Synopsis
Use venous ultrasound to investigate suspected lower-limb deep-vein thrombosis in non-pregnant adults by matching the examination to clinical probability, distinguishing proximal from whole-leg protocols, interpreting compression and Doppler findings, and linking an adequate result to safe next action.
- Compression ultrasound works because an uninvolved vein should collapse under gentle probe pressure; persistent non-compressibility is the key direct sign of thrombus.
- NICE uses the two-level DVT Wells score first in non-pregnant adults: a likely score of 2 or more leads to proximal leg-vein ultrasound, whereas an unlikely score of 1 or less leads to D-dimer first when promptly available.
- A proximal study assesses the common femoral through popliteal venous segments; a whole-leg examination also interrogates calf veins, so a negative proximal scan is not equivalent to a negative whole-leg scan for isolated calf DVT.
Key red flags
New breathlessness, pleuritic chest pain, haemoptysis, syncope or shock alongside a swollen leg requires an immediate pulmonary embolism assessment.
A markedly painful, cold, cyanotic or neurologically impaired limb needs urgent vascular assessment for phlegmasia or arterial compromise.
A technically limited scan, suspected iliac or caval thrombosis, or symptoms that progress despite a negative proximal study needs senior imaging review and an alternative plan.
The NICE Wells/D-dimer/proximal-ultrasound pathway described here is for non-pregnant adults; suspected DVT during pregnancy or the puerperium requires a pregnancy-specific specialist pathway.
A two-level Wells score of 2 or more places a non-pregnant adult in the likely group and directs proximal leg-vein ultrasound with a result within 4 hours if possible. If it cannot be obtained within 4 hours, obtain D-dimer before interim therapeutic anticoagulation, give interim therapeutic anticoagulation, and obtain ultrasound within 24 hours. If proximal ultrasound is negative and D-dimer positive, stop only interim therapeutic anticoagulation when appropriate and repeat proximal ultrasound in 6–8 days.
A Wells score of 1 or less directs D-dimer first with a result available within 4 hours; if that result cannot be obtained within 4 hours, offer interim therapeutic anticoagulation while awaiting it. A positive result then leads to proximal ultrasound within 4 hours if possible, or interim therapeutic anticoagulation plus ultrasound within 24 hours.
A deep vein remains partly or completely non-compressible, often expands, and may contain hypoechoic or mixed echogenic material with absent or altered colour and spectral flow; the report should specify location and extent.
Oedema, obesity, wounds, dressings, plaster, pain, immobility or deep pelvic anatomy can prevent adequate compression or visualisation; limitations must be stated and managed as unresolved probability rather than falsely negative imaging.
Investigation priorities
Estimate pre-test probability and choose the adult diagnostic sequence rather than ordering ultrasound or D-dimer without context.
Management branches
An adult has unilateral calf swelling after recent surgery; examination finds no PE instability and the two-level Wells score is 3.
- Confirm the Wells items, document leg circumference and alternative diagnoses, and ask specifically about PE symptoms before sending the patient to imaging.
- Request proximal leg-vein ultrasound with a result within 4 hours if possible. If it cannot be obtained within 4 hours, obtain D-dimer before giving interim therapeutic anticoagulation, give interim therapeutic anticoagulation and obtain ultrasound within 24 hours. The sonographer records common femoral, femoral and popliteal compression and states any unexamined segments.