• Clinical science

Deep vein thrombosis (Phlebothrombosis)


Deep vein thrombosis (DVT) is the formation of a blood clot in a deep vein of the legs, thigh, or pelvis. Thrombosis is most often seen in individuals with a history of immobilization, obesity, malignancy, or hereditary thrombophilia. Vascular endothelial damage, venous stasis, and hypercoagulability, collectively referred to as the Virchow triad, are the main factors contributing to the development of DVT. Symptoms usually occur unilaterally and include swelling, tenderness, and redness or discoloration. Pulmonary embolism (PE), a severe complication of DVT, should be suspected in patients with dizziness, dyspnea, and fever. The diagnostic test of choice for DVT is compression ultrasound. In most cases, a negative D-dimer test allows thrombosis or PE to be ruled out, but a positive test is nonspecific. Initial acute treatment of DVT consists of anticoagulation with heparin and, if the thrombus is large or unresponsive to anticoagulation, may also include thrombolysis or thrombectomy. Secondary prophylaxis is achieved with oral warfarin or direct factor Xa inhibitors and supportive measures such as regular exercise and compression stockings.


Risk factors for deep vein thrombosis

To remember the risk factors of deep vein thrombosis, think “THROMBOSIS”: Travel, Hypercoagulable/HRT, Recreational drugs, Old (> 60), Malignancy, Blood disorders, Obesity/Obstetrics, Surgery/Smoking, Immobilization, Sickness (CHF/MI, IBD, nephrotic syndrome, vasculitis)!



The Virchow triad

The Virchow triad refers to the three main pathophysiological components of thrombus formation.

  1. Hypercoagulability: increased platelet adhesion, thrombophilia (e.g., Factor V Leiden mutation), use of oral contraceptives, pregnancy
  2. Endothelial damage: inflammatory or traumatic vessel injuries can lead to activation of clotting factors through contact with exposed subendothelial collagen
  3. Venous stasis: varicosis, external pressure on the extremity, immobilization (e.g., hospitalization, bed rest, long flights or bus rides), local application of heat

To remember the three pathophysiological components of thrombus formation, think: “HE'S Virchow”: H-Hypercoaguability, E-Endothelial damage, S-Stasis.


Clinical features


Subtypes and variants

Phlegmasia cerulea dolens

Paget-Schroetter disease (upper extremity DVT)



The diagnostic approach for suspected DVT is determined by the Wells score. Compression ultrasonography and D-dimer levels are the main diagnostic tests.

Wells criteria for deep vein thrombosis

The Wells score for DVT identifies the probability of DVT. A different version of the score may be used to determine the probability of PE (see Wells criteria for PE).

Criteria Score
Medical history Active cancer +1
Previously documented DVT +1
Immobilization Paralysis or recent (cast) immobilization of lower extremity +1
  • Recently bedridden (≥ 3 days) or
  • Major surgery (< 12 weeks)
Clinical symptoms Tenderness localized along the deep venous system +1
Swelling of the entire leg +1
Calf swelling ≥ 3 cm compared to asymptomatic calf +1
Unilateral pitting edema in symptomatic leg +1
Presence of collateral (non-varicose) superficial veins +1
Differential diagnosis Alternative diagnosis at least as likely as DVT -2


  • 2 risk group
    • < 2: DVT unlikely (low risk)
    • ≥ 2: DVT likely (high risk)
  • OR 3 risk group
    • 0: low risk
    • 1–2: moderate risk of DVT
    • ≥ 3: high risk of DVT

Compression ultrasonography with Doppler (test of choice)

  • Description
    • A combination of ultrasonography (to visualize the vein) and Doppler (to assess blood flow abnormalities) in which the examiner applies gentle pressure to normally compressible veins using an ultrasound probe
    • High sensitivity and specificity in the popliteal and femoral veins, but very operator dependent
  • Indications: clinical suspicion of a DVT or pulmonary embolism
  • Findings: noncompressibility of the obstructed vein, visible hyperechoic mass, absent or abnormal flow in Doppler imaging

D-dimer testing

  • High sensitivity (∼ 95%), low specificity (∼ 50%)
  • Useful for ruling out DVT (normal D-dimer levels rule out DVT)
  • Elevated D-dimers alone are not proof of DVT.

Further diagnostic tests


Differential diagnoses

Superficial thrombophlebitis

Other differential diagnoses of DVT


The differential diagnoses listed here are not exhaustive.



Additional therapy




We list the most important complications. The selection is not exhaustive.