creation date: 2026-06-22 13:47
tags: Pathologies
Deep Vein Thrombosis
Background
Definitions
Deep vein thrombosis (DVT) is an obstructive disease causing impairment of venous return.
Most DVT involves the lower limb venous system but can occur in the arms, mesenteric veins, and cerebral veins. A subtype of upper extremity DVT is effort thrombosis (Paget-Schroetter syndrome).
Etiology & Risk Factors
The risk factors for DVT are summarized by the Virchow triad: hypercoagulability, venous stasis, and endothelial injury.
Risk factors include acquired factors:
- Previous history of DVT
- Active malignancy
- Surgery
- Trauma
- Immobilization (including hospitalization)
- Older age (≥65)
- Pregnancy (RR 4)
- Chronic inflammatory bowel disease
- Cardiovascular disease (eg. heart failure, ASCVD)
- Obesity
- Smoking
- Drugs (OCPs, HRT, tamoxifen, cancer therapy)
- Antiphospholipid antibodies
- Kidney disease
- Hematologic conditions (eg. HIT, hyperviscosity)
Inherited hypercoagulable states include:
- Factor V Leiden mutation
- Protrombin gene mutation
- Protein S or C deficiency
- Antithrombin deficiency
Anatomic factors can increase the risk of DVT:
- Varicose veins
- Paget-Schroetter syndrome (effort thrombosis) – usually due to underlying compressive anomaly at thoracic outlet
- May-Thurner syndrome – compression of left common iliac vein between overlying right common iliac artery and underlying vertebral body
- Inferior vena cava abnormalities
Other cause includes abnormal clotting factors and chemokines resulting in thrombotic event. These are not explained by genetics.
Pathogenesis
Thrombosis is a protective mechanism for prevention of blood loss and patching up of damaged blood vessels. Fibrinolysis counters thrombosis and maintains an equilibrium, preventing thrombi from growing excessively.
When risk factors for thrombus are present, specifically damage to the vessels, blood flow turbulence and/or stasis, and hypercoagulability, thrombus propagation occurs.
In the lower extremities, DVT occurs most frequently in low-flow sites such as the soleal sinuses, behind venous valve pockets. In the upper extremities, repetitive or high exertional actions can cause endothelial damage to the subclavian vein which can cause effort thrombosis.
Formation of the clot blocks venous return leading to the manifestations.
Clinical Presentation
Signs & Symptoms
Classically, DVT presents as unilateral:
- Swelling or edema
- Pain and tenderness along course of involved major veins
- Warmth
- Erythema
- Dilated superficial veins
For pregnant and postpartum patients, three important distinctions are notable:
- Predominantly left-sided (90-97%)
- Higher rates of pelvic vein thrombosis
- Overlapping symptoms with pregnancy (apply higher level of suspicion)
History & Physical Exam
History should assess risk factors for DVT.
Physical should include examination of the limb in comparison to the unaffected limb. Additionally, a pulmonary exam should be done for PE findings.
Diagnosis
Criteria
Diagnosis of DVT is made by compressive ultrasound with doppler. Decision to undergo US can be made using risk stratification criteria (see work-up).
Ultrasound Findings
Positive findings include:
- Demonstration of noncompressibility of the imaged vein (note, distal veins are less compressible)
- Apparent thrombus “free-floating”, poorly adherent to the adjacent vessel wall
Negative if veins demonstrate full compressibility.
Nondiagnostic, indeterminant studies occur if:
- Difficulty visualizing the deep veins due to body habitus or symptoms
- Atypical abnormalities/appearance of the deep veins with uncertain significance
- Uncertainty regarding residual thrombosis from prior DVT or acute
Work-up
Laboratory studies
Routine labs may be ordered but are not useful for diagnosis. They may aid in narrowing the differential diagnosis or provide clues on underlying cause if DVT is diagnosed.
