Criteria

Wells score

  • Active cancer (any treatment within past 6 months): 1 point

  • Calf swelling where affected calf circumference measures >3 cm more than the other calf (measured 10 cm below tibial tuberosity): 1 point

  • Prominent superficial veins (nonvaricose): 1 point

  • Pitting edema (confined to symptomatic leg): 1 point

  • Swelling of entire leg: 1 point

  • Localized pain along distribution of deep venous system: 1 point

  • Paralysis, paresis, or recent cast immobilization of lower extremities: 1 point

  • Recent bed rest for >3 days or major surgery requiring regional or general anesthetic within past 12 weeks: 1 point

  • Previous history of DVT or pulmonary embolism: 1 point

  • Alternative diagnosis at least as probable: subtract 2 points.

If the Wells score is 2 or greater, the condition is likely (absolute risk is approximately 40%).[117][118] People with a Wells score of <2 are unlikely to have DVT (probability <15%).[117][118]

Ultrasonography criteria

The radiologist or technician who performs lower-extremity ultrasound first locates the femoral artery and vein in the groin region. The artery and its associated pulsatility can be identified readily; the femoral vein is adjacent. Compression of the femoral vein using the ultrasound probe is easy. Inability to compress the vein indicates the presence of a clot, but provides no information on the age of the clot; further investigation with duplex or color flow Doppler is needed.[149]​ Criteria that suggest acuity of thrombosis have not been well validated, and comparison with previous imaging is the most reliable method to exclude new from prior thrombosis.​

All of the deep veins in the leg must be identified and compressed in a deliberate and systematic fashion (including the deep veins of the calf if whole-leg ultrasound is chosen). There must be a careful search for a duplicated femoral vein and a duplicated popliteal vein.

Secondary criteria include a larger vein diameter on the affected side, and absent or scant echoes within the clot. In acute DVT, the vein is noncompressible and dilated. In subacute DVT, the vein is noncompressible and marginally dilated or of normal size. In chronic DVT, the affected vein is noncompressible and small. Acute DVT is frequently easy to determine on the ultrasound, but where the vein is of normal size or the vein is partially compressible or partially noncompressible, it is more difficult to determine the age of the DVT. In these cases, the DVT is referred to as age-indeterminate.

Compression ultrasound is used to assess the presence of DVT in the deep veins of the upper extremity.[120]​ Compression cannot be performed on the intrathoracic veins (subclavian and innominate veins and superior vena cava). The presence of a DVT in these centrally located veins of the chest is suggested by the absence of flow on color flow Doppler and the absence of respiratory variations on pulse-wave Doppler in a more distal vein.[150] The Wells score does not apply to upper-extremity DVT; however, there is one prospective management study of a risk assessment model for suspected upper-extremity DVT.[151]

Although fewer studies are available, guidelines favor ultrasound as the preferred imaging modality for suspected DVT in the upper extremity. Principles of study interpretation are similar to that above, though the intrathoracic deep veins may not be amenable to compression.[27]

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