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Diseases of the circulatory system

Deep vein thrombosis

Deep vein thrombosis (DVT) is the formation of a thrombus within a deep vein, most often in the lower extremity, that can obstruct venous return or embolize to the lungs. It typically affects adults with Virchow triad risk factors (stasis, endothelial injury, hypercoagulability) such as immobilization, surgery, or malignancy. The single most testable fact is that DVT is a major preventable cause of pulmonary embolism, so a positive Wells score plus elevated D-dimer should prompt compression ultrasound before anticoagulation.

Practice questionsHigh-yield facts
ICD-10I80.2
Typical patientPost-surgical or immobilized adult with unilateral leg swelling
Key findingUnilateral swelling, warmth, tenderness, dilated collateral veins (Homan sign unreliable)
First-line treatmentDirect oral anticoagulant (e.g., apixaban or rivaroxaban)
4 min readFor medical studentsUpdated 2026-10-14

Definition and epidemiology

Deep vein thrombosis is thrombus formation within the deep venous system, most commonly the proximal (femoral, popliteal) or distal (calf) veins of the lower extremity. Upper extremity DVT occurs less often, usually related to central venous catheters or thoracic outlet compression.

DVT and pulmonary embolism (PE) are considered a single disease spectrum, venous thromboembolism (VTE). Annual incidence is approximately 1 per 1,000 adults, rising sharply with age (over 1 per 100 in those older than 80). It is a leading cause of preventable in-hospital mortality worldwide.

  • Proximal DVT carries higher embolic risk than isolated distal (calf) DVT.
  • Recurrence risk is highest in the first 6-12 months after an unprovoked event.
High-yield for exams
  • Virchow triad: stasis, endothelial injury, hypercoagulability
  • Compression ultrasound is the first-line diagnostic test
  • D-dimer is sensitive but not specific; useful mainly to rule out low-probability DVT
  • Factor V Leiden is the most common inherited thrombophilia predisposing to DVT
  • DOACs (apixaban, rivaroxaban) are now first-line for most patients
  • Proximal DVT has higher PE risk than isolated distal DVT
  • Phlegmasia cerulea dolens is a surgical/vascular emergency
  • Unprovoked DVT should raise suspicion for occult malignancy

Etiology and risk factors

DVT arises from the classic Virchow triad: venous stasis, endothelial injury, and hypercoagulability.

Common risk factors

  • Surgery (especially orthopedic, pelvic) and trauma
  • Immobilization: prolonged bed rest, long-haul travel, hospitalization
  • Malignancy (active cancer, especially pancreatic, lung, gastric)
  • Pregnancy and the postpartum period
  • Estrogen therapy: oral contraceptives, hormone replacement
  • Inherited thrombophilia: factor V Leiden (most common), prothrombin G20210A mutation, protein C/S deficiency, antithrombin deficiency
  • Antiphospholipid syndrome
  • Obesity, smoking, central venous catheters, nephrotic syndrome

DVT occurring without an obvious provoking factor (unprovoked) warrants consideration of occult malignancy or thrombophilia, particularly if recurrent or in an unusual site.

Pathophysiology

Venous thrombi form predominantly in areas of low shear stress, such as venous valve pockets in the calf, where blood stasis allows activated clotting factors to accumulate rather than being washed away.

Endothelial injury or dysfunction exposes tissue factor and subendothelial collagen, triggering platelet adhesion and activation of the coagulation cascade. The resulting thrombus is a red (fibrin and red cell rich) thrombus, in contrast to the platelet-rich white thrombus of arterial disease.

As the clot propagates, it can occlude venous outflow, raising venous pressure distally and causing edema, pain, and skin changes. Fragments may dislodge and travel through the right heart to lodge in the pulmonary arteries, producing PE. Chronic venous valve damage after DVT leads to post-thrombotic syndrome.

Clinical features

Presentation ranges from asymptomatic to severe swelling, and clinical exam alone is unreliable for diagnosis.

