Deep Vein Thrombosis (DVT)

Definition

Deep vein thrombosis (DVT) is the formation of a blood clot (thrombus) within a deep vein, most often in the calf, thigh or pelvis. Together with its main complication, pulmonary embolism (PE), it makes up venous thromboembolism (VTE). Distal (calf) and proximal (popliteal and above) DVT behave differently and are managed differently — proximal clot carries the substantially higher risk of embolism.

Pathophysiology

Clot formation is classically explained by Virchow's triad: stasis of blood flow, vessel wall injury, and increased clotting tendency. A thrombus forming in a deep vein obstructs venous return, causing local swelling and pain, and can propagate proximally; if a fragment breaks free it travels through the venous system and right heart to lodge in the pulmonary arteries.

Two longer-term consequences follow from the same process. The thrombus organises and the vein recanalises imperfectly, leaving valve damage and chronic venous hypertension — the basis of post-thrombotic syndrome. And in a minority, unresolved pulmonary clot organises into fibrous tissue, producing chronic thromboembolic pulmonary hypertension.

Co-morbidities

DVT risk rises with active cancer, prior VTE, obesity, heart failure, inflammatory conditions, and inherited or acquired clotting disorders (Factor V Leiden, antiphospholipid syndrome). Chronic venous insufficiency and post-thrombotic syndrome can follow a DVT and cause ongoing leg symptoms. Reduced mobility from any cause — neurological, orthopaedic or respiratory — compounds every other risk factor.

Prevalence

VTE affects roughly 1–2 people per 1,000 each year and becomes markedly more common with age, hospitalisation, surgery and cancer. It is a leading preventable cause of hospital-associated death, which is why formal risk assessment and prophylaxis are now routine on admission.¹

Causes and risk factors

• Immobility — hospital admission, long-haul travel, prolonged bed rest or reduced mobility after surgery or injury.
• Surgery and trauma, especially major orthopaedic and abdominal/pelvic surgery.
• Active cancer and some cancer treatments.
• Pregnancy and the postpartum period, and oestrogen-containing contraception or hormone therapy.
• Inherited or acquired thrombophilia and a personal or family history of VTE.
• Obesity, older age, and central venous catheters.

A DVT is classed as provoked when a transient risk factor explains it and unprovoked when none is found. This distinction is not academic — it determines how long anticoagulation continues.¹

Symptoms

Typical features

Unilateral leg swelling, pain or tenderness (often in the calf), warmth and redness, and sometimes visibly distended surface veins. Symptoms can be subtle or absent entirely, and severity does not track clot size.

What DVT can resemble

Calf strain, ruptured Baker's cyst, cellulitis, superficial thrombophlebitis and post-operative swelling all mimic it. This is directly relevant to physiotherapy: a calf that is swollen, warm and disproportionately painful after immobility or surgery is not a muscle tear to be treated until DVT has been excluded.

Warning signs of pulmonary embolism

Diagnosis

Why diagnosis matters

Untreated proximal DVT carries a significant risk of embolism, while anticoagulating someone who does not have one exposes them to avoidable bleeding. The diagnostic pathway exists to resolve that quickly rather than to treat on suspicion.

How is it diagnosed?

Clinical probability is estimated first using a validated score such as the Wells score, which determines what happens next. In low-probability patients a negative D-dimer safely excludes DVT without imaging; in higher-probability patients D-dimer is unhelpful and imaging is required regardless.²

Compression ultrasound

Compression ultrasound of the leg veins is the primary imaging test — a vein that fails to compress under the probe contains thrombus. Where an initial scan is negative but suspicion remains, it is repeated after about a week to catch a propagating calf clot.

When pulmonary embolism is also suspected

CT pulmonary angiography is the usual test. Because DVT and PE are the same disease in two places, confirming either one is generally enough to start treatment for both.³

Investigations for related conditions

An unprovoked DVT prompts consideration of occult malignancy and, in selected patients, thrombophilia testing — though testing rarely changes immediate management and is best deferred until after the acute phase.³

Management

Management and goals

The goals are to stop the clot propagating, prevent embolism, relieve symptoms, and reduce the risk of recurrence and post-thrombotic syndrome — while keeping bleeding risk acceptable.³

Anticoagulation

Anticoagulation is the mainstay, usually a direct oral anticoagulant (DOAC) started promptly once DVT is confirmed. Rivaroxaban⁴ and apixaban⁵ were both shown to be non-inferior to conventional heparin-plus-warfarin treatment with less major bleeding, and DOACs are now first-line for most patients. Low molecular weight heparin remains preferred in pregnancy and in some cancer-associated thrombosis.

