Wells Score for DVT
Inputs
| Active cancer | No |
|---|---|
| Paralysis, paresis, or recent leg immobilization | No |
| Recently bedridden or major surgery | No |
| Localized tenderness | No |
| Entire leg swollen | No |
| Calf swelling >3 cm | No |
| Pitting edema (symptomatic leg) | No |
| Collateral superficial veins | No |
| Previously documented DVT | No |
| Alternative diagnosis at least as likely | No |
Wells Score for DVT
Estimate the pretest probability of deep vein thrombosis (DVT) with the modified two-tier Wells score, and see whether the result points toward a D-dimer test or a leg-vein ultrasound.
Inputs
Clinical criteria
Results
Enter a value to see results.
A score of 1 or less places this in the "DVT unlikely" group, with roughly a 6% chance of DVT. The usual next step is a D-dimer test — only a negative D-dimer effectively rules out DVT. This is general information, not a treatment recommendation.
Wells Score for DVT
A deep vein thrombosis (DVT) is a blood clot in one of the deep veins, usually in the leg. It matters because part of the clot can break loose and travel to the lungs, causing a pulmonary embolism. The trouble is that leg pain and swelling are common and have many causes, so doctors need a structured way to judge how likely a clot really is before ordering tests. The Wells score turns ten clinical findings into a single number that sorts patients into "DVT likely" or "DVT unlikely" and points to the right next test.
Why pretest probability matters
No single test is perfect on its own. A D-dimer blood test is very good at ruling out a clot when it is negative, but it is often positive for unrelated reasons, so a positive result proves little. An ultrasound is accurate but uses scanner time and staff. Combining a probability estimate with the right test is what makes the pathway both safe and efficient: low-probability patients can often be cleared with a simple blood test, while higher-probability patients go straight to imaging.
How the Wells score is built
The score adds one point for each of nine clinical criteria and subtracts two points for one:
| Criterion | Points |
|---|---|
| Active cancer (treatment ongoing, within 6 months, or palliative) | +1 |
| Paralysis, paresis, or recent plaster immobilization of the leg | +1 |
| Recently bedridden ≥3 days, or major surgery within 12 weeks | +1 |
| Localized tenderness along the deep venous system | +1 |
| Entire leg swollen | +1 |
| Calf swelling >3 cm vs. the asymptomatic side | +1 |
| Pitting edema confined to the symptomatic leg | +1 |
| Collateral superficial (non-varicose) veins | +1 |
| Previously documented DVT | +1 |
| Alternative diagnosis at least as likely as DVT | −2 |
The total ranges from −2 to +9:
W=∑(present criteria)−2×(alternative diagnosis)For example, an entire swollen leg (+1) with localized tenderness (+1) gives a score of 2. If the clinician judges that cellulitis is at least as likely (−2), the same patient drops to a score of 0.
Reading the result: the two-tier pathway
The modern, modified Wells model uses two bands, and each maps to a specific next step:
- Score ≥ 2 — DVT likely (about a 28% chance of DVT). Proceed to a proximal leg-vein (compression) ultrasound.
- Score < 2 — DVT unlikely (about a 6% chance). Proceed to a D-dimer test. A negative D-dimer effectively excludes DVT; a positive one leads to an ultrasound.
This two-tier split, validated by Wells et al. (2003) and adopted by NICE guideline NG158, is the version most services use because the bands line up directly with the next decision.
The older three-tier model
The original 1997 Wells score had nine criteria (it did not yet include "previously documented DVT") and reported three bands:
- ≤0 points — low probability (~5%)
- 1–2 points — moderate (~17%)
- ≥3 points — high (~53%)
The 2003 modification added the prior-DVT criterion and collapsed the result into the likely/unlikely split. The three-tier model still appears in older material, but the two-tier version is the current standard because it routes patients to a test rather than just labeling their risk.
What the score does and does not do
The Wells score estimates probability to guide testing — it does not diagnose or exclude a clot by itself. A diagnosis of DVT requires imaging, and ruling it out in the "unlikely" group requires a negative D-dimer. The percentages above are population estimates from the validation cohorts, not a prediction for any one person.
The score is validated for adult outpatients with a suspected first lower-extremity DVT. It is not validated in pregnancy, in IV drug users, in suspected recurrent DVT in the same leg, or in upper-extremity DVT; those situations use different pathways. Any decision about D-dimer testing, imaging, or anticoagulation should be made by a qualified clinician.
For related clinical tools, see the QTc Calculator (Corrected QT Interval) and the Blood Pressure Classifier.
Frequently Asked Questions (FAQ)
What is a "DVT likely" Wells score?
A total of 2 points or more is classified as "DVT likely". This group has roughly a 28% chance of having a deep vein thrombosis and is usually sent straight to a proximal leg-vein (compression) ultrasound rather than starting with a blood test. For example, an entire leg swollen (1) plus localized tenderness (1) reaches a score of 2.
What does a low or "unlikely" Wells score mean?
A score of 1 or less is "DVT unlikely", with about a 6% probability of DVT. The score alone does not exclude a clot. In this group a D-dimer blood test is done next, and only a negative D-dimer effectively rules out DVT. A positive D-dimer still leads to an ultrasound.
What is the difference between the two-tier and three-tier Wells score?
The original 1997 Wells score had nine criteria and three tiers — low (≤0), moderate (1–2), and high (≥3) probability. The 2003 modified score added a "previously documented DVT" criterion and collapsed the result into two tiers, likely (≥2) and unlikely (≤1). The two-tier version is now standard because each band maps directly to the next test: ultrasound for "likely", D-dimer for "unlikely".
Why does the alternative-diagnosis item subtract points?
If another explanation for the leg symptoms — such as cellulitis, a Baker’s cyst, or a muscle strain — is at least as likely as DVT, the chance that the symptoms are actually caused by a clot is lower. To reflect that, the item removes 2 points, which can pull the total below the "likely" threshold and route the patient to a D-dimer test instead of straight to ultrasound.
Can the Wells score diagnose or rule out DVT by itself?
No. The Wells score only estimates pretest probability to decide which test comes next — a D-dimer or an ultrasound. A diagnosis of DVT requires imaging (usually ultrasound), and ruling it out requires a negative D-dimer in the "unlikely" group. The score is a triage tool, not a final answer.
Does the Wells score apply during pregnancy?
No. The Wells DVT score is not validated in pregnancy, and dedicated pathways (such as the LEFt rule and ultrasound) are used instead. It also does not apply to suspected recurrent DVT in the same leg, to upper-extremity DVT, or to IV drug users — those situations need different assessment.
Disclaimer
This calculator is for education and general reference; it is an estimate of pretest probability, not a diagnosis. The Wells score guides whether a D-dimer test or an ultrasound is needed — it cannot diagnose or rule out DVT on its own.
It is validated for adult outpatients with a suspected first lower-extremity DVT and not for pregnancy, IV drug use, suspected recurrent DVT in the same leg, or upper-extremity DVT. Decisions about testing, imaging, and anticoagulation must be made by a qualified clinician.