What are the next steps for a patient with foot and ankle symptoms after a long flight to rule out DVT?

Diagnostic Workup for Foot and Ankle Symptoms After Long Flight

For a patient with isolated foot and ankle symptoms after a long flight, begin with clinical probability assessment using the Wells score, followed by a highly sensitive D-dimer test if the pretest probability is low to moderate. 1, 2

Clinical Probability Assessment

• Apply the Wells score immediately to stratify DVT risk into low (5% prevalence), moderate (17% prevalence), or high (53% prevalence) categories. 1, 2
• Isolated foot and ankle pain without leg swelling or redness significantly reduces the likelihood of DVT, as these cardinal signs are typically present in acute DVT. 2
• Long-haul flights >4 hours increase DVT risk twofold, with risk increasing 18% for each additional 2 hours of flight duration. 1

Diagnostic Algorithm Based on Pretest Probability

Low Pretest Probability (Wells Score Low)

• Order a highly sensitive D-dimer test first. 1
• If D-dimer is negative, DVT is excluded and no further testing is needed. 1, 2
• If D-dimer is positive, proceed to compression ultrasound of the proximal veins. 1

Moderate Pretest Probability

• Either highly sensitive D-dimer or proximal compression ultrasound (CUS) can be used as the initial test. 1, 3
• A negative highly sensitive D-dimer excludes DVT without need for imaging. 1, 2
• If proximal CUS is negative, no further testing is required. 1

High Pretest Probability

• Proceed directly to compression ultrasound without D-dimer testing, as D-dimer should not be used as a stand-alone test in high-risk patients. 1, 3
• If proximal CUS is negative but clinical suspicion remains high, perform repeat proximal CUS in 1 week or whole-leg ultrasound. 1, 3

Imaging Considerations

• Compression ultrasound is the preferred imaging modality, assessing compressibility of femoral and popliteal veins. 1, 3
• Whole-leg ultrasound may be preferred if the patient cannot return for serial testing or has severe symptoms consistent with calf DVT. 1, 3
• If there is extensive unexplained leg swelling and proximal ultrasound is negative with positive D-dimer, image the iliac veins to exclude isolated iliac DVT. 1, 3

Common Pitfalls to Avoid

• Do not rely on clinical features alone for diagnosis, as symptoms of DVT are notoriously non-specific. 1, 3
• Do not use D-dimer in high pretest probability patients as the sole test to rule out DVT. 1, 3
• Do not assume isolated foot/ankle symptoms without leg swelling represent DVT without proper risk stratification, as DVT typically presents with more proximal symptoms. 2
• Consider alternative diagnoses such as muscle strain, superficial thrombophlebitis, or nerve compression if D-dimer is negative and no DVT signs are present. 2

When to Escalate Testing

• Perform ultrasound if leg swelling develops or symptoms worsen despite a negative D-dimer. 2
• If ultrasound is impractical (leg casting, excessive subcutaneous tissue) or nondiagnostic, consider CT venography, MR venography, or MR direct thrombus imaging as alternatives. 1, 3