Investigations

• Blood count: check platelets ^d
• Clotting: to provide baseline measurements and to exclude problems pre-anticoagulation ^d
• Factor V Leiden, protein C, S, antithrombin, plasminogen, antiphospholipid antibodies if indicated ^d  
  (a family history of thrombophilia and a first thromboembolic event aged < 41) c
  
  
• Consider a d-dimer ^a  in clinically low-risk patients ^a  

• Ultrasound scan  ^a  of the common femoral vein and popliteal vein to the trification. 
  Positive if any vein not fully compressible.

  Using the clinical prediction rule ranking  ^a, read the ultrasound result as follows: 

High risk for DVT  ^a

• Positive scan: DVT
• Negative scan: Venous thromboembolism remains so likely that a venogram is needed.
  • If the venogram is positive: DVT
  • If the venogram is negative: no DVT

Moderate risk for DVT  ^a

• Positive scan: DVT
• Negative scan: Repeat the scan in one week and withhold anticoagulation.
  • If it is positive: DVT
  • If it is negative: no DVT

Low risk for DVT ^a

• Positive scan: Venous thromboembolism remains so unlikely that a venogram is needed.
  • If the venogram is positive: DVT
  • If the venogram is negative: no DVT
• Negative scan: no DVT

Remember 

• Ultrasound scans can diagnose recurrent DVT in patients with a recent deep vein thrombosis. ^a 
  Positive if veins non-compressible or > 2mm increase in clot diameter from last measurement.
• There is little benefit in scanning asymptomatic high-risk patients (e.g. following orthopaedic surgery).  ^a  

Alternatives include:

• Impedance plethysmography. ^a  
  This is less good than ultrasonography. ^a  

Using the clinical prediction rule ranking ^a read the IPG result as follows: 

High risk for DVT  ^a

• Positive scan: DVT
• Negative scan: Venous thromboembolism remains so likely that a venogram is needed.
  • If the venogram is positive: DVT
  • If the venogram is negative: no DVT

Moderate risk for DVT ^a

• Positive scan: DVT
• Negative scan: Repeat the scan in one week and withhold anticoagulation.
  • If it is positive: DVT
  • If it is negative: no DVT

Low risk for DVT ^a

• Positive scan: Venous thromboembolism remains so unlikely that a venogram is needed.
  • If the venogram is positive: DVT
  • If the venogram is negative: no DVT
• Negative scan: no DVT

Combining with a whole blood agglutination d-dimer test makes IPG better at diagnosing and excluding DVT ^a  

Remember

• Impedance plethysmography can diagnose recurrent DVT in patients with a recent deep vein thrombosis. ^c
• There is little benefit in scanning asymptomatic high-risk patients (e.g. following orthopaedic surgery) ^a  
  
  

• venography: ^a the reference standard
  • It can be safely performed in pregnant women if necessary. ^b  

   

• MRI ^b  from inferior vena cava to popliteal veins. 
  Positive if central signal void with hyperintense signal or no flow in vessel (with or without intraluminal thrombus)

I-125 fibrinogen leg scanning - it cannot safely diagnose or exclude DVT ^c