DVT (Deep Vein Thrombosis)
How to investigate and treat DVT (Deep Vein Thrombosis) – for doctors, medical students and medical exams
Types of deep vein thrombosis
- Most deep vein thromboses (DVTs) occur in a leg. These are divided into:
- Above-knee (proximal) DVT if present in the popliteal, superficial femoral (despite the name, still a deep vein), deep femoral, common femoral or external iliac veins
- Below knee (distal) DVT if present in the soleal or peroneal veins
- DVT can also more rarely affect an arm.
- Note thromboses in the saphenous veins or other superficial veins are not DVTs
- ‘Venous thromboembolism’ (VTE) is used to collectively refer to DVT and pulmonary embolism (PE).
Epidemiology of deep vein thrombosis
- Age-standardised incidence of 2 per 1000 person years in adults >45 yrs.
- The incidence in hospital inpatients is much higher, particularly those undergoing surgery. Prior to the widespread use of prophylactic LMWH:
- Rates of asymptomatic DVT in surgical admissions were estimated at >10%
- Approx 4% of medical inpatients developed a symptomatic DVT by day 21
- In the Million Women study, which occurred after the adoption of VTE prophylaxis, rates of VTE were 70-fold higher in patients within 6 weeks of an inpatient operation, than in those not undergoing surgery.
- DVT is important because it can cause pulmonary embolism, which is thought to account for 40,000 hospital deaths each year in the UK.
Prevention of deep vein thrombosis
- All inpatients, who are at high risk of VTE, should have their risk assessed.
- Almost all patients undergoing orthopaedic surgery or significant abdominal surgery (involving an overnight stay in hospital) should receive pharmacological prophylaxis with a low dose of an anticoagulant drug such as a low molecular weight heparin (LMWH), and graduated compression stockings.
- Medical inpatients at high risk should receive pharmacological prophylaxis. The evidence for graduated compression stockings in this population is less strong.
Presentations of DVT
- Unilateral leg pain and/or swelling, usually of insidious onset
- Symptoms may be confined to the calf or the thigh, or affect the whole leg
- The location of symptoms is an unreliable guide to the location of the thrombus
- May be asymptomatic (incidental finding)
- Ask about symptoms of pulmonary embolism
- Bilateral leg swelling is very rarely due to DVT – only if clot has extended around the iliac bifurcation to the other leg, or in the context of pulmonary embolism and right heart failure.
- Rarely presents with fever or sweats
- Examination findings
- Swelling, often tender
- Pitting oedema
- Dilated collateral veins (not varicose veins)
- Evidence of the primary cause:
- Inguinal lymphadenopathy
- Inguinal sinus / discharging abscess from intravenous drug abuse
- Abdominal mass
- Signs of pulmonary embolism
- New atrial fibrillation
- Dullness and reduced breath sounds if pulmonary infarction
Video overview of DVT
Differential diagnosis of deep vein thrombosis
- Ruptured Baker’s cyst (though may co-exist with DVT)
- Asymmetric oedema due to cardiac failure or renal failure
- Muscle haematoma
Scoring of deep vein thrombosis
- The Wells score quantifies the pre-test probability of DVT and guides further investigation:
|Recently bedridden ≥3 days or major surgery in the past 12 weeks||+1|
|Paralysis, paresis or recent plaster immobilization of affected leg||+1|
|Previously documented DVT||+1|
|Calf swelling >3cm more than contralateral leg||+1|
|Swelling of whole leg||+1|
|Localised tenderness along deep venous system||+1|
|Dilated collaterals present (NOT varicose veins)||+1|
|Pitting oedema confined to symptomatic leg||+1|
|An alternative diagnosis is at least as likely||-2|
Initial management of deep vein thrombosis
- After history and examination, calculate the Wells score:
- If <2, perform a D-dimer test – if negative, DVT is excluded. Consider alternative diagnoses.
- If Wells score ≥2, or if the D-dimer is positive, proceed to Doppler and compression ultrasound examination of the venous system. If scanning is delayed, start precautionary anticoagulation whilst it is awaited.
