Editor's Choice – European Society for Vascular Surgery (ESVS) 2021 Clinical Practice Guidelines on the Management of Venous Thrombosis

American College of Chest Physicians adjusted hazard ratio activated protein C antiphospholipid antiphospholipid syndrome activated partial thromboplastin time antithrombin Acute Venous Thrombosis: Thrombus Removal with Adjunctive Catheter-Directed Thrombolysis arteriovenous fistula body mass index CAtheter Versus Anticoagulation Alone for Acute Primary Iliofemoral DVT Catheter-Directed Venous Thrombolysis in Acute Iliofemoral Vein Thrombosis cancer associated venous thrombosis catheter directed thrombolysis confidence interval chronic kidney disease computed tomography creatinine clearance catheter related thrombosis computed tomography venography compression ultrasound scanning central venous catheter chest X ray Duration of Anticoagulation based on Compression UltraSonography Disabilities of the Arm, Shoulder and Hand direct oral anticoagulant deep vein thrombosis electrocardiogram elastic compression stockings European Society for Vascular Surgery European Union Guidelines Committee great saphenous vein Guideline Writing Committee heparin induced thrombocytopenia hazard ratio international normalised ratio inferior vena cava international unit intravenous low molecular weight heparin multilayer bandaging magnetic resonance imaging magnetic resonance venography number needed to treat odds ratio prothrombin complex concentrate pulmonary embolism pharmacomechanical catheter directed thrombolysis platelet factor 4 paroxysmal nocturnal haemoglobinuria Prospective Observational Superficial Thrombophlebitis post-thrombotic syndrome quality of life randomised controlled trial relative risk recombinant tissue plasminogen activator residual venous obstruction summary of product characteristics small saphenous vein superficial vein thrombosis Thrombus Obliteration by Rapid Percutaneous Endovenous Intervention in Deep Venous Occlusion upper extremity deep vein thrombosis unfractionated heparin vitamin K antagonist venous thromboembolism whole leg ultrasound Dedication These guidelines are dedicated to the memory of Dr Clive Kearon of McMaster University in Hamilton, Ontario, Canada. Dr Kearon extensively reviewed the first and second versions of the manuscript and he was always very punctual. In the first review round he submitted a review of 16 pages with many detailed and helpful comments. Unaware of his illness, we invited him to review the final version of the guidelines on June 2, 2020, but sadly he passed away one day later, on June 3, 2020. We will always remember Dr Kearon for his many contributions to the field of Thrombosis and Antithrombotic Treatment, including these guidelines. (picture reproduced with permission from Weitz JI & Bates SM. Obituary for Dr. Clive Kearon. J Thromb Haemost. 2020;18:2783–2784). The European Society for Vascular Surgery (ESVS) has developed a series of clinical practice guidelines for the care of patients with vascular diseases. Their aim is to assist clinicians in selecting the best management strategies to achieve optimal patient outcomes. These are the first ESVS guidelines on venous thrombosis. In 2017, the ESVS Guidelines Committee (GC), initiated a process to develop these guidelines. The present guideline document addresses acute deep vein thrombosis (DVT) of the lower extremity (unless otherwise stated), upper extremity DVT (UEDVT), superficial vein thrombosis (SVT), and thrombosis in unusual sites. The guideline document also covers topics in addition to treatments, including investigations and health economics, and includes special patient populations. The topic of venous thrombosis is large and therefore the remit of the guideline has been limited to conditions and situations likely to be commonly encountered by clinical teams/end users managing patients with venous thrombosis and others exposed to this condition. Furtheremore, all recent ESVS guidelines have considered the patient’s perspective.1Björck M. Earnshaw J.J. Acosta S. Bastos Gonçalves F. Cochennec F. Debus E.S. et al.Editor's Choice – European Society for Vascular Surgery (ESVS) 2020 Clinical Practice Guidelines on the Management of Acute Limb Ischaemia.Eur J Vasc Endovasc