  • Unilateral leg (calf or whole-limb) swelling
  • Pain or tenderness along the deep venous system
  • Warmth and erythema of the affected limb
  • Dilated superficial collateral veins
  • Homan sign (calf pain on forced dorsiflexion) — low sensitivity and specificity, not used for diagnosis
  • Phlegmasia cerulea dolens: massive iliofemoral thrombosis causing a painful, cyanotic, swollen limb (surgical emergency)

Always assess for signs of PE (dyspnea, chest pain, tachycardia, hypoxia) since DVT and PE frequently coexist.

Diagnosis

Diagnosis combines clinical pretest probability, D-dimer, and imaging.

Step-wise approach

  1. Calculate pretest probability using the Wells score for DVT.
  2. Low probability: obtain D-dimer. If negative, DVT is excluded. If positive, proceed to ultrasound.
  3. Moderate-to-high probability: proceed directly to compression (duplex) ultrasound, the primary imaging test.
  4. If ultrasound is negative but suspicion remains high, repeat ultrasound in 5-7 days or use venography/MR venography.
TestRole
D-dimerRules out DVT if negative and pretest probability is low; poor specificity
Compression ultrasoundFirst-line imaging; loss of vein compressibility is diagnostic
CT or MR venographyUsed for pelvic/IVC thrombosis or inconclusive ultrasound

D-dimer is nonspecific and elevated in pregnancy, malignancy, infection, and recent surgery, limiting its use in high pretest probability patients.

Differential diagnosis

  • Cellulitis
  • Ruptured Baker cyst
  • Muscle strain or hematoma (gastrocnemius tear)
  • Chronic venous insufficiency / post-thrombotic syndrome
  • Lymphedema
  • Superficial thrombophlebitis
  • Compartment syndrome (in trauma setting)

Management

Anticoagulation is the mainstay of treatment for proximal and most distal DVT.

Acute treatment

  • Direct oral anticoagulants (DOACs) such as apixaban or rivaroxaban are first-line per current CHEST (ACCP) and ASH guidance for most patients, given orally without routine monitoring.
  • Low molecular weight heparin (e.g., enoxaparin) is preferred in pregnancy and often in active cancer, though DOACs are increasingly used in cancer-associated thrombosis per updated guidelines.
  • Vitamin K antagonists (warfarin) remain an option, bridged with heparin, particularly where DOACs are unavailable or contraindicated (e.g., severe renal impairment, antiphospholipid syndrome).

Duration

  • Provoked (surgery, transient risk factor): typically 3 months.
  • Unprovoked first episode: at least 3 months, with extended or indefinite therapy considered after weighing bleeding risk and recurrence risk.
  • Active cancer or recurrent unprovoked VTE: extended, often indefinite anticoagulation.

Other measures

  • Compression stockings may reduce post-thrombotic syndrome symptoms, though evidence is mixed.
  • IVC filter: reserved for patients with a contraindication to anticoagulation or recurrent PE despite therapeutic anticoagulation.
  • Catheter-directed thrombolysis or thrombectomy: considered for phlegmasia cerulea dolens or extensive iliofemoral DVT threatening limb viability.
  • Isolated distal (calf) DVT without severe symptoms or risk factors for extension may be managed with serial ultrasound surveillance instead of anticoagulation in select low-risk patients, per some guideline bodies.

Complications and prognosis

  • Pulmonary embolism: the most feared acute complication, occurring in a substantial minority of untreated proximal DVT.
  • Post-thrombotic syndrome: chronic limb pain, swelling, skin changes, and ulceration from venous valve damage, affecting a significant proportion of patients within 1-2 years.
  • Recurrent VTE: risk is highest for unprovoked events and persistent risk factors such as active cancer.
  • Phlegmasia cerulea dolens and venous gangrene: rare but limb-threatening.

With timely anticoagulation, most patients recover well, though long-term venous valve dysfunction and recurrence risk require ongoing monitoring and risk-factor management.

Mnemonic

Virchow triad = 'SHE clots': Stasis, Hypercoagulability, Endothelial injury.

