Incidence of venous thromboembolism in asymptomatic family members who are carriers of factor V Leiden: a prospective cohort study

Dilated superior ophthalmic vein: systemic associations

PURPOSE

To review systemic associations of patients with dilated superior ophthalmic veins (SOV) in the absence of orbital, cavernous sinus, or neurological disease.

METHODS

Retrospective review of patients who had dilated SOVs with a diameter of ≥ 5.0 mm. Patients with a dilated SOV secondary to orbital, cavernous sinus or neurological disease were excluded. Patient demographics, past medical history, and SOV diameters on initial and follow up scans were collected. The maximum diameter of the SOV was taken perpendicular to the long axis of the SOV.

RESULTS

Nine cases were identified. Patients ranged in age from 58 to 89 years and six out of nine were female. The dilated SOV involved both eyes in two cases, left eye in five cases and right eye in two cases. Three patients had dilated SOV likely secondary to raised venous pressures from decompensated right heart failure (n = 1), pericardial effusion (n = 1) and left ventricle dysfunction secondary to a myocardial infarction (n = 1). Five patients had a significant history of previous ischaemic heart or peripheral vascular disease. Two patients had risk factors for venous clotting disease whilst one patient had a history of giant cell arteritis and vertebral artery dissection.

CONCLUSION

A dilated SOV may raise concern for life threatening conditions such as a carotid cavernous fistula and may prompt additional investigations. A dilated SOV may be reversible and secondary to raised venous pressures due to cardiac failure. Other cases may be seen in patients with significant cardiovascular risk factors, possibly due to changes in vasculature.

Prediction of primary venous thromboembolism based on clinical and genetic factors within the U.K. Biobank

Both clinical and genetic factors drive the risk of venous thromboembolism. However, whether clinically recorded risk factors and genetic variants can be combined into a clinically applicable predictive score remains unknown. Using Cox proportional-hazard models, we analyzed the association of risk factors with the likelihood of venous thromboembolism in U.K. Biobank, a large prospective cohort. We then created a polygenic risk score of 36 single nucleotide polymorphisms and a clinical score determined by age, sex, body mass index, previous cancer diagnosis, smoking status, and fracture in the last 5 years. Participants were at significantly increased risk of venous thromboembolism if they were at high clinical risk (subhazard ratio, 4.37 [95% CI, 3.85-4.97]) or high genetic risk (subhazard ratio, 3.02 [95% CI, 2.63-3.47]) relative to participants at low clinical or genetic risk, respectively. The combined model, consisting of clinical and genetic components, was significantly better than either the clinical or the genetic model alone (P < 0.001). Participants at high risk in the combined score had nearly an eightfold increased risk of venous thromboembolism relative to participants at low risk (subhazard ratio, 7.51 [95% CI, 6.28-8.98]). This risk score can be used to guide decisions regarding venous thromboembolism prophylaxis, although external validation is needed.

Pulmonary Embolism in Pregnancy

Even though venous thromboembolism is a leading cause of maternal mortality in high-income countries, there are limited high-quality data to assist clinicians with the management of pulmonary embolism in this patient population. Diagnosis, prevention, and treatment of pregnancy-associated pulmonary embolism are complicated by the need to consider fetal, as well as maternal, well-being. Recent studies suggest that clinical prediction rules and D-dimer testing can reduce the need for diagnostic imaging in a subset of patients. Low-molecular-weight heparin is the preferred anticoagulant for both prophylaxis and treatment in this setting. Direct oral anticoagulants are contraindicated during pregnancy and in breastfeeding women. Thrombolysis or embolectomy should be considered for pregnant women with pulmonary embolism complicated by hemodynamic instability. Treatment of pregnancy-associated pulmonary embolism should be continued for at least 3 months, including 6 weeks postpartum. Management of anticoagulants at the time of delivery should involve a multidisciplinary individualized approach that uses shared decision making to take patient and caregiver values and preferences into account.

Incidence of VTE in asymptomatic children with deficiencies of antithrombin, protein C, and protein S: a prospective cohort study

Although antithrombin, protein C, and protein S defects are well-recognized inherited risk factors for venous thromboembolism (VTE) in adults, whether they predispose children to these vascular disorders as well is undefined. In a prospective cohort study, we assessed the incidence of spontaneous and risk period-related VTE in children who were family members of adults who, after an episode of symptomatic VTE, had then been identified as carriers of these abnormalities. A total of 134 children from 87 families were enrolled. Seventy (51.5%) of these children were carriers of an inherited defect, and the remaining 64 were not; the mean observation period was 4 years (range, 1-16 years) and 3.9 years (range, 1-13), respectively. Sixteen risk periods were experienced by carriers, and 9 by noncarriers. Six VTE occurred in the 70 carriers during 287 observation-years, accounting for an annual incidence of 2.09% patient-years (95% confidence interval, 0.8-4.5), compared with none in the 64 noncarriers during 248 observation-years. Of the 14 children with thrombophilia who experienced a risk period for thrombosis, 4 (28.6%) developed a VTE episode. The overall incidence of risk-related VTE was 25% per risk period (95% confidence interval, 6.8-64). In conclusion, the thrombotic risk in otherwise healthy children with severe inherited thrombophilia does not seem to differ from that reported for adults with the same defects. Screening for thrombophilia in children who belong to families with these defects seems justified to identify those who may benefit from thromboprophylaxis during risk periods for thrombosis.

American Society of Hematology 2018 guidelines for management of venous thromboembolism: venous thromboembolism in the context of pregnancy

BACKGROUND

Venous thromboembolism (VTE) complicates ∼1.2 of every 1000 deliveries. Despite these low absolute risks, pregnancy-associated VTE is a leading cause of maternal morbidity and mortality.

OBJECTIVE

These evidence-based guidelines of the American Society of Hematology (ASH) are intended to support patients, clinicians and others in decisions about the prevention and management of pregnancy-associated VTE.

METHODS

ASH formed a multidisciplinary guideline panel balanced to minimize potential bias from conflicts of interest. The McMaster University GRADE Centre supported the guideline development process, including updating or performing systematic evidence reviews. The panel prioritized clinical questions and outcomes according to their importance for clinicians and patients. The Grading of Recommendations Assessment, Development and Evaluation (GRADE) approach was used to assess evidence and make recommendations.

RESULTS

The panel agreed on 31 recommendations related to the treatment of VTE and superficial vein thrombosis, diagnosis of VTE, and thrombosis prophylaxis.

