Thromboembolic disease is the leading cause of morbidity and mortality in the developed world (America Heart Association 2010. Circulation 2010;121:e46-e215). Arterial thrombosis is the most common underlying cause of acute myocardial infarction, non-hemorrhagic cerebrovascular accidents, and peripheral vascular disease. Pathological manifestations of venous thromboembolism (VTE) largely include deep vein thrombosis (DVT) and pulmonary embolus (PE). While arterial thromboembolic events are the foremost cause of death and disability, venous disease also plays an important role. VTE occurs for the first time in 100 per 100 000 persons each year in the United States (America Heart Association 2010. Circulation 2010;121:e46-e215). Approximately one third of patients with symptomatic VTE manifest PE, whereas two thirds manifest DVT alone (America Heart Association 2010. Circulation 2010;121:e46-e215). PE is the most common cause of preventable hospital death accounting for 60.000 deaths in the United States annually (Anderson F A. Arch Intem Med 1991:151:933-8, Spencer F A. Arch Inter Med 168:425-430).
Medical textbooks and epidemiological studies characteristically consider arterial and venous thromboembolic disease as distinct entities, each with their own pathophysiological basis, unique risk factors, and distinct therapeutic regimens (Bauer K A. Hematology Am Soc Hematol Educ Program 2002;353-368). Arterial clots typically occur in an injured vessel and the most common cause of vascular damage in the arterial system is atherosclerotic vascular disease (AVD) (Lane D E 2000. Thromb Haemost 2000;76:651-62). The risk factors for arterial thrombosis are therefore considered the same as those for AVD. Arterial clots occur in a high flow, high shear environment and these clots, also called white clots, are rich in platelets. Prevention and treatment of arterial thrombosis is often aimed at platelet inhibition. While vascular injury can promote the formation of venous clots, stasis and changes in blood composition (thrombophilia) are the most important risk factors for venous clot development (Lane D E 2000. Thromb Haemost 2000;76:651-62). Venous clots occur in a low flow system, they are rich in fibrin that is enmeshed with red blood cells and are referred to as red clots. Inhibition of fibrin formation is the mainstay of prevention and treatment of venous thrombosis. It is often reported that the risk factors for arterial and venous thrombosis largely differ (Bauer K A. Hematology Am Soc Hematol Educ Program 2002;353-368).
However, recent studies have demonstrated a close association between arterial and venous thrombosis at a variety of levels. Specifically it has been shown that:    1) arterial and venous thrombosis share common risk factors (Doggen C J M Arteroscler Thromb Vasc Biol 2004;24:1970-5, Goldhaber S Z In: Bloom A L, Forbes C D, Thomas D P, Tuddenham E G D, eds. Hemostasis and Thrombosis. New York: Churchill and Livingstone: 1997;1327-1333),    2) individuals who suffer idiopathic venous thromboembolism are at a markedly increased risk of suffering a significant cardiovascular event (Becattini C. European Heart Journal 2005;26:77-83),    3) individuals who suffer idiopathic venous thromboembolism have an increased incidence of atherosclerotic vascular disease (Becattini C. European Heart Journal 2005;26:77-83),and    4) those who suffer idiopathic venous thromboembolism have a significantly higher incidence of metabolic syndrome (Ageno W. J Thromb Haemost 2006;4:1914-8).
The risk factors reported to be common to both arterial and venous thrombosis and that represent significant hazard for the development of each entity include increasing age and weight, smoking, exposure to estrogens, and the presence of diabetes. It has also been shown that high HDL cholesterol levels are associated with a decreased risk of venous thrombosis while elevated triglyceride and/or total cholesterol levels convey an increased risk. Other risk factors reported to be common to both arterial and venous thrombosis include the presence of antiphospholipid antibodies, dysfibrinogenemia, hyperhomocysteinemia, and elevated levels of fibrinogen, lipoprotein (a) and factor VIII.
One of the strongest pieces of evidence in favour of a link between arterial and venous thrombosis is the Genetic Analysis of Idiopathic Thrombophilia (GAIT) Study (Souto J C. Am J Hum Genet 2000:67:1452-1459). This family-based study of the genetics of thrombosis in a Spanish population was initiated to determine the heritability of thrombosis. Three hundred and twenty-eight individuals in 21 extended pedigrees were evaluated using a novel computer assisted adaptation of a multivariate threshold model. The authors concluded that more than 60% of the variation in susceptibility to common thrombosis is attributable to genetic factors. What makes this study unusual is that both venous and arterial thromboembolic events were included in the analysis. When venous and arterial thrombosis were jointly analyzed, arterial and venous thromboses were highly genetically correlated. That is, many of the same genes are involved in the pathogenesis of arterial and venous disease.