Practice questions

1. A 68-year-old man develops unilateral left calf swelling and tenderness 5 days after total hip replacement. Wells score is calculated as moderate probability. D-dimer is elevated. What is the most appropriate next step?

Answer: B. In a patient with moderate-to-high pretest probability, compression ultrasound is the appropriate next step regardless of D-dimer, since D-dimer is not useful to rule out DVT in this risk category. Ultrasound showing loss of vein compressibility would confirm the diagnosis before starting anticoagulation.

2. A 45-year-old woman with metastatic pancreatic cancer is diagnosed with proximal DVT. Which anticoagulation strategy is most consistent with current guideline recommendations for cancer-associated thrombosis?

Answer: C. Cancer-associated thrombosis is traditionally treated with low molecular weight heparin, though current guidelines now also support select DOACs in many cancer patients. Because active malignancy is an ongoing provoking factor, extended (often indefinite) anticoagulation is recommended rather than a fixed short course.

3. A 30-year-old woman presents with a painful, swollen, cyanotic left leg and absent pedal pulses. Imaging confirms extensive iliofemoral DVT. Which complication is of greatest immediate concern?

Answer: C. This presentation describes phlegmasia cerulea dolens, a limb-threatening complication of massive iliofemoral venous thrombosis causing venous outflow obstruction severe enough to compromise arterial inflow. It requires urgent vascular intervention such as catheter-directed thrombolysis or thrombectomy to prevent venous gangrene and limb loss.

Frequently asked questions

What causes deep vein thrombosis?

DVT is caused by a combination of venous stasis, vessel wall injury, and increased blood clotting tendency, known as the Virchow triad. Common triggers include surgery, prolonged immobilization, cancer, pregnancy, estrogen use, and inherited clotting disorders like factor V Leiden. Often more than one risk factor is present simultaneously, which is why hospitalized or post-surgical patients are at particularly high risk.

What are the first symptoms of DVT?

The earliest symptoms are usually unilateral calf or leg swelling, pain, and warmth, sometimes with visible redness or prominent surface veins. Symptoms can be subtle or absent in some patients, so clinical suspicion combined with risk factor assessment is important. Any new unilateral leg swelling, especially after surgery, travel, or immobilization, should prompt evaluation.

How is DVT diagnosed?

Diagnosis starts with a clinical probability score (Wells score), followed by D-dimer testing in low-probability patients or direct compression ultrasound in higher-probability patients. Ultrasound showing a non-compressible vein confirms the diagnosis. CT or MR venography is reserved for pelvic or inferior vena cava thrombosis or when ultrasound is inconclusive.

Is DVT curable?

DVT can resolve with appropriate anticoagulation, which prevents clot extension and embolization while the body naturally breaks down the thrombus over weeks to months. However, some patients develop long-term complications like post-thrombotic syndrome or remain at risk for recurrence, especially with ongoing risk factors such as active cancer. Lifelong management may be needed in select high-risk patients.

DVT vs superficial thrombophlebitis — what is the difference?

DVT involves clot formation in the deep venous system and carries a real risk of pulmonary embolism, requiring anticoagulation. Superficial thrombophlebitis affects veins just under the skin, causing a tender, palpable cord, and generally has a much lower embolic risk, often managed with NSAIDs and compression rather than full anticoagulation unless it is extensive or near the saphenofemoral junction.

Key drugs

ApixabanRivaroxabanEnoxaparinWarfarinDabigatranEdoxabanUnfractionated heparinFondaparinux
Pulmonary embolismSuperficial thrombophlebitisPost-thrombotic syndromeFactor V Leiden thrombophiliaAntiphospholipid syndromeChronic venous insufficiencyPhlegmasia cerulea dolensMay-Thurner syndrome

Sources and further reading

StatPearls (NCBI Bookshelf)MedlinePlusWHO ICD-10: I80.2

Educational content for medical students, prepared by the WhiteCoat Pro editorial team with AI assistance; every page is reviewed by a second AI model for factual errors. It is not medical advice and does not replace the product label, local guidelines or a clinician.