How long treatment continues

A minimum of three months, extended where risk factors persist or the clot was unprovoked, with the decision reviewed periodically against bleeding risk rather than set once and forgotten.³

Compression

Graduated compression stockings relieve swelling and discomfort in the acute phase. Their role in preventing post-thrombotic syndrome is less certain than was long assumed — a large placebo-controlled trial found no benefit for that specific endpoint — so they are offered for symptom relief rather than promised as prevention.⁶

Thrombolysis and clot retrieval

Reserved for extensive, limb-threatening iliofemoral clot. Catheter-directed thrombolysis reduced post-thrombotic syndrome at two years in one trial⁷ but a larger trial found no reduction in post-thrombotic syndrome overall and more major bleeding, with benefit limited to reducing severity in iliofemoral disease.⁸ It is therefore a selective intervention, not a routine one.

Early mobilisation

Once anticoagulated and clinically stable, walking and early mobilisation are encouraged. Compression with walking reduces pain and swelling faster than bed rest,⁹ and pooled data show early ambulation does not increase the incidence of pulmonary embolism.¹⁰ Bed rest for DVT is an outdated practice that causes harm through deconditioning without conferring protection.

Identifying deterioration

Increasing leg pain or swelling despite treatment, new breathlessness or pleuritic chest pain, or any bleeding — visible, or signalled by dizziness, black stools or unexplained bruising — all need urgent review.

Action plan

1. Take the anticoagulant exactly as prescribed, at the same time each day; missed doses matter more with DOACs than with warfarin because they are short-acting.
2. Keep moving. Walk regularly and avoid prolonged sitting or bed rest.
3. Seek emergency care for sudden breathlessness, chest pain, coughing blood or collapse.
4. Report any significant bleeding, or a fall or head injury while anticoagulated.
5. Tell every clinician, dentist and surgeon that you are anticoagulated, before any procedure.
6. Do not stop anticoagulation for surgery on your own — it is planned with the prescribing team.

Medications

Anticoagulant choice

DOACs (rivaroxaban, apixaban and others) are first-line for most people, given orally with no routine monitoring.^4,5 Warfarin is still used where a DOAC is unsuitable — severe renal impairment, antiphospholipid syndrome, mechanical valves — and requires INR monitoring. Low molecular weight heparin is used in pregnancy and in some cancer settings.

Duration and bleeding risk

Extended anticoagulation reduces recurrence but raises bleeding risk, and the balance is individual. Some patients continue on a reduced maintenance dose long term.³

Around surgery and procedures

Interruption for surgery is planned in advance by the prescriber, with the timing set by the drug, renal function and the bleeding risk of the procedure. This is a common point of error and worth confirming rather than assuming.³

Multi-system manifestations

Lungs

Pulmonary embolism is the immediate danger. In a small proportion, unresolved clot organises and causes chronic thromboembolic pulmonary hypertension (CTEPH) — persisting exertional breathlessness months after a VTE is not simply slow recovery and warrants investigation, because CTEPH is potentially curable by surgery.

The affected limb

Up to a third develop some degree of post-thrombotic syndrome — chronic swelling, aching, heaviness, skin pigmentation and, in severe cases, venous ulceration. A six-month exercise training programme improves symptoms and quality of life in established post-thrombotic syndrome, making this a genuinely treatable condition rather than an inevitable residue.¹¹

Occult malignancy

Unprovoked VTE is sometimes the first sign of an undiagnosed cancer, which is why age-appropriate screening and a careful history form part of follow-up.

Consequences of treatment

Anticoagulation carries its own systemic risk — gastrointestinal and intracranial bleeding above all. This shapes physiotherapy practice directly: falls prevention becomes a bleeding-prevention intervention, and head injury in an anticoagulated patient is always urgent.

Living with deep vein thrombosis

Activity and exercise

Most people resume normal activity within days of starting anticoagulation. Walking, cycling and general conditioning are encouraged; there is no requirement to protect the leg by resting it.⁹ Contact and collision sport is the exception while anticoagulated, because of bleeding risk rather than clot risk.