There are also studies (Doggen C J M, Smith N L, Lamahre R N, et al. Arteros Thromb Vasc Biol 2004;24:1970-5; Becattini E. European Heart Journal 2005;26:77-83; Ageno W.] Thromb Haemost 4:1914-8) suggesting that arterial and venous thrombosis represent different manifestations of the same disease and that the underlying process is driven by a common set of genes.
A) Prevention of First Episode of Thromboembolism
Symptomatic thrombosis (arterial o venous) is a multifactorial disease that manifests when a person with an underlying predisposition to thrombosis (thrombophilia also referred to as thrombophilic disorder or hypercoagulable syndromes) is exposed to clinical risk factors.
Assessment of presence of thrombophilia is not solely confined to laboratory testing but begins with a detailed history and physical examination. Detailed inquiry into symptoms and signs of acquired risk factors (coexisting diseases, medication exposure, and clinical circumstances) that are associated with thrombosis are an important part of the initial evaluation as is a complete physical examination. In addition to judicious laboratory testing appropriate for the patient's age and symptoms, objective confirmation of venous thromboembolism is critical.
Laboratory Testing
Currently, there is no single laboratory global assay that will ‘screen’ for the presence of thrombophilia. Thus, laboratory testing can be broadly categorized into (1) general diagnostic testing, (2) specialized coagulation testing, and (3) ancillary testing for disorders known to predispose to thrombotic disorders.
Specialized Coagulation Testing
Special Coagulation testing consists of a battery of complex (protein and DNA-based) thrombophilia assays to detect presence of an inherited or acquired thrombophilia. However, multiple preanalytical conditions affect results of the non-DNA-based assays (e.g. anticoagulants, acute thrombosis, liver disease, etc), so interpretation of results needs to be done within the context of the circumstances surrounding testing. An additional factor affecting the yield of testing is the ethnicity of the patient population being studied. Prevalence of factor V Leiden (FVL) varies from 3% to 7% in Caucasians of European ancestry, but has a very low prevalence in individuals of other ethnic groups: 0% among Native Americans/Australians and Africans, 0.16% among the Chinese, and 0.6% among individuals from Asia Minor (India, Pakistan, Sri Lanka). The ethnicity is important especially when few (one or two) genetic markers are analysed.
Factors Affecting Results of Protein-Based Specialized Coagulation Testing.
Effect of Acute Thrombosis
During the acute thrombotic episode, levels of antithrombin, protein C, and protein S may be transiently reduced; thus, if testing is not repeated, remote from the thrombotic event and from anticoagulant therapy, the patient may be misdiagnosed as having a congenital deficiency.
Effect of Anticoagulants
                Heparin. Heparin therapy can falsely reduce antithrombin levels. Although most lupus anticoagulant (LAC) reagents [e.g. dilute russel viper venom time (DRVVT) and Stadot APTT] contain heparin neutralizers that can neutralize up to 1 U/mL of heparin, presence of excess heparin may result in a false-positive test result, which impacts the duration of secondary prophylaxis. Thus, positive results of LAC testing performed while on heparin should be reconfirmed when the patient is off heparin.        Vitamin K antagonist (VKA) therapy. Protein C and S levels are lowered by VKA therapy (e.g. warfarin since they are vitamin K-dependent proteins). In addition, VKA therapy may result in a false-positive LAC with certain assays (e.g. DRVVT).        Direct thrombin inhibitors (DTIs; e.g. argatroban, lepirudin, bivalirudin). Because the majority of anticoagulant activity assays rely on generation of thrombin to achieve an endpoint of dot detection, presence of DTIs interfere with this endpoint and delay dot formation. This can lead to a false-positive LAC or falsely reduced protein C and S levels. Results of chromogenic assays are likely reliable.Effect of Liver Disease        
The majority of anticoagulant and procoagulant proteins are produced in the liver. In advanced liver disease, levels of both the anticoagulant and procoagulant proteins are reduced.