CONCLUSIONS

There was a strong recommendation for low-molecular-weight heparin (LWMH) over unfractionated heparin for acute VTE. Most recommendations were conditional, including those for either twice-per-day or once-per-day LMWH dosing for the treatment of acute VTE and initial outpatient therapy over hospital admission with low-risk acute VTE, as well as against routine anti-factor Xa (FXa) monitoring to guide dosing with LMWH for VTE treatment. There was a strong recommendation (low certainty in evidence) for antepartum anticoagulant prophylaxis with a history of unprovoked or hormonally associated VTE and a conditional recommendation against antepartum anticoagulant prophylaxis with prior VTE associated with a resolved nonhormonal provoking risk factor.

Preventing venous thromboembolism during pregnancy and postpartum: crossing the threshold

When should a patient with a known thrombophilia or prior venous thromboembolism (VTE) receive low-molecular-weight heparin (LMWH) prophylaxis during pregnancy and/or the postpartum period? Accurately predicting thrombotic and bleeding risks and knowing what to do with this information is at the heart of decision-making in these challenging scenarios. This article will explore the concept of a risk threshold from clinician and patient perspectives and provide guidance for the use of antepartum and postpartum LMWH prophylaxis in women with a known thrombophilia or prior VTE. Advice for the management of LMWH prophylaxis use around labor and delivery is also reviewed.

In families with inherited thrombophilia the risk of venous thromboembolism is dependent on the clinical phenotype of the proband

The utility of laboratory investigation of relatives of individuals with inherited thrombophilia is uncertain. To assess the risk of venous thromboembolism (VTE) among the carriers, we investigated a family cohort of 1,720 relatives of probands with thrombophilia who were evaluated because of VTE (n=1,088), premature arterial thrombosis (n=113), obstetric complication (n=257), or universal screening before pregnancy or hormonal contraception or therapy (n=262); 968 relatives were carriers of thrombophilia. A first deep venous thrombosis (DVT) occurred in 44 carriers and 10 non-carriers during 37,688 and 29,548 observationyears from birth, respectively. The risk of DVT among the carriers compared with non-carriers was estimated as a hazard ratio (HR). If the proband had VTE and factor V Leiden (FVL) and/or prothrombin (PT)20210A, the HR for DVT was 2.77 (95%CI 1.21–4.82) in the carriers overall, and 5.54 (95%CI 3.20–187.00) in those homozygous or double heterozygous for FVL and PT20210A. If the proband had VTE and a deficiency of antithrombin (AT), protein C or S, the HR for DVT was 5.14 (95%CI 0.88–10.03) in the carriers overall, and 12.86 (95%CI 2.46–59.90) in those with AT deficiency. No increase in risk was found among the carriers who were relatives of the probands who were evaluated for reasons other than VTE. In conclusion, familial investigation for inherited thrombophilia seems justified for probands with previous VTE, but appears of doubtful utility for the relatives of probands without VTE. This should be taken with caution regarding families with deficiency of natural anticoagulants, given the low number of cases analysed.

Circulating microparticles in carriers of factor V Leiden with and without a history of venous thrombosis

Although factor V Leiden (FVL) is a major determinant of thrombotic risk, the reason why less than 10% of carriers eventually develop venous thromboembolic (VTE) events is unknown. Recent observations suggest that circulating levels of microparticles (MP) may contribute to the thrombogenic profile of FVL carriers. We measured the plasma level of annexin V-MP (AMP) platelet-MP (PMP), endothelial-MP (EMP), leukocyte-MP (LMP) and tissue factor-bearing MP (TF+MP), and the MP procoagulant activity (PPL) in 142 carriers of FVL (of these 30 homozygous and 49 with prior VTE), and in 142 age and gender-matched healthy individuals. The mean (± SD) level of AMP was 2,802 ± 853 MP/ μl in carriers and 1,682 ± 897 in controls (p<0.0001). A statistically significant difference between homozygous and heterozygous carriers of FVL was seen in the level of PMP, EMP and LMP, but not in that of the remaining parameters. When the analysis was confined to carriers with and without a VTE history, the mean level of AMP was 3,110 ± 791 MP/ μl in the former, and 2,615 ± 839 MP/μl in the latter (p<0.005). The mean level of all subtypes of circulating MP showed a similar pattern. The PPL clotting time was 39 ± 9 seconds (sec) in carriers, and 52 ± 15 sec in controls (p=0.003); and was 35 ± 8 sec in carriers with prior thrombosis, and 41 ± 10 sec in thrombosis-free carriers (p<0.005). Our study results suggest that circulating MP may contribute to the development of thrombosis in carriers of FVL mutation.

Laboratory assessment of Activated Protein C Resistance/Factor V-Leiden and performance characteristics of a new quantitative assay

Activated Protein C Resistance is mainly associated to a factor V mutation (RQ506), which induces a deficient inactivation of activated factor V by activated protein C, and is associated to an increased risk of venous and arterial thrombosis in affected individuals, caused by the prolonged activated factor V survival. Its prevalence is mainly in Caucasians (about 5%), and this mutation is absent in Africans and Asians. Presence of Factor V-Leiden is usually evidenced with clotting methods, using a two-step APTT assay performed without or with APC: prolongation of blood coagulation time is decreased if this factor is present. The R506Q Factor V-Leiden mutation is now usually characterized using molecular biology, and this technique tends to become the first intention assay for characterization of patients. Both techniques are qualitative, and allow classifying tested individuals as heterozygotes or homozygotes for the mutation, when present. A new quantitative assay for Factor V-Leiden, using a one-step clotting method, has been developed, and designed with highly purified human coagulation proteins. Clotting is triggered with human Factor Xa, in presence of calcium and phospholipids (mixture which favours APC action over clotting process). Diluted tested plasma, is supplemented with a clotting mixture containing human fibrinogen, prothrombin, and protein S at a constant concentration. APC is added, and clotting is initiated with calcium. Calibration is performed with a pool of plasmas from patients carrying the R506Q Factor V mutation, and its mixtures with normal plasma. Homozygous patients have clotting times of about <40sec; heterozygous patients have clotting times of about 40-60sec and normal individuals yield clotting times >70sec. Factor V-Leiden concentration is usually >75% in homozygous patients, 30-60% in heterozygous patients and below 5% in normal. The assay is insensitive to clotting factor deficiencies (II, VII, VIII: C, IX, X), dicoumarol or heparin therapies, and has no interference with lupus anticoagulant (LA). This new assay for Factor V-Leiden can be easily used in any coagulation laboratory, is performed as a single test, and is quantitative. This assay has a high robustness, is accurate and presents a good intra- (<3%) and inter-assay (<5%) variability. It contributes solving most of the laboratory issues faced when testing factor V-Leiden. Quantitation of Factor V-L could contribute to a better assessment of thrombotic risk in affected patients, as this complication is first associated to and caused by the presence of a defined amount of FVa.

