The Wells score for the diagnosis of a DVT.

The Wells score is the most widely used clinical decision tool for the diagnosis of deep vein thrombosis (DVT). This tool risk-stratifies patients into 'low', 'intermediate' and 'high' risk categories for DVT, based on a point system.

A score of less than two indicates low risk, and above two indicates intermediate/high risk.

Criteria	Score
Active cancer (patient receiving treatment for cancer within 6 months or currently receiving palliative treatment).	+1
Paralysis, paresis, or recent plaster or immobilisation of the lower extremeties.	+1
Recently bedridden for 3 days or more, or major surgery within the previous 12 weeks requiring regional anaesthesia.	+1
Localised tenderness along the distribution of the deep venous system.	+1
Entire leg swollen.	+1
Calf swelling at least 3cm larger than that on asymptomatic side (measured 10cm below tibial tuberosity).	+1
Pitting oedema confied to the symptomatic leg.	+1
Collateral superficial veins (non-varicose).	+1
Previously documented deep vein thrombosis.	+1
Alternative diagnosis at least as likely as deep vein thrombosis.	-2

The tool assists the clinician in deciding if the patient requires a duplex ultrasound scan to exclude DVT. In patients with a Wells score of less than two, a whole blood D dimer assay should be performed to exclude a DVT safely.

If the D dimer assay is positive they will require a compression ultrasound. A score above two on the Wells score criteria also means the patient requires a compression ultrasound. If positive, treatment for DVT should be initiated.