Deep vein thrombosis

Definition/diagnostic criteria Deep vein thrombosis (DVT) is the formation of a thrombus (blood clot) in a deep vein, which partially or completely obstructs blood flow. The thrombus can dislodge and travel in the blood causing pulmonary embolism (PE).

• Provoked DVT is DVT associated with a transient risk factor such (e.g. significant immobility, surgery, trauma, pregnancy or puerperium, combined contraceptive pill).
• Unprovoked DVT is DVT occurring in the absence of a transient risk factor. The person may have no identifiable risk factor or a risk factor that is persistent and not easily correctable (e.g. active cancer or thrombophilia).

Duplex ultrasound is the gold standard for diagnosing DVT

Epidemiology The incidence of DVT is 1-2 individuals per 1,000 each year.

DVT risk factors include age, immobility (e.g., following surgery or long-distance travel), obesity, pregnancy, oral contraceptive use, smoking, and underlying medical conditions such as cancer, inflammatory conditions (e.g. inflammatory bowel disease, vasculitis) and inherited thrombophilias.

Diagnosis
Clinical features:

• Unilateral leg pain and tenderness.
• Swelling of the affected limb (a difference of >3cm in leg circumference measured 10cm below the tibial tuberosity).
• Increased warmth and erythema over the affected area.
• Vein distension.

Investigations Pregnant women and those who have given birth within the past 6 weeks should be referred immediately for same day assessment

For all other people with suspected DVT, use the two-level DVT Wells Score to assess the probability of DVT.

Score 1 point for each of the following:

• Active cancer (treatment ongoing, within the last 6 months, or palliative).
• Paralysis, paresis or recent plaster immobilisation of the legs.
• Recently bedridden for 3 days or more, or major surgery within the past 12 weeks.
• Localised tenderness along the distribution of the deep venous system (e.g. back of the calf).
• Entire leg is swollen.
• Calf swelling by more than 3 cm compared with the asymptomatic leg.
• Pitting oedema confined to the symptomatic leg.
• Collateral superficial veins.
• Previously documented DVT.

Subtract 2 points if an alternative cause is considered at least as likely as DVT.

• For people who are likely to have DVT (Wells score = 2 points or more):
  • Offer a proximal leg vein ultrasound scan with the results available within 4 hours if possible. If results cannot be obtained within 4 hours of being requested, offer:
    • A D-dimer test, then
    • Interim therapeutic anticoagulation (if possible, choose an anticoagulant that can be continued if DVT is confirmed) and 
    • A proximal leg vein ultrasound scan with the results available within 24 hours.
• For people who are unlikely to have DVT (Wells score = 1 point or less):
  • Offer a D-dimer test with the results available within 4 hours. If the results cannot be obtained within 4 hours:
    • Offer interim therapeutic anticoagulation while awaiting the result (if possible, choose an anticoagulant that can be continued if DVT is confirmed).
  • If the D-dimer test is positive, offer a proximal leg vein ultrasound scan with the results available within 4 hours if possible. If the results cannot be obtained within 4 hours:
    • Offer interim therapeutic anticoagulation and a proximal leg vein ultrasound scan with the result available within 24 hours.
  • If the D-dimer test is negative:
    • Stop interim therapeutic anticoagulation.

People with unprovoked DVT should be investigated for undiagnosed cancer or thrombophilia.

Treatment First line is apixaban or rivaroxaban. Alternatives are:

• Low molecular weight heparin (LMWH) for at least 5 days followed by dabigatran or edoxaban, or 
• LMWH concurrently with a vitamin K antagonist for at least 5 days.

Baseline blood tests include full blood count, renal and hepatic function, prothrombin time (PT), and activated partial thromboplastin time (APTT) for people starting interim anticoagulant therapy. Do not wait for results before starting anticoagulation treatment but the results should be reviewed and actioned within 24 hours.

Prognosis Patients should be educated about the risk of recurrence and long-term anticoagulation therapy. Additionally, they should be advised to seek medical attention promptly if they experience any recurrent symptoms or signs of complications, such as pulmonary embolism.