Pregnancy, thrombophilia, and the risk of a first venous thrombosis: systematic review and bayesian meta-analysis

Objective To provide evidence to support updated guidelines for the management of pregnant women with hereditary thrombophilia in order to reduce the risk of a first venous thromboembolism (VTE) in pregnancy.Design Systematic review and bayesian meta-analysis.Data sources Embase, Medline, Web of Science, Cochrane Library, and Google Scholar from inception through 14 November 2016.Review methods Observational studies that reported on pregnancies without the use of anticoagulants and the outcome of first VTE for women with thrombophilia were eligible for inclusion. VTE was considered established if it was confirmed by objective means, or when the patient had received a full course of a full dose anticoagulant treatment without objective testing. Results 36 studies were included in the meta-analysis. All thrombophilias increased the risk for pregnancy associated VTE (probabilities ≥91%). Regarding absolute risks of pregnancy associated VTE, high risk thrombophilias were antithrombin deficiency (antepartum: 7.3%, 95% credible interval 1.8% to 15.6%; post partum: 11.1%, 3.7% to 21.0%), protein C deficiency (antepartum: 3.2%, 0.6% to 8.2%; post partum: 5.4%, 0.9% to 13.8%), protein S deficiency (antepartum: 0.9%, 0.0% to 3.7%; post partum: 4.2%; 0.7% to 9.4%), and homozygous factor V Leiden (antepartum: 2.8%, 0.0% to 8.6%; post partum: 2.8%, 0.0% to 8.8%). Absolute combined antepartum and postpartum risks for women with heterozygous factor V Leiden, heterozygous prothrombin G20210A mutations, or compound heterozygous factor V Leiden and prothrombin G20210A mutations were all below 3%. Conclusions Women with antithrombin, protein C, or protein S deficiency or with homozygous factor V Leiden should be considered for antepartum or postpartum thrombosis prophylaxis, or both. Women with heterozygous factor V Leiden, heterozygous prothrombin G20210A mutation, or compound heterozygous factor V Leiden and prothrombin G20210A mutation should generally not be prescribed thrombosis prophylaxis on the basis of thrombophilia and family history alone. These data should be considered in future guidelines on pregnancy associated VTE risk.

Outcome of Patients with Venous Thromboembolism and Factor V Leiden or Prothrombin 20210 Carrier Mutations During the Course of Anticoagulation

BACKGROUND

Individuals with factor V Leiden or prothrombin G20210A mutations are at a higher risk to develop venous thromboembolism. However, the influence of these polymorphisms on patient outcome during anticoagulant therapy has not been consistently explored.

METHODS

We used the Registro Informatizado de Enfermedad TromboEmbólica database to compare rates of venous thromboembolism recurrence and bleeding events occurring during the anticoagulation course in factor V Leiden carriers, prothrombin mutation carriers, and noncarriers.

RESULTS

Between March 2001 and December 2015, 10,139 patients underwent thrombophilia testing. Of these, 1384 were factor V Leiden carriers, 1115 were prothrombin mutation carriers, and 7640 were noncarriers. During the anticoagulation course, 160 patients developed recurrent deep vein thrombosis and 94 patients developed pulmonary embolism (16 died); 154 patients had major bleeding (10 died), and 291 patients had nonmajor bleeding. On multivariable analysis, factor V Leiden carriers had a similar rate of venous thromboembolism recurrence (adjusted hazard ratio [HR], 1.16; 95% confidence interval [CI], 0.82-1.64), half the rate of major bleeding (adjusted HR, 0.50; 95% CI, 0.25-0.99) and a nonsignificantly lower rate of nonmajor bleeding (adjusted HR, 0.66; 95% CI, 0.43-1.01) than noncarriers. Prothrombin mutation carriers and noncarriers had a comparable rate of venous thromboembolism recurrence (adjusted HR, 1.00; 95% CI, 0.68-1.48), major bleeding (adjusted HR, 0.75; 95% CI, 0.42-1.34), and nonmajor bleeding events (adjusted HR, 1.10; 95% CI, 0.77-1.57).

CONCLUSIONS

During the anticoagulation course, factor V Leiden carriers had a similar risk for venous thromboembolism recurrence and half the risk for major bleeding compared with noncarriers. This finding may contribute to decision-making regarding anticoagulation duration in selected factor V Leiden carriers with venous thromboembolism.

Association Between Thrombophilic Gene Mutations and the Risk of Vascular Access Thrombosis in Hemodialysis Patients

The cause of thrombosis in hemodialysis vascular access is considered to be of a multifactorial nature, including stenosis of the venous or arterial connection. Therefore, identification of relevant thrombotic risk factors could lead to an improved antithrombotic therapy. This case control study was performed to evaluate the relationship between Factor V (G1691A and A4070G) and Factor II polymorphisms and vascular access thrombosis in hemodialysis patients. One hundred and twenty-one patients undergoing dialysis were selected as subjects. This sample was divided into two groups; a case group of 60 patients who had sustained one or more thrombotic events that resulted in vascular access failure and a control group of 61 patients, who never had a thrombotic occlusion of a functioning permanent dialysis access. Our data demonstrated a significantly increased risk of vascular access thrombosis in carriers of the mutant FV (G1691A and A4070G) polymorphisms (P < 0.05).Further studies on a large-scale population and other genetic variants will be needed to find candidate genes for vascular access thrombosis in hemodialysis patients.

Guidance for the treatment and prevention of obstetric-associated venous thromboembolism

Venous thromboembolism (VTE), which may manifest as pulmonary embolism (PE) or deep vein thrombosis (DVT), is a serious and potentially fatal condition. Treatment and prevention of obstetric-related VTE is complicated by the need to consider fetal, as well as maternal, wellbeing when making management decisions. Although absolute VTE rates in this population are low, obstetric-associated VTE is an important cause of maternal morbidity and mortality. This manuscript, initiated by the Anticoagulation Forum, provides practical clinical guidance on the prevention and treatment of obstetric-associated VTE based on existing guidelines and consensus expert opinion based on available literature where guidelines are lacking.

