Assessing Suspected Venous Thromboembolism
Published October 11, 2026 · Last updated October 11, 2026
How the Wells score for pulmonary embolism, the Wells score for deep vein thrombosis, and the PERC rule estimate pre-test probability of venous thromboembolism and guide D-dimer and imaging decisions.
Suspected venous thromboembolism — pulmonary embolism (PE) and deep vein thrombosis (DVT) — is common in emergency and acute settings, and the clinical question is usually about pre-test probability: how likely is VTE, and which patients can avoid imaging. The library contains three tools for that question: the Wells score for PE, the Wells score for DVT, and the PERC rule.
This guide describes what each tool estimates and how they fit into a diagnostic pathway.
PE or DVT: two presentations, two Wells scores
The Wells score exists in a PE version and a DVT version. Both are clinical models that categorise a patient's probability of the corresponding diagnosis from history and examination, but the items and their weights differ between the two, so the PE score should not be applied to a suspected DVT (or the reverse).
The Wells score for PE
The Wells PE score estimates the pre-test probability of pulmonary embolism to guide D-dimer testing and imaging decisions. It was derived as a simple clinical model to categorise probability and later evaluated in management studies in which D-dimer was used to exclude PE without imaging in low-probability patients.
The Wells score for DVT
The Wells DVT score estimates the pre-test probability of deep vein thrombosis to guide D-dimer testing and compression ultrasound. It was derived to make clinical assessment of DVT more accurate and was subsequently tested in management studies of D-dimer use.
The PERC rule: ruling out PE without testing
The Pulmonary Embolism Rule-out Criteria (PERC) is used when a clinician's gestalt pre-test probability is already low. If all criteria are met, PE can be considered ruled out without D-dimer or imaging; if any criterion is present, the rule does not apply. PERC is therefore layered on top of, rather than a substitute for, a probability assessment.
Limits and sensible use
Each tool was derived and tested in a particular population, and none replaces clinical judgement. A probability that appears low in a patient who is deteriorating, pregnant, or has an unreliable history should not be allowed to override that assessment. For that reason this guide links only the three VTE tools in the library rather than padding the list with unrelated calculators.
Calculators in this guide
Related guides
References
- Wells PS, et al. Derivation of a simple clinical model to categorize patients probability of pulmonary embolism: increasing the models utility with the SimpliRED D-dimer. Thromb Haemost. 2000;83(3):416-420.
- Wells PS, et al. Excluding pulmonary embolism at the bedside without diagnostic imaging: management of patients with suspected pulmonary embolism presenting to the emergency department by using a simple clinical model and D-dimer. Ann Intern Med. 2001;135(2):98-107.
- Wells PS, et al. Evaluation of D-dimer in the diagnosis of suspected deep-vein thrombosis. N Engl J Med. 2003;349(13):1227-1235.
- Wells PS, et al. Accuracy of clinical assessment of deep-vein thrombosis. Lancet. 1995;345(8960):1326-1330.
- Kline JA, et al. Clinical criteria to prevent unnecessary diagnostic testing in emergency department patients with suspected pulmonary embolism. J Thromb Haemost. 2004;2(8):1247-1255.
- Kline JA, et al. Impact of a rapid rule-out protocol for pulmonary embolism on the rate of screening, missed cases, and pulmonary vascular imaging in an urban US emergency department. Ann Emerg Med. 2004;44(5):490-502.