Synopsis
Apply the UK adult DVT probability pathway safely, interpret D-dimer conditionally, and recognise populations needing separate assessment.
- Treat shock, suspected pulmonary embolism, or a rapidly cyanotic painful swollen limb as an emergency; a Wells calculation must not delay resuscitation or specialist escalation.
- In a non-pregnant adult, complete every two-level Wells item: 2 or more is likely DVT and 1 or less is unlikely. Do not apply this generic Wells/D-dimer rule in pregnancy; use an obstetric objective-imaging pathway.
- For unlikely DVT, obtain a D-dimer result within 4 hours: a negative result closes that branch, while a positive result requires a proximal ultrasound result within 4 hours or interim anticoagulation and a result within 24 hours. For likely DVT, seek a proximal ultrasound result within 4 hours; if unavailable, take D-dimer, start interim anticoagulation and obtain the result within 24 hours. After a negative proximal scan, negative D-dimer closes the likely branch, whereas positive D-dimer requires stopping interim treatment and repeat proximal ultrasound in 6–8 days.
Key red flags
Sudden dyspnoea, pleuritic chest pain, haemoptysis, syncope or hypotension suggests pulmonary embolism and needs its own urgent pathway.
A rapidly swollen blue or pale painful leg, sensory loss, weakness or absent arterial signals suggests phlegmasia or threatened limb viability.
Active major bleeding or a recent high-risk intracranial event may contraindicate interim anticoagulation and requires urgent senior planning.
A completed two-level Wells score of 2 or more is likely DVT and prioritises proximal ultrasound before D-dimer when four-hour imaging is available.
Breathlessness, pleuritic pain, haemoptysis, tachycardia, syncope or hypotension demands simultaneous assessment for pulmonary embolism rather than a leg-only pathway.
Rapid progression, cyanosis, severe pain, tense swelling, sensory change or weak arterial signals can indicate phlegmasia and requires emergency vascular assessment.
Reasoning priorities
Set pre-test probability and select the diagnostic sequence.
Two or more is likely and one or less is unlikely; document each positive item and why an alternative diagnosis is or is not equally likely.
Contribute to exclusion within a validated branch: first-line in unlikely DVT and after negative proximal ultrasound in likely DVT.
A negative result closes the unlikely-DVT branch and, with a negative proximal scan, the likely-DVT branch; it is not a stand-alone rule-out for likely DVT. A positive result is nonspecific and advances the defined imaging pathway. Consider an age-adjusted threshold above age 50 using local assay conventions.
Worked reasoning
A non-pregnant adult has Wells score 3 and no proximal ultrasound result can be available within four hours.
- List every Wells item, examine both legs, check for PE or phlegmasia, and record why the score is 3.
- Take D-dimer and baseline full blood count, renal and hepatic function, PT and APTT before treatment when feasible.
- Start an appropriate interim therapeutic anticoagulant without waiting for blood results, unless a contraindication requires an urgent alternative plan.
- Obtain proximal ultrasound with a result within 24 hours and review baseline tests within 24 hours of starting treatment.
- If ultrasound is negative but D-dimer positive, stop interim treatment, arrange repeat proximal ultrasound in 6–8 days, and verify that the appointment and safety-net are documented.