Compression garments

Where stockings are used for symptom relief, fit and correct application matter more than compression class, and a garment that is painful or rolls down will not be worn.⁶

Travel

On long journeys, move regularly, stay hydrated, and use calf exercises; people with prior VTE should discuss whether compression or prophylaxis is warranted before travelling.¹

Future surgery, pregnancy and hormones

Prior VTE changes prophylaxis planning for any future admission or pregnancy, and oestrogen-containing contraception is generally avoided afterwards. Carrying a card or note recording the event and its treatment makes this reliable rather than dependent on recall.³

Recurrence

Knowing the early symptoms of both DVT and PE, and acting on them promptly, is the most useful long-term self-management skill in this condition.

Prognosis

With prompt anticoagulation most people recover well and the acute clot resolves or is contained. Recurrence risk depends heavily on whether the event was provoked or unprovoked, and guides duration of treatment. Up to a third develop some degree of post-thrombotic syndrome, though its severity is modifiable with exercise and compression rather than fixed at the outset.¹¹

Role of the physiotherapist

Physiotherapy has three distinct jobs in DVT, and one of them is diagnostic:

• Recognition. Physiotherapists frequently see the swollen, painful calf first — after surgery, during an admission, or in outpatient practice. Withholding treatment and escalating for assessment is the correct action, and treating a suspected DVT as a soft-tissue injury is a serious error.
• Early mobilisation. Once anticoagulated and stable, walking and progressive activity are encouraged rather than feared; bed rest offers no protection against embolism and causes measurable harm.^9,10
• Longer-term rehabilitation. Structured exercise improves established post-thrombotic syndrome,¹¹ and physiotherapy also addresses the surgery, illness or immobility that caused the DVT in the first place, and reinforces prevention — calf exercises, hydration and movement breaks — for people at ongoing risk.

Physiotherapy red flags — stop and escalate: new unilateral calf swelling, warmth or disproportionate pain; sudden breathlessness or pleuritic chest pain; haemoptysis; and, in anticoagulated patients, any head injury, fall or unexplained bleeding.

Part 1 · References

1. Schünemann HJ, Cushman M, Burnett AE, et al. American Society of Hematology 2018 guidelines for management of venous thromboembolism: prophylaxis for hospitalized and nonhospitalized medical patients. Blood Adv 2018;2(22):3198–3225.
2. Wells PS, Anderson DR, Rodger M, et al. Evaluation of D-dimer in the diagnosis of suspected deep-vein thrombosis. N Engl J Med 2003;349(13):1227–1235.
3. Stevens SM, Woller SC, Kreuziger LB, et al. Antithrombotic therapy for VTE disease: second update of the CHEST guideline and expert panel report. Chest 2021;160(6):e545–e608.
4. EINSTEIN Investigators. Oral rivaroxaban for symptomatic venous thromboembolism. N Engl J Med 2010;363(26):2499–2510.
5. Agnelli G, Buller HR, Cohen A, et al. Oral apixaban for the treatment of acute venous thromboembolism (AMPLIFY). N Engl J Med 2013;369(9):799–808.
6. Kahn SR, Shapiro S, Wells PS, et al. Compression stockings to prevent post-thrombotic syndrome: a randomised placebo-controlled trial (SOX). Lancet 2014;383(9920):880–888.
7. Enden T, Sændsøy NR, Kløw NE, et al. Long-term outcome after additional catheter-directed thrombolysis versus standard treatment for acute iliofemoral deep vein thrombosis (CaVenT). Lancet 2012;379(9810):31–38.
8. Vedantham S, Goldhaber SZ, Julian JA, et al. Pharmacomechanical catheter-directed thrombolysis for deep-vein thrombosis (ATTRACT). N Engl J Med 2017;377(23):2240–2252.
9. Partsch H, Blättler W. Compression and walking versus bed rest in the treatment of proximal deep venous thrombosis with low molecular weight heparin. J Vasc Surg 2000;32(5):861–869.
10. Aissaoui N, Martins E, Mouly S, Weber S, Meune C. A meta-analysis of bed rest versus early ambulation in the management of pulmonary embolism, deep vein thrombosis, or both. Int J Cardiol 2009;137(1):37–41.
11. Kahn SR, Shrier I, Shapiro S, et al. Six-month exercise training program to treat post-thrombotic syndrome: a randomized controlled two-centre trial. CMAJ 2011;183(1):37–44.

References are numbered in citation order (Vancouver/BMJ style) and were current at the time of writing. Guidelines are living documents — verify against the latest version before clinical use.