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The warning signs of deep vein thrombosis

The warning signs of deep vein thrombosis

Key learning points:

–    Symptoms of deep vein thrombosis can be minimal but a patient will typically complain of unilateral leg pain and swelling

–    Hospitalisation increases the risk and extended thromboprophylaxis is given to high-risk patients on discharge

–    Once a deep vein thrombosis is suspected, an ultrasound scan should be performed within four hours

A deep vein thrombosis (DVT) is a thrombus (blood clot) that has developed in the venous system, most commonly in the deep veins of the leg, and can partially or completely obstruct the flow of blood. If not treated, a DVT can break off and travel through the veins and heart to the pulmonary arteries in the lungs. This is known as a pulmonary embolism (PE) and can be fatal.

The term venous thromboembolism (VTE) is used to describe a blood clot that can either be a DVT or a PE. Standard treatment for VTE is with anticoagulant drugs such as warfarin.

DVT is common; one person in every 1,000 is affected each year.1 Factors contributing to the development of thrombosis were first identified in the 19th Century and are known as Virchow’s triad, which consists of:

            – Damage to the vessel wall.

            – Alterations in blood flow.

            – Hypercoagulability of the blood.

Thrombus formation is activated by damage to the vessel wall and the slow flow of blood as this causes platelets to stick to the vessel wall. Platelet aggregation then activates a sequence of events involving coagulation factors, fibrin strands, platelets and red cells to form a fibrin clot (thrombus).2

Risk factors

Primary care nurses are ideally placed to not only identify the signs and symptoms of DVT, but they can also instigate further urgent assessment and investigations for those patients at risk. Early identification and treatment of a DVT may prevent the development of a pulmonary embolism.

Risk factors for DVT are not always present but common risk factors for the development of DVT include:

            – Trauma and surgery, which can cause damage to veins and disrupt the flow of blood in the legs, this is what happened to John (see Case Study).

            – Heart failure, long-distance travel and bed rest can result in venous stasis and will alter the flow of blood in the veins. Community nurses monitoring patients with heart failure should be aware of a sudden increase in breathlessness or the development of unilateral leg swelling.

            – Pregnancy and childbirth can cause damage to blood vessels and alterations in blood flow. Hypercoagulablity of the blood due to hormonal changes occurs to prevent severe haemorrhage during labour and up to six weeks post-partum. Patients are now routinely advised of this risk and may seek advice from a community nurse.

            – Cancer can cause a hypercoagulable state as tumour cells can activate coagulation factors. Tumours can also press on veins and alter blood flow. Chemotherapy can further increase the risk of DVT by causing damage to the endothelial lining of the veins. Cancer patients need to be informed that signs of a DVT require urgent assessment and cannot wait until the next routine appointment.

            – The risk of DVT goes up with age – one in every 100 people aged over 80 is affected.

Hospitalisation increases the risk of DVT tenfold1 and nearly two thirds of all VTE episodes are associated with hospitalisation.3 Extended mechanical or pharmacological thromboprophylaxis is now routinely prescribed for up to one month to high-risk patients as the risk of VTE continues after hospitalisation.

Healthcare professionals can encourage patients to comply with these measures and explain the importance of wearing stockings, keeping mobile and hydrated to reduce the risk of VTE.

High-risk patients include those who have had major cancer surgery in the abdomen or surgery for hip fractures, and patients undergoing hip and knee replacements. Thromboprophylaxis is also given to high-risk obstetric patients. In addition, all hospitalised patients are given written and verbal information on admission, and discharge notes about VTE prevention and are informed to seek urgent medical advice if they develop signs of DVT or PE.4

John (see Case Study) had completed his 10 days of oral thromboprophyaxis and was aware of the signs and symptoms of a DVT and where to seek urgent advice.

Presentation of DVT

Symptoms can be minimal but a patient with a DVT will typically complain of unilateral leg pain and swelling.

Examination of the affected leg may reveal a tight calf and pitting oedema, both caused by the thrombus obstructing venous blood flow in the leg. Thrombus obstructing the deep veins may lead to the development of a collateral circulation and dilated superficial veins may be visible. Erythema and an increase in temperature, particularly at the back of the calf, may also be present.

Once a DVT is suspected a physical examination, combined with a clinical history, should be performed to assess the patient and help rule out alternative causes of lower limb swelling, which include a ruptured Baker’s cyst, cellulitis and a calf haematoma.5


All patients who present with symptoms should be assessed using the two-level DVT Wells score to determine clinical probability of the condition.

The assessment can be done in primary care by a nurse practitioner or a GP. If it is not possible to perform the assessment in primary care the patient should have an urgent assessment at hospital. High-risk patients should be referred to their nearest VTE clinic for further assessment and investigation.

The score helps to stratify patients into ‘DVT unlikely’ and ‘DVT likely’ groups and is used in conjunction with a D-dimer blood test. The D-dimer test measures fibrin degradation and is raised in the presence of an acute thrombosis. In the absence of a thrombosis, D-dimer levels are expected to be normal but can be raised when the coagulation factors are activated by recent surgery, pregnancy or infection.6 The D-dimer test is sometimes done in primary care by the assessing nurse but can also be done in hospital.