A semiquantitative metric for evaluating clinical actionability of incidental or secondary findings from genome-scale sequencing

PURPOSE

As genome-scale sequencing is increasingly applied in clinical scenarios, a wide variety of genomic findings will be discovered as secondary or incidental findings, and there is debate about how they should be handled. The clinical actionability of such findings varies, necessitating standardized frameworks for a priori decision making about their analysis.

METHODS

We established a semiquantitative metric to assess five elements of actionability: severity and likelihood of the disease outcome, efficacy and burden of intervention, and knowledge base, with a total score from 0 to 15.

RESULTS

The semiquantitative metric was applied to a list of putative actionable conditions, the list of genes recommended by the American College of Medical Genetics and Genomics (ACMG) for return when deleterious variants are discovered as secondary/incidental findings, and a random sample of 1,000 genes. Scores from the list of putative actionable conditions (median = 12) and the ACMG list (median = 11) were both statistically different than the randomly selected genes (median = 7) (P < 0.0001, two-tailed Mann-Whitney test).

CONCLUSION

Gene-disease pairs having a score of 11 or higher represent the top quintile of actionability. The semiquantitative metric effectively assesses clinical actionability, promotes transparency, and may facilitate assessments of clinical actionability by various groups and in diverse contexts.Genet Med 18 5, 467-475.

Budd-Chiari Syndrome in a Patient with JAK-2 V617F and Factor V G1691A Mutations

Myeloproliferative neoplasms (MPN) are considered a risk factor for Budd-Chiari syndrome (BCS). The current classification of MPN by the World Health Organization is based on the presence of JAK-2 V617F somatic mutation, which is present in 40 to 60% of patients with BCS. Factor V Leiden mutation is found in around 53% of patients with BCS, representing the most common prothrombotic disease associated with the disorder. We describe a 48-year old woman with a past medical history of deep venous thrombosis in the left upper extremity and one episode in both lower extremities, one episode of transient ischaemic attack and essential thrombocythemia, who presented with jaundice, ascites and hepatomegaly. Budd-Chiari syndrome was diagnosed based on findings on Doppler ultrasound and liver biopsy. Doppler ultrasound showed narrowness of hepatic veins and inferior vena cava in its hepatic portion, diffuse echotexture and portal hypertension. Liver biopsy showed congestion of sinusoids and portal fibrosis. The patient was found to be a heterozygous carrier of Factor V and homozygous wild type G20210A prothrombin mutations. The JAK-2 V617F mutation was detected by allele-specific polymerase chain reaction (AS-PCR). The association of these mutations is rare, with only a few cases reported in the literature. The patient was treated with oral anticoagulation and antiplatelets with good results and proper follow-up. In conclusion, due to the possible coexistence of multiple prothrombotic factors in patients with Budd-Chiari syndrome, the approach to these patients must be focussed on searching for multiple factors and should include the JAK-2 V617F mutation.

Are MPNs vascular diseases?

A high risk of arterial and venous thrombosis is the hallmark of chronic myeloproliferative neoplasms (MPNs), particularly polycythemia vera (PV) and essential thrombocythemia (ET). Clinical aspects, pathogenesis and management of thrombosis in MPN resemble those of other paradigmatic vascular diseases. The occurrence of venous thrombosis in atypical sites, such as the splanchnic district, and the involvement of plasmatic prothrombotic factors, including an acquired resistance to activated protein C, both link MPN to inherited thrombophilia. Anticoagulants are the drugs of choice for these complications. The pathogenic role of leukocytes and inflammation, and the high mortality rate from arterial occlusions are common features of MPN and atherosclerosis. The efficacy and safety of aspirin in reducing deaths and major thrombosis in PV have been demonstrated in a randomized clinical trial. Finally, the Virchow's triad of impaired blood cells, endothelium and blood flow is shared both by MPN and thrombosis in solid cancer. Phlebotomy and myelosuppressive agents are the current therapeutic options for correcting these abnormalities and reducing thrombosis in this special vascular disease represented by MPN.

Preventing thrombophilia-related complications of pregnancy: an update

Approximately half of all pregnancy-related venous thromboembolic events are associated with thrombophilia. Although the most compelling data for a link between thrombophilia and other adverse pregnancy outcomes derive from women with antiphospholipid antibodies, some studies also suggest an association between these pregnancy complications and hereditary thrombophilias. Management of thrombophilia often involves anticoagulant therapy; however, use of these agents during pregnancy is challenging. There is a paucity of high-quality studies and consequently, recommendations are based largely on extrapolation from data in nonpregnant women, in addition to observational studies and a few small randomized studies. This article will review the impact of the thrombophilias on pregnancy and its outcome, evidence for therapies aimed at the prevention of thrombophilia-related pregnancy complications, and the most recent recommendations contained in the 9th Edition of the American College of Chest Physicians Evidence-Based Clinical Practice Guidelines.

Pregnancy-associated venous thromboembolism: prevention and treatment

Pregnancy is associated with an increased risk of venous thromboembolism (VTE) and this condition remains an important cause of maternal morbidity and mortality. The use of anticoagulant therapy for treatment and prophylaxis of VTE during pregnancy is challenging because of the potential for fetal, as well as maternal, complications. Although evidence-based recommendations for the use of anticoagulants have been published, given the paucity of available data, guidelines are based largely upon observational studies and from data in nonpregnant patients. This article reviews the available literature and provides guidance for the management and prevention of VTE during pregnancy.

VTE, thrombophilia, antithrombotic therapy, and pregnancy: Antithrombotic Therapy and Prevention of Thrombosis, 9th ed: American College of Chest Physicians Evidence-Based Clinical Practice Guidelines

BACKGROUND

The use of anticoagulant therapy during pregnancy is challenging because of the potential for both fetal and maternal complications. This guideline focuses on the management of VTE and thrombophilia as well as the use of antithrombotic agents during pregnancy.

METHODS

The methods of this guideline follow the Methodology for the Development of Antithrombotic Therapy and Prevention of Thrombosis Guidelines: Antithrombotic Therapy and Prevention of Thrombosis, 9th ed: American College of Chest Physicians Evidence-Based Clinical Practice Guidelines in this supplement.