Sample Collection and Processing Issues
Practically speaking, ordering physicians have limited impact on specimen collection and processing; however, knowledge of such effects may lead one to consider repeat testing, if the data are unexpected or do not fit the expected pattern [e.g. reduced activated protein C resistance (APC-R) ratio suggesting presence of APC-R, yet the FVL test is negative].                Effect of Type of Anticoagulant in Specimen Collection Tube        
Standard specimen collection tubes contain 0.105-0.109 mol citrate for optimal results. Specimens may inadvertently be collected in ethylenediaminetetraacetic acid (EDTA), which will result in falsely reduced protein levels and a reduced APC-R ratio.                Effect of Specimen Processing        
Specimens should be double centrifuged as soon as possible after collection in order to reduce the amount of residual platelets to a minimum. The presence of residual platelets can result in a false-negative test for LAC.
Molecular Risk for Thrombotic Disease
Although an inherited tendency for excessive bleeding is often be ascribed to single or few gene abnormalities, there is ample evidence to suggest that, in contrast, the clinical manifestations of hypercoagulability are usually the result of adverse interactions between multiple genes and the environment. Thus, the use of molecular diagnostics to document markers of thrombotic risk (thrombophilia) will prove to be far more challenging than with the inherited hemorrhagic disorders. To further complicate matters, despite the fact that with appropriate testing, thrombophilic mutations can be identified in patients following a first clinical episode of venous thromboembolism, interpretation of these results remains problematic.
Inherited Resistance to Activated Protein C: Factor V Leiden
Until 1994, the investigation of patients with clinical evidence of hypercoagulability was usually unproductive. However, with the discovery by Dahlback and Hildebrand of an inherited form of resistance to the proteolytic effects of activated protein C, and the subsequent finding of a common missense mutation in the factor V gene by Bertina and colleagues in Leiden, a major advance was made in the laboratory assessment of thrombotic risk.
The Leiden mutation substitutes a glutamine for an arginine at amino acid residue 506 in factor V, the initial cleavage site for activated protein C. The mutation is readily detected by a number of PCR-based approaches. Between 2% and 5% of individuals in Western populations have been documented to be heterozygous for factor V Leiden. In contrast, the mutation is extremely rare in subjects of Asian and African descent.
In some laboratories, initial screening for resistance to activated protein C is performed using the prolongation of an activated partial thromboplastin time-based assay as an indicator; patients testing positive (prolongation in the presence of factor V-deficient plasma) are subsequently evaluated by a PCR.
Increasingly, where access to PCR-based molecular analysis is routine, laboratories will more often choose to proceed directly to the genetic test, as the result is definitive and more than 95% of activated protein C resistance is a result of this single mutation.
Persons heterozygous for the factor V Leiden mutation have an approximately five-fold increased relative risk of venous thrombosis. It is found in 15-20% of patients experiencing their first episode of venous thrombosis. The hypercoagulable phenotype associated with factor V Leiden shows incomplete penetrance, and some individuals may never manifest a clinical thrombotic event. In contrast to the increased relative risk for an initial venous thrombotic event associated with factor V Leiden, this genetic variant is not associated with increased risks for either arterial thrombosis or a recurrence of venous thrombosis. Coinheritance of other inherited thrombotic risk factors or exposure to environmental risk factors can dramatically enhance the thrombotic risk in carriers of factor V Leiden. Many clinicians test for this disorder in patients with a family history of thrombosis who are about to be exposed to an acquired thrombotic risk factor. Individuals homozygous for the mutation have a 70-fold enhanced relative risk of venous thrombosis, indicating that this phenotype is transmitted as a codominant trait.
Prothrombin 20210 3′ Non-Coding Sequence Variant
In 1996, Poort and colleagues described an association between a G to A nucleotide polymorphism at position 20210 in the 3′ untranslated region (UTR) of the prothrombin gene, increased plasma levels of prothrombin, and an enhanced risk for venous thrombosis. This polymorphic nucleotide substitution is at the very end of the 3′ UTR and exerts its effect on prothrombin levels in the heterozygous state. Although the plasma levels of prothrombin in subjects heterozygous for this polymorphism are higher on average than those in individuals with a normal prothrombin genotype, levels are usually still within the normal range. As a consequence, this polymorphism can only be evaluated by genetic testing, which is achieved by a PCR-based assay, most often now involving a form of real-time quantitative assay.