Patients with a likely two-level Wells DVT score (two points or above) should have a proximal leg vein ultrasound scan (USS) within four hours. If the result is negative, a D-dimer test should be performed.

If an USS cannot be carried out within four hours, the patient should have a D-dimer test and be given a therapeutic dose of a parenteral anticoagulant – usually low molecular weight heparin (LMWH). This is what happened to John (see Case Study) and he was informed that he received treatment for a suspected blood clot. Those with a negative USS and a raised D-dimer should be offered a rescan in six to eight days.

It is important that a suspected DVT is treated promptly to prevent potentially fatal thrombus extension. DVT of the lower limb usually starts in the calf veins and 10-20% will extend proximally with a further 1-5% of these patients developing a fatal PE. Anticoagulant therapy is used to reduce this complication.7

The patient should be informed of this and be aware to seek urgent medical advice if they develop signs of PE such as shortness of breath or chest pain while awaiting an USS.

DVT is considered unlikely in those with a two-level Wells DVT score of 1 point or less. These patients should be offered a D-dimer blood test and if the result is positive should have a proximal leg vein USS within four hours. If the scan cannot be carried out in this timeframe, a therapeutic dose of anticoagulation should be given while awaiting USS.

Patients in whom a DVT is considered unlikely, those with a low D-dimer or a negative USS should be advised of the signs and symptoms of PE and where to seek urgent medical advice.

Pulmonary embolism

Thrombus obstructing the pulmonary arteries will typically cause symptoms of pleuritic chest pain, shortness of breath and tachycardia.

A patient presenting with signs of DVT and PE requires urgent medical attention at a hospital. If untreated, 50% of proximal DVTs, those occurring in the popliteal vein or above, will embolise and develop into a PE.8

Treatment of DVT

DVT is treated with anticoagulants and this is started at the time of diagnosis. The aim of treatment is to prevent thrombus formation or extension of an existing thrombus, thereby reducing the risk of PE.

Treatment is usually on an outpatient basis and can be with warfarin and LMWH or with a direct oral anticoagulant (DOAC). DOACs were until recently called NOACs (novel oral anticoagulants).

The choice of anticoagulant should be discussed with the patient and their preferences and lifestyle should be taken into account. John (see Case Study) leads a busy life and felt that a DOAC would suit him best.

Primary care nurses are often involved in the monitoring of anticoagulants and are therefore ideally placed to inform patients of the importance of compliance and the different anticoagulants available.

LMWH acts within seconds, it is therefore given to patients when a DVT is suspected and the patient is awaiting further investigations. Fondaparinux is strictly not a heparin but is chemically related to heparins and works in a similar manner and can also be used.

The therapeutic effects of warfarin are usually seen after 24 to 36 hours, but the full effect might take several days, therefore LMWH needs to be started at the same time as warfarin and should be continued until therapeutic anticoagulation with warfarin is achieved. The effect of warfarin varies between individuals and can be influenced by diet and other medication and therefore requires careful monitoring and dose adjustments.

Therapeutic doses of DOACs can also be used for the treatment of DVT. All have a direct inhibitory action on the coagulation pathway with a rapid onset of action, and deliver consistent levels of anticoagulation without the need for monitoring.9


A diagnosis of DVT should be considered in any patient with unilateral lower limb pain and swelling. Prompt assessment taking into account risk factors and clinical signs will identify those at risk who require urgent further investigations. Primary care nurses are ideally placed to assess patients at risk as they are often the first point of contact for a patient.


1.         Scottish Intercollegiate Guidelines Network. Prevention and management of venous thromboembolism quick reference guide. (accessed on 21 February 2016).

2.         Kyrle P, Eichener S. Is Virchow’s triad complete? Blood 2009;114(6).

3.         Heit J, O’Fallon W, Petterson T, Lohse C, Silverstein M, Mohre D, Melton J. Relative impact of risk factors for deep vein thrombosis and pulmonary embolism: A population- based study. Arcives of Interal Medicine 2002;162(11):1245-1248.

4.         The National Institute for Health and Care Excellence. Venous thromboembolism: reducing the risk for patients in hospital, NICE guidelines [CG92].

            (accessed on 21 February 2016).

 5.        The National Institute for Health and Care Excellence. Venous thromboembolic disease: diagnosis, management and thrombophilia testing. (accessed on 21 February 2016).

6.         Factors associated with positive D-dimer results in patients evaluated for pulmonary Embolism. Academic Emergency Medicine 2010;17(6):589-597.

7.         Turpie A, Chin B, Lip G. Venous thromboembolism: pathophysiology, clinical features and prevention. British Medical Journal 2002; 325:887-890.

8.         Riedel M. Acute pulmonary embolism 1: Pathophysiology, clinical presentation and diagnosis. Heart 2001;85:229-240.

9.         British National Formulary. (2015-2016) British National Formulary British Medical Journal group and pharmaceutical press.

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