Surg. 2020; 59: 173-218Abstract Full Text Full Text PDF PubMed Scopus (22) Google Scholar,2Wanhainen A. Verzini F. Van Herzeele I. Allaire E. Bown M. Cohnert T. et al.Editor's Choice – European Society for Vascular Surgery (ESVS) 2019 Clinical Practice Guidelines on the Management of Abdominal Aorto-iliac Artery Aneurysms.Eur J Vasc Endovasc Surg. 2019; 57: 8-93Abstract Full Text Full Text PDF PubMed Scopus (393) Google Scholar This guideline document was written and approved by the 16 members of the Guideline Writing Committee (GWC). The GWC consisted mainly of ESVS members, and also eminent thrombosis experts from other societies with relevant clinical experience, strong publication records, and academic profiles. The recommendations in this guideline have been formulated by evaluation of the available scientific evidence, with expert opinion to create pragmatic guidance for patient management. The recommendations represent the best available knowledge at the time of publication. However, as technology, available evidence, and disease knowledge may evolve rapidly, recommendations can become outdated. It is the aim of the ESVS to update the guidelines when important new insights into the evaluation and management of venous thrombosis become available. Although guidelines have the purpose of promoting best practice according to specialists in the field, this guideline document should not be seen as the legal standard of care for all patients with venous thrombosis. The document provides guiding principles and pragmatic recommendations to aid clinical decision making. However, the care given to an individual patient may be dependent on many factors, including symptoms, comorbidities, age, level of activity, treatment setting, available techniques, local expertise, and other considerations. Members of this GWC were selected by the two chairs and approved by the ESVS GC to represent physicians involved in the management of patients with venous thrombosis. The members of the GWC have provided disclosure statements stating all relationships that might be perceived as potential conflicts of interest. These disclosure forms are kept on file at the ESVS headquarters. The ESVS GC was responsible for the overall process of endorsing this guideline. All expert members involved in the GWC have contributed to and approved the final document. The guideline document underwent a formal external expert peer review process, and, additionally, was reviewed and approved by the ESVS GC and by the editors of the European Journal of Vascular and Endovascular Surgery. This document was reviewed over three rounds by 18 reviewers, including 11 members of GC (with a review coordinator) and seven external reviewers from Europe and the USA. All reviewers assessed all versions and approved the final version of this document. The first GWC meeting was held in May 2018, in Brussels. The table of contents and overall structure of the guideline document was discussed and agreed. Tasks and activities required to create the guideline were evaluated and distributed between GWC members. Contributions from GWC members were compiled into a draft guideline by the co-chairs. At a second meeting, held in Frankfurt in February 2019, the wording/grading of each suggested recommendation was reviewed. If unanimous agreement was not present, reasons for disagreement were discussed and the wording, grade, and level of evidence were amended to try and reach a consensus. If this failed, then the wording, grade, and level of evidence was secured via a majority vote of GWC members. The final version of the guideline was accepted on August 2020. In response to changes in the available evidence and knowledge, it is intended that these guidelines will be updated periodically. Members of the committee, supported by clinical librarians if necessary, performed a literature search for this guideline in MEDLINE (through PubMed), Embase, and clinical trial databases, and the Cochrane Library up to 31 March 2018. Reference checking and hand searches by individual GWC members added other relevant evidence and literature. Additional relevant references were considered and included as GWC members became aware of them. A second formal literature search for papers published