As with the factor V Leiden genotype, the prevalence of the prothrombin 20210 G to A variant in the general population is relatively high at 1-5%. This variant is also rare in persons of Asian and African descent. The heterozygous state is associated with a two-to four-fold increase in the relative risk for venous thrombosis. There is no influence on venous thrombotic recurrence. The relationship of prothrombin G2010A with arterial thrombosis is very modest (OR 1.32; 95% CI 1.03-1.69) (Kim R J. Am Heart J 2003;146:948-957).
Thermolabile C671T 5,10-Methylene-Tetrahydrofolate Reductase Variant
The third, high-prevalence gene tic variant that was initially thought to be associated with an increased thrombotic risk is the C to T variant at nucleotide 677 (an alanine to valine substitution) in the 5,10-methylene-tetrahydrofolate reductase (MTHFR) gene. This genotype results in expression of an enzyme with increased thermolability. Homozygosity for the variant is associated with hyperhomocysteinemia, particularly in the presence of folate deficiency. In many populations (southern Europeans and Hispanic Americans), approximately 10% of subjects are homozygous for the C677T variant, a sequence change that can easily be detected by a PCR-based strategy. However, after further extended analysis, in contrast to the factor V Leiden and prothrombin 20210 variants, the role of the MTHFR C677T polymorphism as an independent risk factor for venous thromboembolism appears minor.
B) Diagnosis of Venous Thromboembolism
Objective testing for deep vein thrombosis and pulmonary embolism is essential because clinical assessment alone is unreliable. Failure to diagnose venous thromboembolism is associated with a high mortality, whereas inappropriate anticoagulation can lead to serious complications, including fatal haemorrhage.
Diagnosis of Deep Vein Thrombosis
The clinical features of deep vein thrombosis include localized swelling, erythema, tenderness, and distal edema. However, these features are nonspecific, and approximately 85% of ambulatory patients with suspected deep vein thrombosis will have another cause for their symptoms. The differential diagnosis for deep vein thrombosis includes:                cellulites;        ruptured Baker cyst;        muscle tear, muscle cramps, muscle hematoma;        external venous compression;        superficial thrombophlebitis; and        post-thrombotic syndrome.Venography        
Venography is the reference standard test for the diagnosis of deep vein thrombosis. It has advantages over other tests in that it is capable of detecting both proximal vein thrombosis and isolated calf vein thrombosis. However, the disadvantages are that it:                is invasive, expensive, and requires technical expertise; and        exposes patients to the risks associated with contrast media, including the potential for an allergic reaction or renal impairment.        
For these reasons, noninvasive tests such as venous ultrasonography and D-dimer testing, alone or in combination with clinical assessment, have largely replaced venography.
Compression Venous Ultrasonography
This is the noninvasive method of choice for diagnosing DVT. The common femoral vein, superficial femoral vein, popliteal vein, and proximal deep calf veins are imaged in real time and compressed with the transducer probe. Inability 10 compress the vein fully is diagnostic of venous thrombosis. Venous ultrasonography is highly accurate for the detection of proximal vein thrombosis with a sensitivity of approximately 97%, specificity of approximately 94%, and negative predictive value of approximately 98% in symptomatic patients. If DVT cannot be excluded by a normal proximal venous ultrasound in combination with other results (e.g. low clinical probability or normal D-dimer), a follow-up ultrasound is performed after 1 week to check for extending calf vein thrombosis (present in approximately 2% of patients). If the second ultrasound is normal, the risk of symptomatic VTE during the next 6 months is less than 2%.
The accuracy of venous ultrasonography is substantially lower if its findings are discordant with the clinical assessment and/or if abnormalities are confined to short segments of the deep veins. Ideally, these patients should have a venogram because the result of the venogram will differ from the venous ultrasound in approximately 25% of these cases. If venography is not available, additional testing (e.g. D-dimer, serial venous ultrasonography) may help to clarify the diagnosis and avoid inappropriate anticoagulant therapy.
Venous ultrasonography of the calf veins is more difficult to perform (e.g. sensitivity 70%), and its value is controversial. Some investigators have proposed that a single complete compression ultrasound that includes examination of the calf veins should be used to exclude DVT. Studies using this method have reported an incidence of VTE of 0.5% during 3 months follow-up after a negative examination, establishing that a negative venous ultrasound that includes the calf veins excludes VTE [8]. However, this method has the potential to diagnose calf DVT that would have spontaneously lysed without treatment and to yield false-positive results, thereby exposing patients to the risk of bleeding due to anticoagulant therapy without clear benefit.
