How the Wells Score for DVT Works (With a Worked Example)
The Wells score for deep vein thrombosis (DVT) rates how likely a leg clot is before any imaging. You add one point for each of nine clinical findings and subtract two points if another diagnosis is at least as likely as DVT. The total sorts the patient into “DVT likely” or “DVT unlikely,” which decides whether you go straight to ultrasound or start with a D-dimer blood test.
This guide lists all ten criteria with their point values, walks through a scored example, explains both the two-tier and three-tier cutoffs, and covers the mistakes that push a patient into the wrong pathway.
The ten criteria
Nine findings each add 1 point. The tenth, an alternative diagnosis, is the only one that subtracts, and it subtracts 2.
| Criterion | Points |
|---|---|
| Active cancer (treatment 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 more than 3 cm vs the other leg | +1 |
| Pitting edema confined to the symptomatic leg | +1 |
| Collateral (non-varicose) superficial veins | +1 |
| Previously documented DVT | +1 |
| Alternative diagnosis at least as likely as DVT | -2 |
The calf measurement is taken 10 cm below the tibial tuberosity, and the 3 cm difference is what earns the point, not just “looks bigger.” The alternative-diagnosis item is the one that trips people up, so it gets its own section below.
Why one item subtracts 2 points
The alternative-diagnosis criterion is a deliberate brake. If a ruptured Baker’s cyst, cellulitis, or a muscle tear explains the swollen, painful leg at least as well as a clot would, the score drops by 2. That single item can move a patient from “likely” back to “unlikely,” which is the whole point: it stops the score from over-calling DVT when there is a plainer explanation in front of you.
Worked example
A patient with active cancer presents with a swollen, tender leg. On exam: the entire leg is swollen, the calf is 4 cm larger than the other side, and there is localized tenderness along the deep veins. No alternative diagnosis fits better.
| Finding | Points |
|---|---|
| Active cancer | +1 |
| Entire leg swollen | +1 |
| Calf swelling more than 3 cm | +1 |
| Localized tenderness | +1 |
| Alternative diagnosis | 0 |
| Total | 4 |
A total of 4 means DVT likely on the two-tier model and high probability on the three-tier model. The next step is a compression ultrasound, not a D-dimer, because in a “likely” patient a negative D-dimer is not enough to rule out a clot on its own.
Score it yourself
Two-tier vs three-tier cutoffs
There are two ways to read the total, and they answer slightly different questions.
| Model | Bands |
|---|---|
| Two-tier (current, most used) | Score 2 or more = DVT likely; below 2 = DVT unlikely |
| Three-tier (older) | 0 = low; 1 to 2 = moderate; 3 or more = high |
The modern two-tier version pairs directly with the testing pathway. DVT unlikely (score below 2): get a D-dimer; if it is negative, DVT is effectively ruled out and no imaging is needed. DVT likely (score 2 or more): go to compression ultrasound. The score is a pretest probability, so it guides which test comes next, it does not diagnose or exclude a clot by itself.
Common mistakes
Forgetting to subtract for the alternative diagnosis. This is the most common error and it inflates the score. If cellulitis or a Baker’s cyst explains the leg just as well, you subtract 2. Leaving it out can push an “unlikely” patient into an unnecessary ultrasound.
Using a negative D-dimer in a “likely” patient. The D-dimer rules out DVT only in the unlikely group. In a likely patient (score 2 or more), a negative D-dimer does not clear them; they still need imaging.
Confusing it with the Wells score for PE. There are two separate Wells scores, one for DVT and one for pulmonary embolism, with different criteria and cutoffs. This is the DVT version. Do not mix the item lists.
Eyeballing the calf instead of measuring. The point is for a measured difference of more than 3 cm, taken 10 cm below the tibial tuberosity, not a visual impression that one calf looks fuller.
Frequently asked questions
What Wells score means DVT is likely?
On the current two-tier model, a score of 2 or more means DVT is likely and the patient should go to compression ultrasound. A score below 2 means DVT is unlikely, and a D-dimer is used to decide whether imaging is needed at all.
What is the lowest possible Wells DVT score?
Negative 2. If the only box that applies is the alternative diagnosis, the score is -2. Any negative or zero total sits firmly in the low-probability, “unlikely” range.
Is the Wells score for DVT the same as the one for PE?
No. They share a name and an author but are different tools with different criteria. The DVT score assesses a leg clot; the PE score assesses a suspected pulmonary embolism. Use the one that matches the clinical question.
Can I diagnose DVT from the Wells score alone?
No. The Wells score is a pretest probability that tells you which test to do next, a D-dimer or an ultrasound. The diagnosis is confirmed or excluded by that testing, not by the score.