RESULTS

We recommend low-molecular-weight heparin for the prevention and treatment of VTE in pregnant women instead of unfractionated heparin (Grade 1B). For pregnant women with acute VTE, we suggest that anticoagulants be continued for at least 6 weeks postpartum (for a minimum duration of therapy of 3 months) compared with shorter durations of treatment (Grade 2C). For women who fulfill the laboratory criteria for antiphospholipid antibody (APLA) syndrome and meet the clinical APLA criteria based on a history of three or more pregnancy losses, we recommend antepartum administration of prophylactic or intermediate-dose unfractionated heparin or prophylactic low-molecular-weight heparin combined with low-dose aspirin (75-100 mg/d) over no treatment (Grade 1B). For women with inherited thrombophilia and a history of pregnancy complications, we suggest not to use antithrombotic prophylaxis (Grade 2C). For women with two or more miscarriages but without APLA or thrombophilia, we recommend against antithrombotic prophylaxis (Grade 1B).

CONCLUSIONS

Most recommendations in this guideline are based on observational studies and extrapolation from other populations. There is an urgent need for appropriately designed studies in this population.

Factor V Leiden thrombophilia

Factor V Leiden is a genetic disorder characterized by a poor anticoagulant response to activated Protein C and an increased risk for venous thromboembolism. Deep venous thrombosis and pulmonary embolism are the most common manifestations, but thrombosis in unusual locations also occurs. The current evidence suggests that the mutation has at most a modest effect on recurrence risk after initial treatment of a first venous thromboembolism. Factor V Leiden is also associated with a 2- to 3-fold increased relative risk for pregnancy loss and possibly other obstetric complications, although the probability of a successful pregnancy outcome is high. The clinical expression of Factor V Leiden is influenced by the number of Factor V Leiden alleles, coexisting genetic and acquired thrombophilic disorders, and circumstantial risk factors. Diagnosis requires the activated Protein C resistance assay (a coagulation screening test) or DNA analysis of the F5 gene, which encodes the Factor V protein. The first acute thrombosis is treated according to standard guidelines. Decisions regarding the optimal duration of anticoagulation are based on an individualized assessment of the risks for venous thromboembolism recurrence and anticoagulant-related bleeding. In the absence of a history of thrombosis, long-term anticoagulation is not routinely recommended for asymptomatic Factor V Leiden heterozygotes, although prophylactic anticoagulation may be considered in high-risk clinical settings. In the absence of evidence that early diagnosis reduces morbidity or mortality, decisions regarding testing at-risk family members should be made on an individual basis.

High prevalence of thrombophilic traits in children with family history of thromboembolism

OBJECTIVES

To determine a proximate family history of venous thromboembolism (VTE) in (1) the prevalence of thrombophilia; (2) the frequency of recommended changes in management resulting from thrombophilia evaluation; and (3) outcomes in longitudinal follow-up.

STUDY DESIGN

Laboratory thrombophilia investigation was performed in 56 children with first- or second-degree family history of thromboembolism before age 55 years, but without personal history of thromboembolism, who were enrolled in a prospective inception cohort. VTE risk factors, family history, thrombophilia findings, and management recommendations were systematically collected, along with thromboembolism risk episodes/exposures, prophylactic anticoagulation, major bleeds, and thromboembolism events during follow-up.

RESULTS

The frequencies of all thrombophilia traits were higher than the general population. Among 32 children who underwent complete laboratory evaluation, 34% had >or=2 traits. Thrombophilia testing led to recommendations for risk-based transient antithrombotic prophylaxis in 71% of subjects. No thromboembolism episodes developed during more than 900 patient-months of follow-up, although at-risk exposures were infrequent.

CONCLUSION

Risk-stratified approaches to primary prevention of pediatric VTE should be further evaluated in cooperative prospective studies.

[Questionnaire for assessing the risk of venous thromboembolism in hospitalized surgical and non-surgical patients in the 4th Hungarian antithrombotic guideline entitled "Risk reduction and treatment of venous thromboembolism"]

A large proportion of hospitalized surgical and medical patients are at risk for venous thromboembolism. Depending on the type of surgical intervention, venous thrombosis develops in 15-60% of surgical patients without prophylaxis. Although venous thromboembolism is most often considered to be associated with recent surgery or trauma, 50 to 70% of symptomatic thromboembolic events and 70 to 80% of fatal pulmonary embolisms occur in nonsurgical patients. International and national registries show that the majority of at-risk surgical patients actually received the appropriate thromboembolic prophylaxis. However, despite of international and national recommendations, prophylaxis was not provided for a large proportion of at-risk medical patients. The rate of medical patients receiving prophylaxis should be increased, and appropriate thrombosis prophylaxis should be offered to at-risk medical patients. The thrombosis risk assessment is an important tool to identify patients at increased risk for venous thromboembolism, to simplify decision making on prophylaxis administration, and to improve the adherence to guidelines. When the risk is recognized, if there is no contraindication, prophylaxis should be ordered. The 4th Hungarian Antithrombotic Guideline entitled "Risk reduction and treatment of thromboembolism" calls attention to the importance of risk assessment and for the first time it includes and recommends risk assessment models for hospitalized surgical and medical patients. The risk assessment models are presented and the evidence based data for the different risk factors included in these models are reviewed.

Deciphering the molecular basis of venous thromboembolism: where are we and where should we go?

Venous thromboembolism (VTE) is a frequent disease that has a major genetic component of risk. However, known identified genetic risk factors account for <30% of idiopathic (without any environmental origin) VTE cases. This article aims to review the lessons learnt during recent decades in the field of the genetics of VTE, describe the present state-of-art methods and discuss promising themes for finding new susceptibility loci.

X-linked thrombophilia with a mutant factor IX (factor IX Padua)

We report a case of juvenile thrombophilia associated with a substitution of leucine for arginine at position 338 (R338L) in the factor IX gene (factor IX-R338L). The level of the mutant factor IX protein in plasma was normal, but the clotting activity of factor IX from the proband was approximately eight times the normal level. In vitro, recombinant factor IX-R338L had a specific activity that was 5 to 10 times as high as that in the recombinant wild-type factor IX. The R338 substitution causes a gain-of-function mutation, resulting in factor IX that is hyperfunctional.

Fator V de Leiden na doença de Legg-Calvé-Perthes

Trobofilias hereditárias têm sido implicadas na patogênese da doenca de Legg-Calvé-Perthes. Uma investigação do fator de risco hereditário mais comum para hipercoagulabilidade - a mutação no gene do fator V (fator V de Leiden) - foi conduzida em 20 pacientes com Legg-Calvé-Perthes e 214 controles sadios. A prevalência do fator V de Leiden foi maior nos pacientes com Legg-Calvé-Perthes que no grupo controle (30 vs. 1,87%). A razão de chances (odds ratio) para o desenvolvimento de Legg-Calvé-Perthes foi de 22,5 (p<0,05; intervalo de confiança: 5,68- 89.07). Estes dados sugerem, o fator V de Leiden como fator de risco hereditário para hipercoagulabilidade associada ao desenvolvimento da doença de Legg-Calvé-Perthes.