D-Dimer Blood Testing
D-dimer is formed when cross-linked fibrin is broken down by plasmin, and levels are usually elevated with DVT and/or PE. Normal levels can help to exclude VTE, but elevated D-dimer levels are non-specific and have low positive predictive value. D-dimer assays differ markedly in their diagnostic properties for VTE. A normal result with a very sensitive D-dimer assay (i.e. sensitivity of approximately 98%) excludes VTE on its own [i.e. it has a high negative predictive value (NPV). However, very sensitive D-dimer tests have low specificity (approximately 40%), which limits their use because of high false positive rates. In order to exclude DVT and/or PE, a normal result with a less sensitive D-dimer assay (i.e. approximately 85%) needs to be combined with either a low clinical probability or another objective test that has a high NPV, but is non-diagnostic on its own (e.g., negative venous ultrasound of the proximal veins. As less sensitive D-dimer assays are more specific (approximately 70%), they yield fewer false-positive results.
Specificity of D-dimer decreases with aging and with comorbid/illness, such as cancer. Consequently, D-dimer testing may have limited value as a diagnostic test for VTE in hospitalized patients (more false positive results) and is unhelpful in the early postoperative period.
Computed Tomographic (CT) Venography and Magnetic Resonance (MR) Venography
CT venography and MR venography have the potential to diagnose DVT in settings where the accuracy of compression ultrasonography is limited (e.g. isolated pelvic DVT, asymptomatic patients). The sensitivity and specificity of CT venography compared with compression ultrasonography for detecting all DVT has been reported between 89% and 100%, and 94% and 100%, respectively. However, given the cost, exposure to radiation, and limited availability of CT venography, this modality currently plays a limited role in the diagnosis of DVT. A meta-analysis of studies comparing MR venography with conventional venography reported a pooled sensitivity of 92% and specificity of 95% of MR venography for proximal DVT. As with CT venography, cost and availability will inhibit the widespread use of MR for diagnosis of acute DVT.
Diagnosis of Pulmonary embolism (PE)
The clinical features of PE may include:                pleuritic chest pain,        shortness of breath.        syncope.        hemoptysis, and        palpitations.        
As with DVT, these features are non-specific, and objective testing must be performed to confirm or exclude the diagnosis of PE.
Pulmonary Angiography
This is the reference standard test for the diagnosis of PE. However, it has many of the same limitations as venography.
Computed Tomographic Pulmonary Angiography (CTPA)
Spiral CT (also know as helical CT) with peripheral injection of radiographic contrast (CTPA) is the current standard diagnostic test for PE (Stein P D. N Engl J Med 2006;354:2317-2327, Roy P M. Br Med J 2005;331:259). In comparison with ventilation-perfusion lung scanning, CTPA is less likely to be “non-diagnostic” (i.e. approximately 10% vs. 60%) and has the potential to identify an alternative etiology for the patient's symptoms. This technique has a sensitivity of 83%, specificity of 96%, NPV of 95%, and positive predictive value of 86% for PE.
Accuracy of CTP A varies according to the size of the largest pulmonary artery involved and according to clinical pretest probability. For example, the positive predictive value of CTPA is 97% for pulmonary emboli in the main or lobar artery, but drops to 68% for segmental arteries, and is lower still for PE in the subsegmental arteries (25%). In patients with a high clinical pretest probability of PE, the positive predictive value of CTPA is 96%, but this value falls to 92% in patients with a technical pretest probability of PE, and to 58% in patients with a low clinical pretest probability of PE.
In management studies that used CTP A to diagnose PE, less than 2% of patients who had anticoagulant therapy withheld based on a negative CTPA went on to have symptomatic VTE during follow-up. Taken together, these observations suggest the following:                A good-quality, normal CTPA excludes PE if clinical suspicion is low or moderate.        Lobar or larger pulmonary artery intraluminal defects are generally diagnostic for PE.        Segmental pulmonary artery intraluminal defects are generally diagnostic for PE if clinical suspicion is moderate or high, but should be considered non-diagnostic if suspicion is low or there are discordant findings (e.g. negative D-dimer).        Subsegmental pulmonary artery intraluminal defects are nondiagnostic, and patients with such findings require further testing.        