between April 2018 and August 2019 was performed in August 2019. Members of the GWC performed the literature selection based on the information provided in the title and abstract of the retrieved studies. Criteria for search and selection were (1) English language; (2) level of evidence: when considering which published evidence to include, the literature was considered following the accepted hierarchy of evidence, with priority given to aggregated evidence (meta-analyses), followed by randomised controlled trials (RCTs), then observational studies (the level of available evidence for each section was used to guide the class of each recommendation in the guideline); (3) sample size: larger studies were given more weight than smaller studies; and (4) relevant articles published after the final literature search (August 2019) or in another language were included, but only if they were considered to be of paramount importance to this guideline. To define the current guidelines, members of the GWC reviewed and summarised the relevant peer reviewed published literature. Conclusions were drawn based on the available scientific evidence. In keeping with other published ESVS guidelines, the clinical practice recommendations in this document are presented using the European Society of Cardiology grading system. For each recommendation, the letter A, B, or C indicates the level of current evidence guiding the recommendation (Table 1).Table 1Levels of evidenceLevel of evidence AData derived from multiple randomised clinical trials or meta-analysesLevel of evidence BData derived from a single randomised clinical trial or large non-randomised studiesLevel of evidence CConsensus of experts opinion and/or small studies, retrospective studies, and registries Open table in a new tab Depending on whether the recommendation is strongly supportive of an intervention, weakly supportive, or strongly against an intervention, each recommendation is categorised as either Class I, IIa/IIb, and III, respectively (Table 2). The lower the class number, the greater the evidence and/or general agreement in favour of an intervention.Table 2Classes of recommendationsClass of recommendationDefinitionClass IEvidence and/or general agreement that a given treatment or procedure is beneficial, useful, and effectiveClass IIConflicting evidence and/or a divergence of opinion about the usefulness/efficacy of the given treatment or procedure Class IIa Weight of evidence/opinion is in favour of usefulness/efficacy Class IIb Usefulness/efficacy is less well established by evidence/opinionClass IIIEvidence or general agreement that the given treatment or procedure is not useful/effective, and in some cases may be harmful Open table in a new tab The importance of patient and public involvement in clinical guideline development is widely recognised and accepted. Patient and public engagement improves validity, increases quality of decisions, and is encouraged by national and international societies. In order to improve accessibility and interpretability for patients and the public, a plain English summary was produced for this guideline and subjected to a lay review process. Information for patients was drafted for each subchapter which was read and amended by a vascular nurse specialist and one lay person. Lay summaries were evaluated by eight patients with a history of venous thrombosis in the UK National Health Service and four lay members of the public without venous thrombosis. For all patients and members of the public asked to scrutinise the lay summary, the background and rationale for the ESVS venous thrombosis guidelines was explained. Honest feedback was encouraged on any aspect of the summary. The feedback was collated, and several themes were identified. Firstly, both patients and lay members of the public recognised the importance of venous thrombosis and welcomed the engagement. Several respondents commented that other conditions seemed to get much more public attention than venous thrombosis. All respondents acknowledged the importance of anticoagulant medication and appreciated that significant advances had been made with the widespread use of direct oral anticoagulants (DOACs). Most feedback related to the use of interventions to reduce