- Proximal DVT requires treatment
- There are no trial data to inform whether below-knee DVT requires treatment, and some centres will not scan below the knee for that reason.
- If diagnosis confirmed, bloods prior to treatment:
- PT and APTT
- Treatment with anticoagulation
- Initial treatment with one of the following:
- Low molecular weight heparin (enoxaparin, dalteparin, or tinzaparin at a therapeutic dose, depending on weight, given sub-cutaneously)
- Apixaban (an oral Xa inhibitor, given at a dose of 10mg twice daily for 7 days, then 5mg twice daily thereafter. It is contraindicated if eGFR<15ml/min.)
- Rivaroxaban (an oral Xa inhibitor, given at a dose of 15mg twice daily for 21 days with food, then 20mg once daily thereafter. It is contraindicated if eGFR<15ml/min)
Further management of deep vein thrombosis
- After initial treatment, anticoagulation can continue with one of the above anticoagulants, or switch to warfarin or dabigatran.
- Warfarin initiation requires frequent INR monitoring, and concurrent LMWH at a therapeutic dose until INR>2 for 24 hours. This is because warfarin also inhibits synthesis of proteins C and S, which have a shorter half life than other vitamin K-dependent clotting factors, and so the initial effect of warfarin is prothrombotic.
- Dabigatran (an oral thrombin inhibitor) is given at a dose of 150mg twice daily, or 110mg twice daily if elderly, if eGFR<50ml/min or receiving concurrent verapamil. It is contraindicated if eGFR<30ml/min.
- Duration of anticoagulation depends on previous history and whether the DVT was provoked by a transient risk factor e.g. surgery.
- Patients with recurrent unprovoked VTE should receive long-term anticoagulation.
- A first episode of provoked VTE requires anticoagulation for at least 3 months, and consider re-scanning for residual thrombus, in which case extend anticoagulation to 6 months.
- Use clinical judgement to assess risk of recurrence in those with first unprovoked VTE or recurrent provoked VTE. In general, most patients do not need anticoagulation beyond 6 months but some will be at high risk of recurrence.
- If anticoagulation is contraindicated (e.g. needs emergency surgery, or platelet count <50×109/L) an inferior vena cava (IVC) filter will reduce the risk of PE, but they trap thrombus in the IVC which can cause venous stasis, promoting further DVT and worsening leg swelling. IVC filters should be removed and anticoagulation initiated as soon as possible.
- Stop any offending drugs e.g. combined oral contraceptive, hormone replacement therapy.
Investigation for underlying causes
- Most risk factors will become apparent in the history, examination and initial testing.
- Consider investigation for underlying malignancy in those over 55yrs with first unprovoked DVT
- Testing for inherited thrombophilias is generally not recommended, as it does not alter management. Furthermore acute thrombus and anticoagulant drugs affect levels of clotting factors so tests are not interpretable.
- In those with recurrent unprovoked DVT or thrombosis in unusual sites (e.g. arm, cerebral sinuses, splanchnic veins) consider testing for antiphospholipid syndrome (Lupus anticoagulant, anti-cardiolipin and anti-β2 glycoprotein 1), myeloproliferative neoplasms (for JAK2 mutations) and paroxysmal nocturnal haemoglobinuria (by flow cytometry).
Complications of deep vein thrombosis
- The major complication is pulmonary embolism, which may be fatal. This is why treatment is needed even if there are no symptoms, urgently.
- A post-thrombotic syndrome is described, including chronic pain, oedema, haemosiderin deposition and varicose veins can develop. Compression stockings are ineffective in preventing it.
- Thrombus can be a nidus for infection, particularly in intravenous drug users, in whom chronic endovascular infection may initially present as occult fever.
Prognosis of deep vein thrombosis
- Isolated DVT generally has a good prognosis, with rates of post-thrombotic syndrome of 5-15% depending on the definition used.
- Recurrent rates depend on the severity of ongoing risk factors.
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