Manifestações cutâneas das trombofilias

O escopo deste artigo é revisar os estados de hipercoagulabilidade sangüínea (trombofilias) mais provavelmente encontrados por dermatologista. Seus sinais cutâneos incluem o livedo reticular, necrose cutânea, ulcerações e isquemia digital, púrpura retiforme, além de úlceras nas pernas. Revisamos seu tratamento adequado, bem como ressaltamos as manifestações cutâneas que impõem pesquisa laboratorial de trombofilias e os exames indicados nessas situações.

Oral contraception and thrombophilia

PURPOSE OF REVIEW

To describe current knowledge related to the association between oral contraception and the thrombophilias.

RECENT FINDINGS

The use of oral contraception increases the risk of venous thromboembolism as well as arterial thrombosis. Third-generation pills seem to increase the risk of venous thromboembolism compared with second-generation pills. This effect seems to be reversed or absent for the risk of arterial thrombosis. The effect of oral contraception on the risk of venous thromboembolism is more pronounced during the first year of use. All these risks are further increased in patients with an inborn or acquired tendency for coagulation (thrombophilia).

SUMMARY

Prospective users of oral contraception are potential candidates for screening/testing, because a positive screen may substantially decrease the risk of a thrombotic event. At present, the available testing methods are not cost effective, and the absolute risk is not defined for each thrombophilia. Until these shortcomings are solved, it is not recommended to test every woman who wishes to use oral contraception. Nevertheless, before starting on oral contraception, each patient should be carefully screened by a physician who should identify an increased risk of thrombophilia and tailor the laboratory testing.

Increased Factor V Leiden frequency is associated with venous thrombotic events among young Brazilian patients

INTRODUCTION

Of the inherited thrombophilias, the Factor V Leiden (FVL) and the prothrombin mutant (FII G20210A) are associated with increased risk of venous thromboembolism (VTE). The C677T mutation of the methylenetetrahydrofolate reductase gene, which may lead to hyperhomocysteinemia, is also considered a risk factor for VTE in some studies. However, the frequency of these genetic risk factors may vary significantly among different populations.

MATERIAL AND METHODS

The FVL, FII G20210A and C677T mutations were investigated by PCR-RFLP in 275 young VTE Brazilian patients as well as in 324 biologically unrelated individuals selected to compose the control group.

RESULTS

The C677T mutation in the MTHFR gene was detected in 135 (49.1%) patients, of which 117 (42.5%) were identified as heterozygous and 18 (6.5%) as homozygous. The G20210A mutation was detected in 14 (5.1%) patients in heterozygosis. In both cases, no significant difference was observed when these results were compared to the frequencies observed in the control group. FVL was detected in heterozygosis in 19 (6.9%) patients, corresponding to a significantly increased frequency when compared to that observed for the control group (1.2%) (OR 5.9; 95% CI 2.08-16.79; p < 0.001).

CONCLUSIONS

The data indicated that FVL is significantly associated with VTE among young Brazilian patients, but also supported previous evidence that VTE is a multi-factorial disease, resulting from the interaction of genetic and acquired risk factors.

Who should be tested for thrombophilia?

PURPOSE OF REVIEW

The purpose of this review is to identify on the basis of available data and expert opinions who would benefit most from screening for thrombophilia.

RECENT FINDINGS

Recent studies have clearly defined the risk of venous thromboembolism in members of families with inherited thrombophilia. Meta-analyses have shown the role of the most common thrombophilic conditions in increasing the risk of recurrent venous thromboembolism in carriers. Screening for thrombophilia in venous thromboembolism patients might help identify those at higher risk of recurrences even though it is unclear how this information can be of use in modifying their management. Thrombophilia seems to play a role in early fetal losses as also shown in women at their first intended pregnancy, which makes it interesting to screen women after only one bad pregnancy outcome.

SUMMARY

Screening for thrombophilia can be performed particularly in young patients with venous thromboembolism. Carriers of inherited thrombophilia are at increased risk of venous thromboembolism recurrences. Screening families of venous thromboembolism patients with thrombophilia allows the identification of still asymptomatic carriers who may benefit from thromboprophylaxis. This may be true of women in fertile age belonging to thrombophilic families. In thrombophilic women with pregnancy complications prophylaxis may be offered to prevent recurrences.

The scientific basis for evaluation and management of thrombotic disorders

The hemostatic mechanisms at work in the body involve a complex series of interactions between platelets, the endothelium, and the coagulation cascade. Much has been learned regarding the molecular mechanisms governing these intricate processes. The hypercoagulable state involves a disruption of the normal homeostatic equilibrium. This state may be either inherent or acquired. The prevention of associated thromboembolic complications requires therapeutic anticoagulation. A broader understanding of the factors contributing to these prothrombotic tendencies and the subtleties involved in their management provides the surgeon with another weapon in the armamentarium to promote better and safer patient outcomes.

Screening for Thrombophilia

Thrombophilia screening may be useful in patients at high risk of VTE because it may improve clinical outcome. Family screening allows primary prophylaxis for high-risk situations and counseling of women considering hormonal therapy and pregnancy. Until we find useful and inexpensive screening tools, it is not recommended to test every patient or her/his relatives. Each index case should be carefully evaluated by an expert physician who should tailor the laboratory testing and treatment modalities.

Can haematological tests predict cardiovascular risk? The 2005 Kettle Lecture*

The risk of venous or arterial thrombosis is routinely assessed by clinical variables (risk factors) supplemented by measurement of blood lipids and glucose for arterial thrombotic events. Haematological tests that might play a role in risk prediction include haemostatic variables, haematocrit and inflammatory markers (erythrocyte sedimentation rate, plasma viscosity, white cell count). Recent epidemiological studies of these phenotypes and related genotypes are reviewed. For the risk prediction of first venous thrombosis, screening for thrombophilias in 'high-risk' situations does not appear clinically effective or cost-effective; with the possible exception of women considering oral hormone replacement therapy. General screening after a first venous event to predict recurrence (or risk in asymptomatic relatives) does not appear effective; with the possible exception of d-dimer, which requires further study. For risk prediction of first arterial thrombosis, screening adds little to prediction by current clinical risk scores. Screening of persons after a first arterial event, or with atrial fibrillation (e.g. with D-dimer for stroke prediction), requires further study. In conclusion, haematological tests have very limited roles in the prediction of cardiovascular risk, and should only be used according to evidence-based guidelines. The need for management studies is highlighted.