long term sequelae of venous thrombosis, particularly compression and early thrombus removal strategies for upper and lower extremity DVT. All respondents offered positive feedback about compression therapy, with the majority of patients with a history of venous thrombosis stating that this was not offered to them at the time of the initial presentation. They appreciated that the recommendations were based on the latest published evidence but expressed that even if the benefit was uncertain or modest, it should be discussed with future patients. Clinical teams managing patients with venous thrombosis should consider this feedback and ensure that potential interventions are discussed with patients and the rationale for offering or not offering early thrombus removal is clearly explained to the patient. Feedback from the focus group was used to amend and improve the clarity of the lay summaries. The annual incidence of first episode of symptomatic DVT in the adult population ranges from 50 to 100 per 100 000 population, with the overall incidence of venous thromboembolism (VTE) around 25% higher with the addition of pulmonary embolism (PE) events.3Heit J.A. Spencer F.A. White R.H. The epidemiology of venous thromboembolism.J Thromb Thrombolysis. 2016; 41: 3-14Crossref PubMed Scopus (312) Google Scholar,4Spencer F.A. Emery C. Joffe S.W. Pacifico L. Lessard D. Reed G. et al.Incidence rates, clinical profile, and outcomes of patients with venous thromboembolism. The Worcester VTE study.J Thromb Thrombolysis. 2009; 28: 401-409Crossref PubMed Scopus (143) Google Scholar Published epidemiology studies are either retrospective, using national or regional patient cohorts studied over several years, or prospective ultrasound based studies performed over 1 – 2 years.5Baekgaard N. Incidence and location of deep vein thrombosis in the lower extremities: what do we know?.Plebolymphology. 2017; 24: 97-104Google Scholar The incidence of DVT is slightly greater in women aged 20 – 45 years, but men have a higher incidence between 45 and 60 years of age.3Heit J.A. Spencer F.A. White R.H. The epidemiology of venous thromboembolism.J Thromb Thrombolysis. 2016; 41: 3-14Crossref PubMed Scopus (312) Google Scholar,6Silverstein M.D. Heit J.A. Mohr D.N. Petterson T.M. O'Fallon W.M. Melton III, L.J. Trends in the incidence of deep vein thrombosis and pulmonary embolism: a 25-year population-based study.Arch Intern Med. 1998; 158: 585-593Crossref PubMed Scopus (1988) Google Scholar The incidence is higher for males for all age groups if female specific risk factors (oral contraceptives and pregnancy) are excluded.7Roach R.E. Cannegieter S.C. Lijfering W.M. Differential risks in men and women for first and recurrent venous thrombosis: the role of genes and environment.J Thromb Haemost. 2014; 12: 1593-1600Crossref PubMed Scopus (26) Google Scholar The incidence increases twofold per 10 year age increase. At least one in 12 middle aged adults will develop either DVT and/or PE in their remaining lifetime and 60% of all VTE events occur in patients aged > 65 years.3Heit J.A. Spencer F.A. White R.H. The epidemiology of venous thromboembolism.J Thromb Thrombolysis. 2016; 41: 3-14Crossref PubMed Scopus (312) Google Scholar,8Bell E.J. Lutsey P.L. Basu S. Cushman M. Heckbert S.R. Lloyd-Jones D.M. et al.Lifetime risk of venous thromboembolism in two cohort studies.Am J Med. 2016; 129: 339.e19-339.e26Abstract Full Text Full Text PDF PubMed Google Scholar African Americans have a higher incidence of DVT than Caucasians and Native Americans, whereas Asians (China and Korea) have a lower incidence. A seasonal variation occurs, with a higher incidence of VTE in the winter, peaking in February.9Dentali F. Ageno W. Rancan E. Donati A.V. Galli L. Squizzato A. et al.Seasonal and monthly variability in the incidence of venous thromboembolism. A systematic review and a meta-analysis of the literature.Thromb Haemost. 