 88 cohorts in our analysis, with 59 cohorts included in the assessment of venous thromboembolism rates and 46 cohorts included in the meta-analysis of heart failure and risk of venous thromboembolism. Venous thromboembolism rates varied widely in patients in hospital with heart failure from different settings. The overall median symptomatic venous thromboembolism rate was 2·48% (IQR 0·84-5·61); rates was were 3·73% (1·05-7·31) for patients who did not receive thromboprophylaxis and 1·47% (0·64-3·54) for those who did. Overall, patients with heart failure in hospital had an RR of 1·51 (1·36-1·68) for venous thromboembolism. The overall I(2) statistic was 96·1% and there was no evidence of publication bias (Egger's test, p=0·46).

INTERPRETATION

Heart failure is a common independent risk factor for venous thromboembolism. Thromoboprophylaxis should be considered in clinical practice for high-risk patients.

FUNDING

National Natural Science Foundation.

Advances in our understanding of mechanisms of venous thrombus resolution

Traditionally, venous thrombosis has been seen as the consequence of a regulated cascade of proteolytic steps leading to the polymerization of fibrinogen and fibrin crosslinking that is facilitated by platelets. A new view of thrombosis is providing a more integrated concept, with components of the vascular wall contributing to the vascular remodeling of thrombosis. Angiogenesis and inflammation are two key mechanisms that safeguard venous thrombus resolution and restitution of vascular patency after thrombosis. Disturbance of these processes leads to thrombus persistence and has potentially severe consequences for affected patients. Examples for clinical conditions associated with recurrent or persisting venous thrombosis are post-thrombotic syndrome or chronic thromboembolic pulmonary hypertension. Recently, studies using animal models of venous thrombosis have contributed to a better understanding of thrombus non-resolution that will eventually lead to modification of current treatment concepts. For example, recent data suggest that innate immunity is involved in the modification of thrombosis.

The economic burden of incident venous thromboembolism in the United States: A review of estimated attributable healthcare costs

Venous thromboembolism (VTE), which includes deep vein thrombosis and pulmonary embolism, is an important cause of preventable mortality and morbidity. In this study, we summarize estimates of per-patient and aggregate medical costs or expenditures attributable to incident VTE in the United States. Per-patient estimates of incremental costs can be calculated as the difference in costs between patients with and without an event after controlling for differences in underlying health status. We identified estimates of the incremental per-patient costs of acute VTEs and VTE-related complications, including recurrent VTE, post-thrombotic syndrome, chronic thromboembolic pulmonary hypertension, and anticoagulation-related adverse drug events. Based on the studies identified, treatment of an acute VTE on average appears to be associated with incremental direct medical costs of $12,000 to $15,000 (2014 US dollars) among first-year survivors, controlling for risk factors. Subsequent complications are conservatively estimated to increase cumulative costs to $18,000-23,000 per incident case. Annual incident VTE events conservatively cost the US healthcare system $7-10 billion each year for 375,000 to 425,000 newly diagnosed, medically treated incident VTE cases. Future studies should track long-term costs for cohorts of people with incident VTE, control for comorbid conditions that have been shown to be associated with VTE, and estimate incremental medical costs for people with VTE who do not survive. The costs associated with treating VTE can be used to assess the potential economic benefit and cost-savings from prevention efforts, although costs will vary among different patient groups.

Kinetics and mechanics of clot contraction are governed by the molecular and cellular composition of the blood

Platelet-driven blood clot contraction (retraction) is thought to promote wound closure and secure hemostasis while preventing vascular occlusion. Notwithstanding its importance, clot contraction remains a poorly understood process, partially because of the lack of methodology to quantify its dynamics and requirements. We used a novel automated optical analyzer to continuously track in vitro changes in the size of contracting clots in whole blood and in variously reconstituted samples. Kinetics of contraction was complemented with dynamic rheometry to characterize the viscoelasticity of contracting clots. This combined approach enabled investigation of the coordinated mechanistic impact of platelets, including nonmuscle myosin II, red blood cells (RBCs), fibrin(ogen), factor XIIIa (FXIIIa), and thrombin on the kinetics and mechanics of the contraction process. Clot contraction is composed of 3 sequential phases, each characterized by a distinct rate constant. Thrombin, Ca(2+), the integrin αIIbβ3, myosin IIa, FXIIIa cross-linking, and platelet count all promote 1 or more phases of the clot contraction process. In contrast, RBCs impair contraction and reduce elasticity, while increasing the overall contractile stress generated by the platelet-fibrin meshwork. A better understanding of the mechanisms by which blood cells, fibrin(ogen), and platelet-fibrin interactions modulate clot contraction may generate novel approaches to reveal and to manage thrombosis and hemostatic disorders.