Issues concerning the laboratory investigation of inherited thrombophilia

Inherited thrombophilia, defined as an increased familial tendency to develop thrombosis, may be due to congenital deficiencies or abnormalities of antithrombin, protein C or protein S; to the presence of a point mutation in the factor V gene (G1691A, factor V Leiden) leading to a poor anticoagulant response to activated protein C; or to the presence of a mutation in the prothrombin gene (G20210A) leading to increased plasma levels of prothrombin. The laboratory investigation of inherited thrombophilia should be limited to patients with a history of venous thromboembolism and, if positive, to their family members even though they are still asymptomatic. There is no indication for indiscriminate screening of the general population or screening of asymptomatic women before prescribing oral contraceptives. Testing should be based on the phenotype for antithrombin, protein C and protein S; on the phenotype and genotype (factor V Leiden mutation) for activated protein C resistance; and on the genotype (G20210A mutation) for hyperprothrombinemia. Phenotypic testing should be performed no sooner than three months after acute thrombotic events and at least 2 weeks after discontinuation of oral anticoagulant treatment.

Hypercoagulability markers in young asymptomatic heterozygous carriers of factor V Leiden (G1691A) or prothrombin (G20210A) variant

BACKGROUND

Mutations in factor V (factor V Leiden-G1691A) and prothrombin (G20210A) genes are important risk factors for thrombophilia due to their high incidence in patients with thromboembolic events, especially among the young. However, it is not clear if levels of hypercoagulability markers are significantly altered in asymptomatic young carriers of factor V Leiden or prothrombin G20210A.

METHODS

Hemostatic status of 32 asymptomatic young individuals carrying these mutations and of 18 normal control individuals was investigated through the determination of plasma thrombomodulin (TM), prothrombin fragment 1+2 (F1+2), thrombin-antithrombin complex (TAT) and D-dimer.

RESULTS

No significant differences were observed in these hemostatic markers when comparing groups of individuals carrying mutations and the control group.

CONCLUSION

Analysis of these results leads to the conclusion that the presence of these mutations, in the absence of acquired risk factors, does not constantly predispose these young carriers to a state of hypercoagulability.

The measurement and application of thrombin generation

It is the capacity to generate thrombin, and the enzymatic work that thrombin does, that determines blood coagulability. Therefore, measurement of the enzymatic work potential of thrombin provides a method for quantifying the composite effect of the multiple factors that determine coagulation capacity. The application of measurement of thrombin generation to clinical decision making has been hampered by numerous technical difficulties and pitfalls, many of which have now been overcome. Technical advances now permit rapid, reproducible measurement. A review of clinical studies performed to date indicates the need to appreciate the precise methodology used in each case and the need to consider standardisation in future studies. Applying thrombin generation measurement to clinical decision making will require up-to-date estimates of risks relating to the disorder and the intended therapeutic intervention. Ultimately management studies will be required if the clinical utility of measurement of thrombin generation is to be proven.

Comparison of incidence/risk of venous thromboembolism (VTE) among selected clinical and hereditary risk markers: a community-based cohort study

Background

Little information is available from community-based long-term VTE cohort studies to compare the absolute thrombosis risk of established clinical and genetic risk factors.

Materials and methods

The occurrence of venous thromboembolism (VTE) was observed during a 10-year observation period in the BAvarian ThromboEmbolic Risk (BATER) study, a cohort study of 4337 women (age 18–55 years). We collected data on demographics, reproductive life, lifestyle, conditions/diseases, and particularly potential risk factors for VTE with a self-administered questionnaire. The objective was to present incidence rates of VTE and to show relative risk estimated associated with different clinical and genetic risk factors.

Results

34 new, by diagnostic means confirmed VTE events occurred during the observation time of 32,656 women-years (WY). The overall incidence of VTE was 10.4 per 10⁴ WY. The incidence rates varied markedly among different risk cohorts. The highest incidence was observed in women with previous history of VTE, followed by family history of VTE. None of the measured "genetically-related risk markers" (antithrombin, protein C, FVL, prothrombin mutation, or MTHFR) showed a significant VTE risk.

Conclusion

Most of the discussed VTE risk factors showed no significant association with the occurrence of new VTEs due to smallness of numbers. Only first-degree family history of VTE and own history of a previous VTE event depicted a significant association with future VTE. Clinical information seems to be more important to determine future VTE risk than genetically related laboratory tests.

VTE Risk assessment - a prognostic Model: BATER Cohort Study of young women

Background

Community-based cohort studies are not available that evaluated the predictive power of both clinical and genetic risk factors for venous thromboembolism (VTE). There is, however, clinical need to forecast the likelihood of future occurrence of VTE, at least qualitatively, to support decisions about intensity of diagnostic or preventive measures.

Materials and methods

A 10-year observation period of the Bavarian Thromboembolic Risk (BATER) study, a cohort study of 4337 women (18–55 years), was used to develop a predictive model of VTE based on clinical and genetic variables at baseline (1993). The objective was to prepare a probabilistic scheme that discriminates women with virtually no VTE risk from those at higher levels of absolute VTE risk in the foreseeable future. A multivariate analysis determined which variables at baseline were the best predictors of a future VTE event, provided a ranking according to the predictive power, and permitted to design a simple graphic scheme to assess the individual VTE risk using five predictor variables.

Results

Thirty-four new confirmed VTEs occurred during the observation period of over 32,000 women-years (WYs). A model was developed mainly based on clinical information (personal history of previous VTE and family history of VTE, age, BMI) and one composite genetic risk markers (combining Factor V Leiden and Prothrombin G20210A Mutation). Four levels of increasing VTE risk were arbitrarily defined to map the prevalence in the study population: No/low risk of VTE (61.3%), moderate risk (21.1%), high risk (6.0%), very high risk of future VTE (0.9%). In 10.6% of the population the risk assessment was not possible due to lacking VTE cases. The average incidence rates for VTE in these four levels were: 4.1, 12.3, 47.2, and 170.5 per 10⁴ WYs for no, moderate, high, and very high risk, respectively.

