Why estimate the probability first?
Deep vein thrombosis (DVT) is a blood clot in a deep vein, usually in the leg. Its symptoms, pain and swelling, are shared with many other conditions. The Wells score for DVT, published by Philip Wells in 1997 and updated in 2003, estimates the clinical probability so that tests are used efficiently.
The criteria
| Criterion | Points |
|---|---|
| Active cancer | +1 |
| Paralysis, paresis or recent plaster cast of the leg | +1 |
| Bedridden 3 days or more, or major surgery within 12 weeks | +1 |
| Localized tenderness along the deep veins | +1 |
| Entire leg swollen | +1 |
| Calf swelling ≥3 cm compared with the other leg (measured 10 cm below the tibial tuberosity) | +1 |
| Pitting edema in the symptomatic leg | +1 |
| Collateral superficial veins (not varicose) | +1 |
| Previously documented DVT | +1 |
| Alternative diagnosis at least as likely as DVT | −2 |
Worked example
A patient has tenderness along the calf veins and a calf 4 cm larger than the other, with no other criteria: 1 + 1 = 2 points. DVT is “likely”, so a compression ultrasound is recommended.
Reading the score
Two levels (current practice):
- Below 2: DVT unlikely. A negative high-sensitivity D-dimer rules it out. If positive, do an ultrasound.
- 2 or more: DVT likely. Do a compression ultrasound; if negative, a D-dimer or repeat ultrasound in a week may be needed.
Three levels (original study):
| Score | Probability | Prevalence of DVT |
|---|---|---|
| 0 or less | Low | about 5% |
| 1–2 | Moderate | about 17% |
| 3 or more | High | about 53% |
Common alternative diagnoses
Muscle strain or tear, ruptured Baker’s cyst, cellulitis, superficial thrombophlebitis, lymphedema and heart failure can all mimic DVT.
Why it matters
Untreated DVT can lead to pulmonary embolism and to long-term leg pain and swelling (post-thrombotic syndrome). Confirmed DVT is treated with anticoagulants, usually a direct oral anticoagulant, for at least 3 months.
If leg symptoms come with sudden shortness of breath, chest pain or coughing up blood, call 911.
This calculator is for general information and education. It is not medical advice and does not replace the judgment of a doctor, nurse or pharmacist who knows the full clinical picture.