Deep Vein Thrombosis
Deep Vein Thrombosis (DVT) is a thrombus that forms in one of the deep veins of the body, usually the legs. Thromboses of the deep veins in the upper limbs and unusual sites such as mesenteric veins constitute less than 10% of DVT cases. If DVT is not treated there is a risk of Pulmonary Embolism (PE). Pulmonary embolism (symptomatic or asymptomatic) occurs in about 50% of patients with proximal (popliteal and above) DVT and in about 5% of those with distal DVT. (eTG - Treatment of Deep Vein Thrombosis and PE, accessed 3 December 2013)
The single most powerful risk factor is a prior history of DVT. This is seen in 25% of patients.
Anything that slows the flow of blood through the deep veins can cause a DVT.
Examples of immobility include: hospitalisation (>3 days), major surgery in previous 4 weeks, hip or knee replacement surgery, fractures of hip or lower limb, major trauma, spinal cord injury, long haul flights or car journeys (>8 hours), obesity and advancing age.
Medical conditions that predispose to thrombus include:
Cancer and other medical conditions - SLE, Crohns, Rheumatoid arthritis, Glomerulonephritis, Sepsis
Inherited or acquired blood clotting disorders - Factor V Leiden, Prothrombin gene mutations, Protein C, S or Antithrombin III deficiency, Antiphospholipid antibodies
Medications which predispose to thrombosis include:
Oral Contraceptive Pill /Hormone Replacement Therapy
Idiopathic - In 25% no clinical cause can be ascertained.
Swelling, tenderness and warmth in the affected limb.
Up to 50% show no signs.
Other conditions present with similar symptoms to DVTs including muscle strain, phlebitis, cellulitis, dermatitis or ruptured Bakers cyst.
Assessment and diagnosis
Clinical diagnosis is unreliable. Among adults in primary care settings who have signs and/or symptoms of DVT, only 29% had USS proven DVT.
To better evaluate the clinical probability of DVT, validated scoring systems have been developed. One of these is the modified WELLS score which categorises patients as likely or unlikely to have a DVT.
If the pre-test probability is LOW (DVT unlikely) then a D-dimer test should be performed. If negative, a DVT can be reliably excluded. If positive, further imaging is required.
If the pre-test probability is HIGH (DVT likely) then imaging should be performed. A normal scan does not exclude DVT so a D-dimer should be performed after. If this is negative, then a DVT can be excluded. If it is positive, imaging should be repeated within 1 week. This is because an isolated distal DVT that may have been missed initially may extend into proximal veins and be detected on repeat scanning.
In patients with unexplained swelling of the entire leg and a negative scan, the possibility of pelvic vein thrombosis should be considered in which case CT/MRI or venography may be indicated.
Compression Ultrasonography (CUS) is the method of choice to evaluate lower and upper limbs for DVT. Other methods include Venography, CT and MRI.
Blood tests for a hypercoagulable state are required if there is no obvious cause - FBC, Activated protein C resistance, Antithrombin III levels, Antiphospholipid antibodies, Lupus anticoagulant, Protein C and Protein S.
In recent years clinical practice has shifted to favour using NOAC over LMWH for treatment of DVT. Although there has been some debate over the value of treating isolated distal deep vein thrombosis (IDDVT), as opposed to serial imaging in 2 weeks, most recent advice is to commence anticoagulation if there are no contraindications. Cited benefits include prevention of PE, proximal extension and post-thrombotic syndrome, as well as relief of symptoms.
- NPS MedicineWise recommendations
- A discussion of the benefits and risks of treating IDDVT
- NOAC for Peripheral DVT - Presentation by Tim Brighton, Haematologist, Prince of Wales Hospital at ECI Leadership Forum 1 April 2016
General approach to treatment of DVT using NOAC:
- inclusion criteria
- objectively proven DVT
- no symptoms of PE
- no contraindications to anticoagulation
- exclusion criteria
- cancer-associated thrombosis
- prosthetic heart valves
- high risk bleeding or bleeding disorder
- severe kidney or liver disease
- certain medications including antifungals, anti-retroviral protease inhibitors, anticonvulsants, macrolide antibiotics
- expected poor compliance
- prior to commencement
- send baseline FBC, EUC, LFTs, coagulation studies (APTT, PT, Fibrinogen)
- measure weight and calculate GFR
- review medications (avoid aspirin and NSAIDS, certain other medications)
- treatment regimen
- commence at 15 mg po bd
- follow up with GP in the first 3 weeks
- after 3 weeks, continue at 20 mg po daily
- please see this link for more information on NOACs for dosing of other NOACs and adjustment for renal impairment.
Knee length graded compression stockings are strongly recommended to prevent post-thrombotic syndrome (PTS). PTS occurs in 60% of pateints following DVT. It is characterised by pain, swelling and the possible development of pathological changes of venous hypertension, including leg ulceration. Graduated compression stockings reduce the incident and severity of the post-thrombotic syndrome, and are indicated in most cases of DVT. Studies show a number needed to treat (NNT) of 4.3 to prevent 1 PTS. They should be worn for up to 18 months and patients should be encouraged to mobilise ear,ly as this results in decreased pain and swelling and does not increase the risk of PE.
Advice to patients
Return to ED if they develop chest pain, haemoptysis, SOB or syncope.
Provide patient with the DVT Patient Factsheet.
Further References and Resources
ECI Patient Factsheet - DVT
CEC Patient Factsheet - Preventing blood clots
Australian Family Physician - summary paper with a diagnostic algorithm
Medscape - summary
Updated guidelines on therapy and prevention of thrombosis see page 16S
NHMRC Guidelines on VTE Prophylaxis.