Conclusion

Our prognostic tool – containing clinical information (and if available also genetic data) – seems to be worthwhile testing in medical practice in order to confirm or refute the positive findings of this study. Our cohort study will be continued to include more VTE cases and to increase predictive value of the model.

Management of thrombophilia: who to screen?

Testing for laboratory evidence of heritable thrombophilia is now common. This practice undoubtedly arose in response to association studies, which revealed the influence of heritable thrombophilic defects on the development of VTE. Now that high quality clinical outcome studies are being reported it is becoming apparent that despite association, testing has limited predictive value for the majority of unselected symptomatic patients. Clearly, there is a difference between the ability of a test to explain why one individual is more likely to suffer a thrombosis than another and the ability of the same test to predict which patients who have already had thrombosis are likely to suffer a recurrence. In the absence of grade A recommendations, it is inevitable that practice will vary. Decisions will be influenced by local resources, competing demands for clinical and laboratory services and not least the professional interest of the haematologist. If thrombophilia testing is performed there is a strong case for selecting patients for testing as in most cases decisions regarding intensity and duration of anticoagulant therapy can be made purely in relation to clinical criteria.

Risk of a first venous thrombotic event in carriers of a familial thrombophilic defect. The European Prospective Cohort on Thrombophilia (EPCOT)

BACKGROUND

Reliable risk estimates for venous thrombosis in families with inherited thrombophilia are scarce but necessary for determining optimal screening and treatment policies.

OBJECTIVES

In the present analysis, we determined the risk of a first venous thrombotic event in carriers of a thrombophilic defect (i.e. antithrombin-, protein C- or protein S deficiency, or factor V Leiden).

PATIENTS AND METHODS

The asymptomatic carriers had been tested prior to this study in nine European thrombosis centers because of a symptomatic carrier in the family, and were followed prospectively for 5.7 years on average between March 1994 and January 2001. Annually, data were recorded on the occurrence of risk situations for venous thrombosis and events (e.g. venous thrombosis, death).

RESULTS

Twenty-six of the 575 asymptomatic carriers (4.5%) and seven of the 1118 controls (0.6%) experienced a first deep venous thrombosis or pulmonary embolism during follow-up. Of these events, 58% occurred spontaneously in the carriers compared with 43% in the controls. The incidence of first events was 0.8% per year (95% CI 0.5-1.2) in the carriers compared with 0.1% per year (95% CI 0.0-0.2) in the controls. The highest incidence was associated with antithrombin deficiency or combined defects, and the lowest incidence with factor V Leiden.

CONCLUSIONS

The incidence of venous events in asymptomatic individuals from thrombophilic families does not exceed the risk of bleeding associated with long-term anticoagulant treatment in the literature (1-3%).

Liver transplantation as definitive treatment for a factor V Leiden mutation

Liver transplantation (LT) was achieved for factor V Leiden-induced thrombophilia in a neonate with hepatic veno-occlusive disease. Initial LT was performed with a liver segment removed from a child with primary oxalosis. Four months later, a second, definitive LT was performed. The child remains well without recurrent thrombosis.

The incidence of venous thromboembolism among Factor V Leiden carriers: a community-based cohort study

While Factor V (FV) Leiden is a risk factor for venous thromboembolism (VTE), the incidence of VTE among FV Leiden carriers is uncertain. The objective of the study was to estimate the overall age-specific and pregnancy-related VTE incidence and the relative risk among FV Leiden carriers. In a community-based sample of 3424 south-eastern Minnesota residents, 230 (6.7%) were genotyped as FV Leiden carriers; 220 carriers (mean age = 68 years) could be matched to a non-carrier on age, gender, ethnicity and length of medical history. We performed a retrospective cohort study of carriers and non-carriers by reviewing the complete medical records in the community for demographic and baseline characteristics, pregnancies and live births, and first lifetime VTE. Over 14 722 person-years, 24 (10.9%) carriers developed VTE [overall incidence = 163 (95% CI 104, 242) per 100,000 person-years]. VTE incidence rates for ages 15-29, 30-44, 45-59 and > or = 60 years were 0, 61, 244 and 764 per 100,000 person-years, respectively (cumulative VTE incidence at age 65 years = 6.3%). VTE incidence for carriers did not differ significantly from that for non-carriers except for those > or = 60 years old (relative risk = 3.6; 95% CI 2.0, 6.0). There were 311 live births among 130 women carriers; no VTE events occurred during pregnancy or postpartum [incidence = 0 (95% CI 0, 1186) per 100,000 women-years]. Most FV Leiden carriers do not develop VTE. Among all carriers, those > or = 60 years old are at the highest risk for VTE. The incidence of VTE among asymptomatic women carriers during pregnancy is low and insufficient to warrant prophylaxis.

Elevated levels of FVIII:C within families are associated with an increased risk for venous and arterial thrombosis

Elevated levels of coagulation factor VIII:C (FVIII:C) are associated with an increased risk for venous and arterial thromboembolism. Whether relatives of patients with elevated levels of FVIII:C are also at increased risk for thrombotic disease is unknown. The objective was to determine the annual incidences of both venous and arterial thrombotic events in first-degree relatives of patients with elevated levels of FVIII:C and venous thromboembolism (VTE) or premature atherosclerosis. A retrospective study with 584 first-degree relatives of 177 patients with elevated levels of FVIII:C was performed. The level of FVIII:C was determined and relatives with elevated and normal levels of FVIII:C were compared. Of the participants, 40% had elevated levels of FVIII:C. The annual incidence of a first episode of VTE was 0.34% and 0.13% in relatives with elevated levels of FVIII:C and those with normal levels, respectively [OR 3.7 (95% CI 1.9-7.5)]. The absolute annual incidence in the youngest age group with elevated levels of FVIII:C was 0.16% (0.05-0.37) and gradually increased to 0.99% (0.40-2.04) in those older than 60 years of age, although the odds ratios were not statistically significant. The annual incidences of a first arterial thrombotic event were 0.29% and 0.14% in relatives with and without elevated levels of FVIII:C, respectively [OR 3.1 (1.4-6.6)]. In particular the risks for a first myocardial infarction [OR 4.3 (1.0-18.1); P =0.046] and a first peripheral arterial thrombosis [OR 8.6 (1.6-47.6)] were increased. Within families of patients with elevated levels of FVIII:C and VTE or premature atherosclerosis, 40% of their first-degree relatives has elevated levels of FVIII:C as well, and they are at increased risk for both VTE and arterial thrombosis as compared with their relatives with normal levels.