2011; 106: 439-447Crossref PubMed Scopus (70) Google Scholar The rate of recurrent VTE is around 10% the first year and 30% after 5 – 8 years for patients with unprovoked DVT with an unidentified triggering factor (see also Table 13, Table 14).10Khan F. Rahman A. Carrier M. Kearon C. Weitz J.I. Schulman S. et al.Long term risk of symptomatic recurrent venous thromboembolism after discontinuation of anticoagulant treatment for first unprovoked venous thromboembolism event: systematic review and meta-analysis.BMJ. 2019; 366: l4363Crossref PubMed Scopus (35) Google Scholar The annual incidence of VTE has not changed in the last two to three decades, although the prevalence of cancer, major surgery, trauma, and obesity has increased, and the widespread availability of improved diagnostic modalities with computed tomography (CT) and magnetic resonance imaging (MRI) leading to increased detection of incidental VTE in patients with cancer.11Heit J.A. Ashrani A. Crusan D.J. McBane R.D. Petterson T.M. Bailey K.R. Reasons for the persistent incidence of venous thromboembolism.Thromb Haemost. 2017; 117: 390-400Crossref PubMed Scopus (42) Google Scholar DVT is considered unprovoked if no clear precipitating risk factor can be identified. Risk factors are either hereditary or more often acquired. For provoked DVT, risk factors include cancer, acute medical illness, surgery, trauma, immobility (often in hospital and lasting at least three days), obesity, inflammatory diseases/infection, hormone therapy (oestrogen containing), pregnancy (particularly the postpartum period), long distance travel, recent hospitalisation, and antiphospholipid syndrome (APS). Primary varicose veins constitute a minor risk factor only. More recently, prolonged computer related “seated immobility syndrome” has also been recognised as a potential risk factor.12Braithwaite I. Healy B. Cameron L. Weatherall M. Beasley R. Venous thromboembolism risk associated with protracted work- and computer-related seated immobility: a case–control study.JRSM Open. 2016; 72054270416632670Crossref Google Scholar The most common inherited risk factor is a non-O blood type, which is associated with double the risk of VTE.13Franchini M. Mannucci P.M. ABO blood group and thrombotic vascular disease.Thromb Haemost. 2014; 112: 1103-1109Crossref PubMed Scopus (67) Google Scholar Another common thrombophilia is heterozygous factor V Leiden gene polymorphism, which may increase the risk of VTE by a factor of 3 – 8 in selected populations. Severe thrombophilia comprising homozygous factor V Leiden, deficiency of antithrombin, protein C or protein S, and APS increases the risk of DVT by a factor of 20 – 80.14Olaf M. Cooney R. Deep venous thrombosis.Emerg Med Clin North Am. 2017; 35: 743-770Abstract Full Text Full Text PDF PubMed Scopus (16) Google Scholar Important risk factors for arterial thromboembolism such as hypertension and diabetes are also risk factors for VTE, but their significance is far less prominent.15Gaertner S. Cordeanu E.M. Mirea C. Frantz A.S. Auger C. Bilbault P. et al.Increased risk and severity of unprovoked venous thromboembolism with clustering cardiovascular risk factors for atherosclerosis: results of the REMOTEV registry.Int J Cardiol. 2018; 252: 169-174Abstract Full Text Full Text PDF PubMed Scopus (7) Google Scholar For patients with cancer, an externally validated clinical prediction model incorporating D dimer and only one clinical factor (tumour site category) has been shown to predict the risk of VTE.16Pabinger I. van Es N. Heinze G. Posch F. Riedl J. Reitter E.M. et al.A clinical prediction model for cancer-associated venous thromboembolism: a development and validation study in two independent prospective cohorts.Lancet Haematol. 2018; 5: e289-e298Abstract Full Text Full Text PDF PubMed Scopus (77) Google Scholar The precise cause of DVT is likely to vary from patient to patient, but the main pathophysiological factors implicated in thrombosis are considered to be increased procoagulant activity in the blood, vein wall damage, and impaired venous flow (Virchow’s triad). Impaired flow, known also as venous stasis, may result from external compression by aneurysms, tumours, or the right common ilac artery, which compresses and causes fibrosis of the underlying left common iliac vein in May–Thurner syndrome (iliac vein compression syndrome). The thrombotic process leads to increased outflow resistance and decreased outflow volume with increased venous pressure, which, together with perivascular inflammation, is responsible for the characteristic symptoms and signs of DVT. Patients suffer