Determine pretest probability
Can be done using clinical gestalt or using a validated score such as Wells or modified Wells score. The Wells score stratifies risk into three categories seen in next step. Points are given as per MDCalc:
- Malignancy with treatment in last 6 months or palliative (+1)
- Bedridden recently for >3 days or major surgery within 12 weeks (+1)
- Paralysis, paresis, or recent plaster immobilization of lower extremity (+1)
- Previous DVT (+1)
- Calf swelling >3 cm compared to other leg, 10 cm below tibial tuberosity (+1)
- Entire leg swollen (+1)
- Collateral (nonvaricose) superficial veins present (+1)
- Localized tenderness along deep venous system (+1)
- Pitting edema, confined to symptomatic leg (+1)
- Alternative diagnosis to DVT as or more likely (-2)
Risk is as follows:
- ≤0: low probability (3% prevalence)
- 1-2: moderate probability (17% prevalence)
- 3-8: high probability (50-75% prevalence)
Note, for pregnant patients, gestalt is preferred over Wells score as they are not validated for pregnancy use and due to the distinctions described above.
D-dimer
A high sensitivity d-dimer should be obtained for patients with ≤2 points from the Wells score. It should not be done if it is expected to be positive from another condition (move to compression ultrasound).
- D-dimers <500 ng/mL can exclude DVT
- D-dimers ≥500 ng/mL indicates compression ultrasound
Note that d-dimer levels may rise with age, resulting in a reduced specificity for patients >50 years of age. Consider using an adjusted d-dimer.
Compression ultrasound
For patients with a positive d-dimer, where d-dimer would be elevated regardless, or with a Wells score ≥3, a compressive ultrasound with doppler is indicated for diagnosis.
In all pregnant patients suspected of having a DVT, consider whole-leg CUS (traditional approach).
Differential
Other causes of leg pain include:
- Muscle strain, tear, or twisting injury
- Leg swelling in a paralyzed limb
- Lymphangitis or lymphatic obstruction
- Venous insufficiency
- Popliteal (Baker’s) cyst
- Cellulitis
- Knee abnormality
Red Flags / Complications
Complications include:
- Pulmonary embolism
- Post-thrombotic syndrome (chronic venous insufficiency)
- Paradoxical embolization
Management
General Measures
Anticoagulation is the mainstay management for DVT. Generally, anticoagulation is indicated for proximal DVT and some distal DVT.
Anticoagulation is not used if there is an absolute contraindication present. Additionally, further evaluation for bleeding risk is performed:
- Intracranial or spinal t umours
- Recurrent GI bleeds
- Large AAA with concurrent severe hypertension
- Stable aortic dissection
- Recent, planned, or emergent low-bleeding-risk procedure
- Older age or frequent falls
- Non-severe thrombocytopenia
- History of bleeding
- Active cancer
- Acute ischemic stroke
- Comorbidities
- Anemia
- Excess alcohol use
Ambulation is encouraged as soon as feasible. The risk of PE during aggressive forms of exercise is unknown and thus gradually increasing exercise training as tolerated is recommended.
Graduated compression stockings are not routinely used as their cost does not necessarily justify the uncertain benefit. Consider if symptoms are more severe as GCS are rarely harmful.
Proximal DVT Treatment
For patients without a contraindication or unacceptably high risk for bleeding, anticoagulant therapy is started immediately. Therapy consist of:
- Initial phase for 0-10 days following diagnosis (UFH, LMWH, fondaparinux)
- Treatment phase of anticoagulant therapy for 3-6 months (DOACs)
Outpatient therapy is generally sufficient unless disease is extensive, intervention is being considered, or severe risk factors are present.
For patients with an absolute contraindication to anticoagulation, an IVC filter may be considered.
Distal DVT Treatment
The risk of PE is lower for distal DVTs (distal to popliteal vein). As such, the acceptable bleeding risk of anticoagulation is lower than for proximal DVTs. For many patients, isolated distal DV T resolve spontaneously without anticoagulation (up to 40%).
Risk factors for of proximal extension are:
- Presence of symptoms
- Thrombus close to popliteal vein (within 1-2 cm)
- Unprovoked DVT
- D-dimer elevated
- Extensive thrombosis involving multiple veins
- Persistent risk factors
- Prior DVT/PE
- Inpatient status
- Severe COVID-19 disease
In cases of high extension risk and low bleeding risk, initiate anticoagulation.
In cases of high extension risk and high bleeding risk, consider serial weekly compressive ultrasound for two weeks.
In cases of low extension and bleeding risk, patient preference should be considered.