Can a swollen, red ankle and leg in an elderly patient on warfarin (anticoagulant) for atrial fibrillation (A-fib) be a blood clot after an 8-hour airplane trip?

Swollen Red Leg in Warfarin Patient After Air Travel: Diagnostic Approach

This presentation is concerning but paradoxical—while DVT remains possible despite warfarin therapy, cellulitis is actually the more likely diagnosis given the acute onset (1 day) and red appearance, and you must immediately check an INR to assess anticoagulation adequacy before proceeding. 1

Why DVT is Still Possible Despite Warfarin

• Warfarin does NOT eliminate VTE risk, particularly if the INR is subtherapeutic or the patient has additional risk factors 2
• The 8-hour flight created a 2.8-fold increased risk of VTE compared to non-travelers, with risk increasing 18% for each additional 2 hours of flight duration 1
• Air travel-related VTE occurs through the Virchow triad: prolonged immobility causing venous stasis, hypercoagulability from dehydration and cabin hypoxia, and potential endothelial injury 1, 3
• Elderly patients on warfarin for atrial fibrillation remain at elevated baseline thromboembolic risk, and inadequate anticoagulation during travel could permit clot formation 2

Immediate Next Steps (In Order)

1. Check INR Immediately

• If INR is subtherapeutic (<2.0), DVT becomes significantly more likely and warrants urgent imaging 2
• Therapeutic INR (2.0-3.0) makes DVT less likely but does not exclude it 2

2. Apply Wells DVT Score for Risk Stratification

• The Wells score is the validated clinical tool to determine pre-test probability before imaging 4
• Key features to assess:
  • Active cancer (1 point)
  • Paralysis/recent immobilization of lower extremity (1 point)
  • Recently bedridden >3 days or major surgery within 12 weeks (1 point)
  • Localized tenderness along deep venous system (1 point)
  • Entire leg swollen (1 point)
  • Calf swelling >3 cm compared to asymptomatic leg (1 point)
  • Pitting edema confined to symptomatic leg (1 point)
  • Collateral superficial veins (1 point)
  • Previously documented DVT (1 point)
  • Alternative diagnosis as likely or more likely than DVT (-2 points) 4

3. Clinical Features Favoring Cellulitis Over DVT

• Redness (erythema) is MORE characteristic of cellulitis than DVT—DVT typically presents with swelling and pain but less prominent erythema 4
• Warmth, tenderness, and rapid onset (1 day) suggest infection
• If fever, elevated white blood cell count, or skin breakdown present, cellulitis becomes the primary diagnosis 4

4. Obtain D-Dimer if Wells Score is Low

• D-dimer is only useful when Wells score indicates "DVT unlikely" (<2 points) 4
• Negative D-dimer effectively rules out DVT in low-probability patients 4
• D-dimer has limited utility in elderly patients and those with atrial fibrillation due to high false-positive rates

5. Order Duplex Ultrasound for Definitive Diagnosis

• Compression ultrasound with Duplex scanning is the gold standard for DVT diagnosis 4
• Should be performed urgently if:
  • Wells score ≥2 (DVT likely) 4
  • INR is subtherapeutic 2
  • D-dimer is positive 4
• Do not delay imaging if clinical suspicion is high, as pulmonary embolism is a potentially fatal complication 1, 4

Critical Pitfalls to Avoid

• Do not assume warfarin provides complete protection—breakthrough VTE can occur with subtherapeutic INR or in high-risk situations like prolonged air travel 2, 1
• Do not dismiss DVT solely based on erythema—while redness suggests cellulitis, superficial thrombophlebitis or DVT with secondary inflammation can present similarly 4
• Do not rely on D-dimer alone in elderly patients—age increases baseline D-dimer levels, reducing specificity 4
• Do not delay treatment if DVT is confirmed—even patients on warfarin may need bridging with low-molecular-weight heparin if INR is subtherapeutic 2

If DVT is Confirmed

• Ensure therapeutic anticoagulation with INR 2.0-3.0 for atrial fibrillation patients 2
• Consider switching to a direct oral anticoagulant (DOAC) if warfarin management is problematic, as DOACs show similar efficacy with better safety profiles 5
• Evaluate for provoked versus unprovoked DVT—the 8-hour flight represents a transient provoking factor, but underlying thrombophilia should be considered if INR was therapeutic 2

If Cellulitis is Confirmed

• Initiate antibiotics covering Streptococcus and Staphylococcus species
• Elevate the affected limb
• Monitor for systemic signs of infection
• Ensure INR remains therapeutic throughout treatment as infection can affect warfarin metabolism 2