Global public awareness of venous thromboembolism

BACKGROUND

Data on public awareness about thrombosis in general and venous thromboembolism (VTE) in particular are limited. We aimed to measure the global awareness of thrombosis to address this gap.

METHODS

With Ipsos-Reid, from 22 July to 5 August 2014, we surveyed 800 respondents in their native language from each of Argentina, Australia, Canada, Germany, Japan, Thailand, the Netherlands, the United Kingdom and the United States to measure general awareness about thrombosis, including deep vein thrombosis (DVT) and pulmonary embolism (PE). In each country, respondents were distributed among three age groups: 18-39 years, 40-64 years, and over 65 years of age. Proportions and 95% confidence intervals (CIs) were calculated.

RESULTS

Overall, the proportion of respondents that were aware of thrombosis, DVT and PE (68%, 44% and 54%, respectively) was lower than the proportion that was aware of other thrombotic disorders, such as heart attack and stroke (88% and 85%, respectively), and health conditions such as hypertension, breast cancer, prostate cancer and AIDS (90%, 85%, 82% and 87%, respectively). Although there was variation across countries, lower awareness was associated with younger age and being male. Only 45% (95% CI, 43.9-46.5) of respondents were aware that blood clots were preventable, and awareness of cancer, hospitalization and surgery as risk factors was low (16%, 25%, and 36%, respectively).

CONCLUSIONS

On a global level, public awareness about thrombosis overall, and VTE in particular, is low. Campaigns to increase public awareness about VTE are needed to reduce the burden from this largely preventable thrombotic disorder.

Epidemiology of venous thromboembolism

Thrombosis can affect any venous circulation. Venous thromboembolism (VTE) includes deep-vein thrombosis of the leg or pelvis, and its complication, pulmonary embolism. VTE is a fairly common disease, particularly in older age, and is associated with reduced survival, substantial health-care costs, and a high rate of recurrence. VTE is a complex (multifactorial) disease, involving interactions between acquired or inherited predispositions to thrombosis and various risk factors. Major risk factors for incident VTE include hospitalization for surgery or acute illness, active cancer, neurological disease with leg paresis, nursing-home confinement, trauma or fracture, superficial vein thrombosis, and-in women-pregnancy and puerperium, oral contraception, and hormone therapy. Although independent risk factors for incident VTE and predictors of VTE recurrence have been identified, and effective primary and secondary prophylaxis is available, the occurrence of VTE seems to be fairly constant, or even increasing.

Venous thrombosis

Venous thromboembolism (VTE) encompasses deep-vein thrombosis (DVT) and pulmonary embolism. VTE is the leading cause of lost disability-adjusted life years and the third leading cause of cardiovascular death in the world. DVT leads to post-thrombotic syndrome, whereas pulmonary embolism can cause chronic pulmonary hypertension, both of which reduce quality of life. Genetic and acquired risk factors for thrombosis include non-O blood groups, factor V Leiden mutation, oral contraceptive use, hormone replacement therapy, advanced age, surgery, hospitalization and long-haul travel. A combination of blood stasis, plasma hypercoagulability and endothelial dysfunction is thought to trigger thrombosis, which starts most often in the valve pockets of large veins. Animal studies have revealed pathogenic roles for leukocytes, platelets, tissue factor-positive microvesicles, neutrophil extracellular traps and factors XI and XII. Diagnosis of VTE requires testing and exclusion of other pathologies, and typically involves laboratory measures (such as D-dimer) and diagnostic imaging. VTE is treated with anticoagulants and occasionally with thrombolytics to prevent thrombus extension and to reduce thrombus size. Anticoagulants are also used to reduce recurrence. New therapies with improved safety profiles are needed to prevent and treat venous thrombosis. For an illustrated summary of this Primer, visit: http://go.nature.com/8ZyCuY.