What is the step‑by‑step approach to rule out deep‑vein thrombosis in an adult presenting with leg swelling, pain, tenderness and risk factors such as recent surgery, immobilisation, cancer, prior venous thromboembolism, hormonal therapy, obesity, pregnancy, or long‑haul travel?

Diagnostic Approach to Rule Out Deep Vein Thrombosis

Use the Wells score to stratify pretest probability, then proceed with high-sensitivity D-dimer testing for low-probability patients (score <2) or proceed directly to complete duplex ultrasound for likely-probability patients (score ≥2). 1, 2

Step 1: Calculate Wells Score for Pretest Probability

Apply the Wells clinical prediction rule to every patient before ordering imaging 1:

Wells Score Components (1 point each):

• Active cancer (treatment within 6 months or palliative care) 1
• Paralysis, paresis, or recent plaster immobilization of lower extremities 1
• Recently bedridden ≥3 days or major surgery within 12 weeks 1
• Localized tenderness along deep venous system distribution 1
• Entire leg swollen 1
• Calf swelling ≥3 cm larger than asymptomatic side (measured 10 cm below tibial tuberosity) 1
• Pitting edema confined to symptomatic leg 1
• Collateral superficial veins (nonvaricose) 1
• Previously documented DVT 1
• Alternative diagnosis at least as likely as DVT: subtract 2 points 1

Interpretation:

• Score <2 = DVT unlikely (5% prevalence) 1, 3
• Score ≥2 = DVT likely (17-53% prevalence depending on score) 1, 3

Step 2: Low Pretest Probability (Wells Score <2)

Order high-sensitivity D-dimer first 1, 2:

• If D-dimer negative: DVT is excluded; no further testing needed (99% negative predictive value) 1, 2, 3
• If D-dimer positive: Proceed to complete duplex ultrasound 1, 2

The American College of Chest Physicians recommends D-dimer over immediate ultrasound in low-probability patients because most will have negative D-dimer results, avoiding unnecessary imaging 1. However, if the patient has conditions that elevate D-dimer (active cancer, recent surgery, pregnancy, advanced age), proceed directly to ultrasound instead 1.

Step 3: Moderate-to-High Pretest Probability (Wells Score ≥2)

Proceed directly to complete duplex ultrasound without D-dimer testing 1, 2:

The American College of Chest Physicians explicitly recommends against using D-dimer as a stand-alone test in high-probability patients because the false-negative rate is unacceptable 1. The prevalence of DVT in this group (17-75%) makes imaging mandatory 1, 3.

Step 4: Complete Duplex Ultrasound Protocol

The ultrasound must be comprehensive from inguinal ligament to ankle 1:

• Compression testing at 2-cm intervals of all deep veins (common femoral, femoral, popliteal, posterior tibial, peroneal veins) 1
• Spectral Doppler waveforms of bilateral common femoral and popliteal veins 1
• Color Doppler imaging 1
• Evaluation of symptomatic areas for superficial thrombosis or alternative diagnoses 1

Critical diagnostic criterion: Normal veins completely collapse under probe pressure; thrombus-containing veins remain non-compressible 1, 2

The Society of Radiologists in Ultrasound consensus strongly recommends against limited proximal-only protocols because they miss 15-20% of calf DVTs that may propagate proximally, requiring inconvenient repeat scanning at 1 week 1.

Step 5: Interpretation and Follow-Up

If ultrasound is positive for proximal DVT (popliteal vein or above):

• Treat immediately with anticoagulation 1, 2
• No confirmatory venography needed 1

If ultrasound shows isolated distal (calf) DVT:

• Two evidence-based options: immediate anticoagulation OR serial ultrasound surveillance at 1 week to detect proximal extension 1, 2
• Favor immediate anticoagulation if severe symptoms, multiple vein involvement, thrombus >5 cm length or >7 mm diameter, or risk factors for extension 2

If ultrasound is negative in low-probability patients with negative D-dimer:

• DVT excluded; no further testing 1

If ultrasound is negative in high-probability patients:

• Repeat proximal ultrasound in 1 week OR obtain whole-leg ultrasound OR perform highly sensitive D-dimer 1
• If repeat testing remains negative, DVT is excluded 1

Common Pitfalls to Avoid

Do not skip pretest probability assessment 1: Performing the same tests on all patients wastes resources and exposes low-risk patients to unnecessary imaging 1.

Do not use D-dimer alone in moderate-to-high probability patients 1: The false-negative rate is too high when prevalence exceeds 17% 1, 3.

Do not accept limited proximal-only ultrasound protocols 1: These require mandatory repeat scanning at 1 week and miss clinically significant calf DVT 1.

Do not order venography 1: Ultrasound has replaced venography as the diagnostic standard due to equivalent accuracy without invasiveness 1.