Clinical decision rule
Wells DVT Rules
Wells Score for Deep Vein Thrombosis
The Wells score for deep vein thrombosis estimates pre-test probability from ten clinical criteria, nine of which add a point and one of which subtracts two, stratifying patients into low, moderate and high probability groups that carry roughly 5%, 17% and 53% prevalence of DVT.
What the Wells DVT category means
Wells DVT scores run from -2 to 9, where a lower score is better. The bands below are conventional reporting categories, not diagnostic cut-offs.
- Low probability-2–0
Roughly 5% prevalence of DVT in the original three-tier model. A negative D-dimer in this group effectively excludes DVT without imaging.
- Moderate probability1–2
Roughly 17% prevalence in the three-tier model. D-dimer and ultrasound are both commonly used.
- High probability3–9
Roughly 53% prevalence in the three-tier model. Proceed to ultrasound; D-dimer is not sufficient to exclude DVT in this group.
Published criteria and reliability
The published cut-offs that define this instrument, and the measured agreement between observers using it. Each is reported with the population it was derived in.
| Type | Value | Subscale | Population | Follow-up | Source |
|---|---|---|---|---|---|
| Criterion | ≤ 0 — low probability, approximately 5% prevalence | — | Outpatients with suspected DVT | — | Wells PS 1997 |
| Criterion | 1–2 — moderate probability, approximately 17% prevalence | — | Outpatients with suspected DVT | — | Wells PS 1997 |
| Criterion | ≥ 3 — high probability, approximately 53% prevalence | — | Outpatients with suspected DVT | — | Wells PS 1997 |
| Criterion | ≥ 2 — "DVT likely" in the simplified two-tier model | — | Outpatients with suspected DVT | — | Wells PS 2003 |
| Criterion | A negative D-dimer with an "unlikely" Wells score safely excludes DVT without imaging | — | Outpatients, management study | — | Wells PS 2003 |
Criterion is a published cut-off, definition or performance figure belonging to a classification or decision rule — it is not a change score and should not be read as one.
How the score is calculated
Stated in full so the calculation can be independently checked, and reproduced by hand if needed.
Nine clinical criteria each score one point: active cancer, paralysis or recent immobilisation of the lower extremity, recent bed rest of three days or more or major surgery within twelve weeks, localised tenderness along the deep venous system, whole-leg swelling, calf swelling at least 3 cm greater than the asymptomatic side, pitting oedema confined to the symptomatic leg, non-varicose collateral superficial veins, and previously documented DVT. One criterion subtracts two points: an alternative diagnosis at least as likely as DVT. The total ranges from −2 to 9. In the three-tier model, 0 or less is low probability, 1 to 2 is moderate and 3 or more is high. In the simplified two-tier model, 2 or more means DVT is likely and 1 or less means it is unlikely.
Instrument profile
- Developer
- Philip S. Wells and colleagues
- Institution
- Ottawa Hospital Research Institute, Canada
- First published
- 1997
- Items
- 10
- Response format
- Ten criteria, nine scoring +1 and one scoring −2
- Score range
- -2 to 9
- Direction
- Lower score = better
- Completion time
- About 2 minutes
- Age range
- Adults
- Regions
- General Health
- Conditions
- Deep vein thrombosis, Venous thromboembolism, Leg swelling, Post-operative DVT
- Procedures
- Total knee arthroplasty, Total hip arthroplasty, Lower limb fracture fixation
- Validity
- Validated extensively in outpatient populations and embedded in most national DVT pathways, where it is used with D-dimer to decide who requires ultrasound.
- Reliability
- Performance degrades in hospital inpatients, in pregnancy, in intravenous drug users, and in patients with previous DVT, where the "alternative diagnosis" criterion in particular becomes difficult to apply consistently. Interobserver agreement on that criterion is the weakest part of the score.
When to use the Wells DVT
Well suited to
- Outpatients presenting with a symptomatic, swollen or painful leg where DVT is being considered.
- Deciding whether D-dimer alone can safely exclude DVT or whether ultrasound is needed.
- Post-operative orthopaedic patients presenting with calf symptoms, bearing in mind the score performs less well in inpatients.
Limitations and poor fits
- Suspected pulmonary embolism, which has its own separate Wells score with different criteria.
- Pregnancy, where DVT pathways use pregnancy-specific rules.
- As a reason to withhold imaging when clinical suspicion is high regardless of the score.
- Upper limb DVT, which was not part of the derivation population.
Wells DVT compared with other instruments
Instruments measuring a related construct, with the practical difference between them.
| Instrument | Items | Range | What it adds |
|---|---|---|---|
| Caprini | 37 | 0–84 | The Caprini Risk Assessment Model estimates the risk of venous thromboembolism in a surgical patient by adding risk factors weighted 1, 2, 3 or 5 points — with elective lower limb arthroplasty, a hip, pelvis or leg fracture, stroke and acute spinal cord injury each worth 5 — to give a total that hospital protocols then map to a prophylaxis level. |
| CCI | 17 | 0–37 | The Charlson Comorbidity Index is a weighted checklist of 16 comorbid conditions that produces a comorbidity score of 0 to 33, to which up to 4 points are added for age, and which estimates 10-year survival at roughly 98% for a total of 0, 90% for 2, 53% for 4 and 21% for 5. |
Copyright and permitted use
Published openly because it is the question every clinician and researcher asks before using an instrument, and almost nobody answers it.
A published clinical prediction rule. The criteria and point values are freely reproducible and no licence is required.
References
- Wells PS, Anderson DR, Bormanis J, et al.. Value of assessment of pretest probability of deep-vein thrombosis in clinical management. The Lancet. 1997.PMID 9428249
- Wells PS, Anderson DR, Rodger M, et al.. Evaluation of D-dimer in the diagnosis of suspected deep-vein thrombosis. New England Journal of Medicine. 2003.PMID 14507948
Editorial status
This page has not yet been signed off by a named clinical reviewer. The scoring logic is stated in full above so it can be independently verified, and every threshold is traceable to its source. See our editorial methodology.