A note of caution: If possible, CTPA should be avoided in younger women (e.g. younger than 40 years) because it delivers a substantial dose of radiation to the chest, which increases the risk of breast cancer.
Ventilation-Perfusion Lung Scanning
In the past, ventilation-perfusion lung scanning was the initial investigation in patients with suspected PE, and it is still useful in patients with contraindications to x-ray contrast dye (e.g. renal failure) and patients at higher risk for developing breast cancer from radiation exposure (e.g. young women). A normal perfusion scan excludes PE, but is only found in a minority of patients (10-40%). Perfusion defects are non-specific; only approximately one-third of patients with perfusion defects have PE. The probability that a perfusion defect is caused by PE increases with size and number and the presence of a normal ventilation scan (“mismatched” defect). A lung scan with mismatched segmental or larger perfusion defects is termed “high-probability.” A single mismatched defect is associated with a prevalence of PE of approximately 80%. Three or more mismatched defects are associated with a prevalence of PE of approximately 90%. Lung scan findings are highly age-dependent, with a relatively high proportion of normal scans and a low proportion of non-diagnostic scans in younger patients. A high frequency of normal lung scans is also seen in pregnant patients who are investigated for PE.
Clinical Assessment:
As with suspected DVT, clinical assessment is useful for categorizing probability of PE.
D-Dimer Testing:
As previously discussed when considering the diagnosis of DVT, a normal D-dimer result, alone or in combination with another negative test, can be used to exclude PE.
Patients with Nondiagnostic Combinations of Noninvasive Tests for PE
Patients with non-diagnostic test results for PE at presentation have a prevalence of PE of approximately 20%; therefore, further investigations to exclude PE are required.
Diagnosis of PE in Pregnancy
Pregnant patients with suspected PE can be managed similarly to non-pregnant patients, with the following modifications:                Venous ultrasound of the legs should be performed first followed by ventilation-perfusion lung scanning if there is no DVT.        The amount of radioisotope used for the perfusion scan should be reduced and the duration of scanning extended.        If pulmonary angiography is performed, the brachial approach with abdominal screening is preferred.        The use of CTPA in pregnancy is discouraged, primarily because of radiation exposure to the mother.C) Risk of Recurrence after a First Episode of Symptomatic Venous Thromboembolism        
Venous thromboembolism is associated with diverse risk factors, some of which are transient, such as recent surgery and pregnancy, and others of which are persistent, such as cancer (Table 1 shows the risk factors for venous thromboembolism). When venous thromboembolism is associated with an acquired risk factor, either transient or persistent, it is called provoked. When there is no apparent clinical risk factor, it is called unprovoked or idiopathic.
TABLE 1Risk factors for venous thromboembolismMajor transient risk factorsHospitalizationPlaster cast immobilizationSurgeryTraumaMinor transient risk factorsOral contraceptives or hormone therapyPregnancyPresence of major risk factors 1 to 3months before venous thromboembolismProlonged travel (≧2 hours)Potential acquired or persistent riskfactorsCollagen vascular diseasesHeart failureMalignancyMedicationsMyelo proliferative disordersNephrotic syndrome
It has recently been recognized that the presence or absence of a transient, or reversible, risk factor at the time of venous thromboembolism strongly affects the risk of recurrence after anticoagulant therapy is stopped. Patients with venous thromboembolism provoked by a transient risk factor have a low risk of recurrence compared with patients with either venous thromboembolism provoked by a persistent risk factor or unprovoked venous thromboembolism (Alfonso Iorio. Arch Intern Med 2010;170:1710-1716). For this reason, patients with venous thromboembolism provoked by a transient risk factor are usually treated with anticoagulant agents for 3 months (Alfonso Iorio. Arch Intern Med 2010;170:1710-1716), whereas patients with venous thromboembolism that was not associated with a transient risk factor are often treated long-term (Alfonso Iorio. Arch Intern Med 2010;170:1710-1716). The cumulative risk of recurrence at one, five, and 10 years is 15, 41, and 53 percent, respectively, in patients with an idiopathic venous thromboembolism, compared with 7, 16, and 23 percent in patients with a provoked event (Galioto N J. Am Fam Physician 2011;83:293-300).
Although it is widely accepted that the risk of recurrence in patients with venous thromboembolism provoked by a transient risk factor is low enough to justify stopping anticoagulant therapy after 3 months, this recurrence risk is not well quantified. Furthermore, the risk of recurrence may not be the same in all patients with venous thromboembolism provoked by a transient risk factor.
