Wells’ criteria for deep vein thrombosis (DVT)

Wells’ criteria for deep vein thrombosis (DVT) is a clinical prediction rule used to estimate the pre-test probability of DVT in patients presenting with symptoms suggestive of venous thromboembolism.

The score supports diagnostic decision-making by stratifying patients into likelihood categories and guiding the appropriate use of D-dimer testing and imaging.

Clinical context and use

Wells’ criteria is used in primary care, emergency departments, and hospital settings when assessing patients with symptoms such as unilateral leg swelling, pain, erythema, or tenderness.

Its primary role is to estimate the probability of DVT before investigation, helping clinicians decide whether DVT can be ruled out with D-dimer testing or whether immediate imaging is required.

The score is most useful in patients with a first presentation of suspected lower-limb DVT and no clear alternative diagnosis.

One point is assigned for each of the following clinical features:

• Active cancer, defined as ongoing treatment, treatment within the previous 6 months, or palliative care

• Paralysis, paresis, or recent plaster immobilisation of the lower limbs

• Recently bedridden for more than 3 days, or major surgery within the previous 12 weeks requiring general or regional anaesthesia

• Localised tenderness along the distribution of the deep venous system

• Entire leg swelling

• Calf swelling of 3 cm or more compared with the asymptomatic leg, measured 10 cm below the tibial tuberosity

• Pitting oedema confined to the symptomatic leg

• Collateral superficial veins that are non-varicose

• Previously documented DVT

Two points are subtracted if an alternative diagnosis is at least as likely as DVT.

The total score is used to estimate the clinical probability of DVT.

In the traditional three-level model:

• 0 points or fewer indicates low probability

• 1–2 points indicates moderate probability

• 3 points or more indicates high probability

In the simplified two-level model, which is commonly used in UK practice:

• 1 point or fewer indicates DVT unlikely

• 2 points or more indicates DVT likely

Local pathways and guidelines should be followed when applying either model.

Wells’ criteria is typically used as the first step in a structured DVT assessment pathway.

In patients classified as DVT unlikely, a negative D-dimer test can often be used to safely exclude DVT without the need for imaging. In patients classified as DVT likely, or with a positive D-dimer, compression ultrasound is usually indicated.

The score helps reduce unnecessary imaging while maintaining patient safety.

Wells’ criteria was developed and validated in outpatient and emergency department populations and has been shown to safely reduce the need for diagnostic imaging when combined with D-dimer testing.

It remains one of the most widely used clinical prediction rules for suspected DVT and is incorporated into many national and international guidelines.

Wells’ criteria does not diagnose DVT and should not be used in isolation.

Its accuracy may be reduced in certain populations, including:

• Hospital inpatients

• Pregnant patients

• Patients with recurrent DVT

• Patients already receiving anticoagulation

Clinical judgement is essential, particularly where symptoms are severe, atypical, or rapidly progressive.

Using Wells’ criteria provides a structured and reproducible approach to assessing suspected DVT. Documenting the score can support clinical reasoning, guide investigation, and aid communication between healthcare professionals.

Clear safety-netting advice should be provided, especially when DVT is considered unlikely but symptoms persist or worsen.