Deep Venous Thrombosis (DVT) - Assessment

See Clinical scoring systems for DVT - Wells criteria

See Management of DVT

Go directly to the Diagnostic algorithm 

DVT = deep vein thrombosis
U/S = Doppler/Duplex leg ultrasound


  • Any DVT has a chance of embolising and the risk increases the more proximal it extends
  • Clinical findings are not usually not sufficient to diagnose or exclude DVT (ultrasound is the best initial investigation)
  • Patients with an extensive superficial thrombosis within 10cm of the saphenofemoral junction should be considered equally at risk of DVT
  • The annual risk of major bleeding from anti-coagulation varies from 0-4% depending on co-morbidities (the riskiest period is in the first month of treatment)
  • The critical step in assessment is to estimate the clinical likelihood of DVT (see Clinical scoring systems for DVT)
  • In high risk or moderately symptomatic patients, anti-coagulate prior to imaging (if no contraindications)
  • A swollen, white leg may be due to complete and extensive venous obstruction and is a surgical emergency (see Phlegmasia Dolens)


See the Diagnostic algorithm  

Clinical probability testing

  • This is the critical step prior to further testing
  • The pre-test probability markedly influences the interpretation of subsequent ultrasound testing
  • It is prudent to obtain a haematology opinion prior to discharging a high risk patient in which the diagnosis of PE has not been made

 (see Clinical scoring systems for PE)


  • Only has sufficient NPV in non-high clinical probability of DVT (a negative d-dimer result CANNOT rule out DVT in high clinical probability and should not be performed)
  • D-dimer > 0.5mg/L mandates further imaging

Leg Ultrasound

  • A patient with a non-high clinical probability and a normal U/S excludes DVT
  • Not sensitive enough to exclude DVT in high risk patients 
  • May be difficult in distinguishing previous old thrombus from acute thrombus
  • Can used serially in high risk patients if diagnosis uncertain

CT abdomen/pelvis

  • Should be considered in the following cases:
    • Suspected or confirmed abdominal-pelvic malignancy
    • Bilateral leg swelling
    • High risk patients with normal leg ultrasound


  • Considered the gold standard
  • May be useful in high risk patients with normal leg ultrasound
  • Disadvantages are contrast load, painful, can induce DVT

Risk of Anticoagulation

  • The risk of major bleeding from anti-coagulation varies from 1-4% per year depending on a patients risk profile.

(see Estimating risk of bleeding from anticoagulation)