D) Risk for Arterial Thrombosis
Arterial thrombosis is a common cause of hospital admission, death, and disability in developed countries (and increasingly in developing nations because of global epidemics of smoking, obesity, and diabetes). It usually follows spontaneous rupture of an atherosclerotic plaque, and may:                Be clinically silent;        Contribute to atherosclerotic progression resulting in coronary stenosis and stable angina, or lower limb artery stenosis and claudication:        Be present as acute ischemia in the heart (acute coronary syndromes: unstable angina, myocardial infarction), brain (transient cerebral ischemic attack or stroke), or lim (acute limb ischemia).        
Traditional risk factors (see table 2) remain the most important markers of arterial disease.
TABLE 2Risk factorsDyslipemiaCurrent smokerDiabetesHypertensionAbdominal obesityPsychosocial factors
The factor V Leiden and prothrombin G20210A mutations show modest but statistically significant associations with coronary heart disease, stroke, and peripheral arterial events, specially in younger persons (age under 55 years) and in women. The relationship of prothrombin G2010A with arterial thrombosis is very modest (OR 1.32; 95% Cl 1.03-1.69) (Kim R J. Am Heart J 2003;146:948-957). The relationship of factor V Leiden mutation and arterial ischemic events is also modest (OR 1.21; 95% Cl 0.99-1.49), patients <55 years old were at greater risk for arterial ischemic event (OR 1.37;95% CI 0.96-1.97) (Kim R J. Am Heart J 2003;146:948-957).
There is little evidence that other congenital thrombophilias are associated with increased risk of arterial disease.
Need for New Risk Factors
Despite the above mentioned existence of risk factors and diagnostic tools for early diagnosis arterial thrombosis and venous thromboembolism, which includes deep vein thrombosis and pulmonary embolism, are major causes of morbidity and mortality.
Even among high-risk groups it is not possible to identify individuals who will go on to develop thrombosis and/or venous thromboembolism. Therefore, although several strategies exist for both precise the identification of the risk to develop a thromboembolic event, its prevention or the precise diagnosis of a thromboembolic disease, the goal of preventing the clinical burden of thrombosis and/or thromboembolism has not yet been accomplished (Ruppert A. Current Medical Research & Opinion 2010;26:2465-2473).
Several attempts have been done to use molecular diagnostics to identify subjects at high risk to develop a trombotic and/or thromboembolic event. Starting from the finding of a common missense mutation in the factor V gene by Bertina (Bertina R M. Nature 1994;369:64-67), the description of the prothrombin 20210 3′ non-coding sequence variant (Poort S R. Blood 1996;88:3698-3703), and the thermolabile C677T 5,10-methylene-tetrahydrofolate reductase variant. There is also patent document such as EP00696325B1 describing the use of mutations in coagulation factors. EP00696325B1 describes the use of mutations in factor V to identify persons at risk to develop thrombotic event. Or the patent document WO05047533A1 describing a method for detecting the presence or absence of a variant nucleotide in at least two SNP sites associated with thrombosis, said SNP sites selected from the group consisting of factor V Leiden G1691A, Prothrombin (Factor II) G20210A, MTHRF C677T, MTHFR A1298C, factor XIII G4377T, and tissue factor plasma inhibitors (TFPI) C536T.
However, none of the attempts tried until now have proved satisfactory efficacy and the initial enthusiasm for test adoption will need to be tempered by formal evidence of clinical benefit deriving from the test.
Accordingly, there is a need for novel markers, including new genetic markers and specific combinations thereof that would successfully and advantageously predict who is at high risk of developing a thromboembolic disease and/or thromboembolic disease complications such as—but not limited to—deep vein thrombosis, pulmonary embolism, acute coronary syndromes (acute myocardial infarction, unstable angina), stroke, transient ischemic attack or stroke in a way that preventive measures could be implemented to keep that risk at the lowest possible level.
There is also a need for novel markers, including new genetic markers and specific combinations thereof that would successfully and advantageously assist the diagnosis of a thromboembolic disease and/or thromboembolic disease complications such as—but not limited to—deep vein thrombosis, pulmonary embolism, acute coronary syndromes (acute myocardial infarction, unstable angina), stroke, transient ischemic attack or stroke in a way that preventive measures could be implemented to keep that risk at the lowest possible level.
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