swelling, pain, and tenderness, usually in the calf, but symptoms may also involve the thigh in the case of iliofemoral DVT. The symptoms typically diminish as the inflammatory reaction decreases and usually disappear if the veins can recanalise fully without structural damage to the vein wall or damaged valves. The recanalisation rate is around 80% in calf veins but only 20% in the iliac segments. Prolonged venous obstruction may result in chronic venous outflow obstruction and secondary venous valve damage, causing reflux after recanalisation. Venous obstruction, reflux, or a combination may lead to the development of post-thrombotic syndrome (PTS).17Lee B.B. Nicolaides A.N. Myers K. Meissner M. Kalodiki E. Allegra C. et al.Venous hemodynamic changes in lower limb venous disease: the UIP consensus according to scientific evidence.Int Angiol. 2016; 35: 236-352PubMed Google Scholar The first signs of PTS usually develop within three months of the onset of DVT, and PTS symptoms and signs may progress and deteriorate for years.18Kahn S.R. Comerota A.J. Cushman M. Evans N.S. Ginsberg J.S. Goldenberg N.A. et al.The postthrombotic syndrome: evidence-based prevention, diagnosis, and treatment strategies: a scientific statement from the American Heart Association.Circulation. 2014; 130: 1636-1661Crossref PubMed Scopus (250) Google Scholar The most extreme clinical presentation of DVT may occur when there is occlusion of the common femoral and external iliac veins, completely obstructing the outflow of all deep and superficial veins of the limb, as well as collaterals, and is termed phlegmasia cerulea dolens (see Chapter 2.10). Anticoagulation therapy is used to reduce the risk of PE and prevent the progression of DVT. However, resolution of thrombus is dependent on the endogenous fibrinolytic activity in the affected veins. Symptoms and signs are generally more severe as the thrombosis extends more proximally, reflecting the greater degree of outflow obstruction and haemodynamic disturbance. Among the three anatomical types of DVT, i.e., iliofemoral, femoropopliteal, and calf DVT (see Chapter 2.2.2.1), iliofemoral DVT tends to be associated with the most severe symptoms. Symptoms from calf DVT may vary, and even be asymptomatic, depending on the collateral drainage. It should be noted that up to 80% of DVT cases may not be clinically apparent, with pain being the only feature. In DVT cases located at iliofemoral level the leg is usually considerably swollen and painful, with decreased mobility and oedema from the groin and distally due to limited venous collateral drainage in the pelvic region. Prominent superficial veins may be seen. For DVT originating in the iliac veins, back pain may be an early feature. Several lower extremity disorders may mimic DVT. These include lymphoedema, SVT, PTS, cellulitis, ruptured Baker cyst, and trauma.19Meissner M.H. The clinical presentation and natural history of acute deep venous thrombosis.in: Gloviczki P. Handbook of venous and lymphatic disorders. 4th edn. CRC Press, Boca Raton, FL2017: 205-219Crossref Google Scholar Isolated calf DVT is seen in approximately 30% and thrombosis involving the iliofemoral segment accounts for around 30%.20Partsch H. Therapy of deep vein thrombosis with low molecular weight heparin, leg compression and immediate ambulation.Vasa. 2001; 30: 195-204Crossref PubMed Google Scholar,21De Maeseneer M.G. Bochanen N. van Rooijen G. Neglen P. Analysis of 1,338 patients with acute lower limb deep venous thrombosis (DVT) supports the inadequacy of the term "proximal DVT".Eur J Vasc Endovasc Surg. 2016; 51: 415-420Abstract Full Text Full Text PDF PubMed Google Scholar Iliofemoral DVT is more commonly left sided, probably owing to the frequent compression of the left common iliac vein by the overriding right common iliac artery.21De Maeseneer M.G. Bochanen N. van Rooijen G. Neglen P. Analysis of 1,338 patients with acute lower limb deep venous thrombosis (DVT) supports the inadequacy of the term "proximal DVT".Eur J Vasc Endovasc Surg. 2016; 51: 415-420Abstract Full Text Full Text PDF PubMed Google Scholar The financial burden of DVT and PE is substantial owing to the treatment costs related to DVT (inpatient or outpatient treatment, re-admission/recurrence) or PE (additional costs for re-admission/recurrence), costs related to complications of treatment, including bleeding and heparin induced thrombocytopenia (HIT), and costs related to long term complications, including PTS and chronic thromboembolic pulmonary hypertension.22Barco S. Woersching A.L. Spyropoulos A.C. Piovella F. Mahan C.E. European Union-28: an annualised cost-of-illness model for venous thromboembolism.Thromb Haemost. 2016; 115: 800-808Crossref PubMed Scopus (29) Google Scholar A health economic modelling study using 2014 values estimated that annual total costs may range from €1.5 to €13.2 billion for the 28 member states of the European Union (EU).22Barco S. Woersching A.L. Spyropoulos A.C. Piovella F. Mahan C.E. European Union-28: an annualised cost-of-illness model for venous thromboembolism.Thromb Haemost. 2016; 115: 800-808Crossref PubMed Scopus (29) Google Scholar The same study estimated that preventable costs may range from €0.5 to €7.3 billion, implying that better prophylaxis, optimisation of outpatient treatment, and earlier hospital discharge of patients with PE and DVT may result in cost savings. Another recent review investigated the economic burden of VTE healthcare costs in the USA.23Grosse S.D. Nelson R.E. Nyarko K.A. Richardson L.C. Raskob G.E. The economic burden of incident venous thromboembolism in the United States: a review of estimated attributable healthcare costs.Thromb Res. 2016; 137: 3-10Abstract Full Text Full Text PDF PubMed Scopus (123) Google Scholar For 375 000 – 425 000 newly diagnosed VTE events per annum in the USA, a conservative cost estimate for medical treatment to the healthcare system was $7 – $10 billion each year, a much higher cost than for the EU.23Grosse S.D. Nelson R.E. Nyarko K.A. Richardson L.C. Raskob G.E. The economic burden of incident venous thromboembolism in the United States: a review of estimated attributable healthcare costs.Thromb Res. 2016; 137: 3-10Abstract Full Text Full Text PDF PubMed Scopus (123) Google Scholar Several clinical features are known to be suggestive of DVT. These comprise symptoms, signs, and other clinical risk factors. Although useful to raise the clinical suspicion of DVT, these factors cannot be used individually to confirm or exclude the diagnosis. However, when incorporated in decision tools, an individualised pre-test probability of DVT can be assigned to patients, aiding decision making strategies.24Goodacre S. Sampson F. Stevenson M. Wailoo A. Sutton A. Thomas S. et al.Measurement of the clinical and cost-effectiveness of non-invasive diagnostic testing strategies for deep vein thrombosis.Health Technol Assess. 2006; 10: 1-168Crossref PubMed Google Scholar,25Stevens S.M. Ageno W. Review: the Wells rule is more useful than individual clinical features for predicting risk of deep venous thrombosis.Evid Based Med. 2006; 11: 56Crossref PubMed Scopus (0) Google Scholar The most thoroughly studied and validated clinical decision score is the Wells DVT score (Table 3), which categorises the pre-test probability scores of DVT into two (DVT likely if score ≥ 2 or unlikely if score < 2) or three groups (high likelihood of DVT if ≥ 3; moderate likelihood if 1 – 2; low likelihood if ≤ 0).26Wells P.S. Owen C. Doucette S. Fergusson D. Tran H. Does this patient have deep vein thrombosis?.JAMA. 2006; 295: 199-207Crossref PubMed Scopus (257) Google Scholar The dichotomised Wells score is simpler and more widely used than the Wells three category version and significant advantages to stratification into three groups have not been demonstrated. Although the Wells DVT score is useful, the probability of DVT in the low risk group has been reported to be as high as 5%.25Stevens S.M. Ageno W. Review: the Wells rule is more useful than individual clinical features for predicting risk of deep venous thrombosis.Evid Based Med. 2006; 11: 56Crossref PubMed Scopus (0) Google Scholar With this risk of a false negative result, the score cannot be used as a standalone test to confirm or exclude DVT. However, when used in conjunction with additional investigations, namely D dimer measurements and/or ultrasound, it is a valuable tool for accurate decision making.27Geersing G.J. Zuithoff N.P. Kearon C. Anderson D.R. Ten Cate-Hoek A.J. Elf J