Is there still a risk of Deep Vein Thrombosis (DVT) in a patient with elevated International Normalized Ratio (INR) on warfarin (coumarin) presenting with bilateral leg swelling?

DVT Risk Assessment in Warfarin Patient with INR 6.7 and Bilateral Leg Swelling

Yes, DVT remains possible despite the elevated INR of 6.7, and ultrasound evaluation is warranted to rule out DVT in this patient with bilateral leg swelling. 1

Why DVT Can Still Occur Despite Supratherapeutic Anticoagulation

• Warfarin does not provide absolute protection against thrombosis, even at supratherapeutic levels—the drug reduces but does not eliminate clotting risk 1
• The elevated INR of 6.7 indicates excessive anticoagulation that greatly increases bleeding risk (bleeding becomes clinically unacceptable once INR exceeds 5.0), but this does not rule out concurrent thrombosis 1
• Bilateral leg swelling in a patient on warfarin requires investigation regardless of INR level, as multiple etiologies exist including DVT, heart failure, venous insufficiency, or bleeding into soft tissues 2

Clinical Reasoning for Ultrasound

Obtain bilateral lower extremity venous duplex ultrasound to definitively exclude DVT before attributing symptoms to other causes:

• DVT can develop even with therapeutic or supratherapeutic anticoagulation if the patient has had periods of subtherapeutic INR, medication non-adherence, or overwhelming prothrombotic stimulus 3
• The consequences of missing DVT are severe—including pulmonary embolism, chronic venous insufficiency, and death—making diagnostic confirmation essential 3
• Bilateral presentation does not exclude DVT; while less common than unilateral DVT, bilateral thrombosis can occur, particularly in patients with systemic hypercoagulable states 3

Immediate Management Priorities

Address the dangerously elevated INR while pursuing DVT evaluation:

• For INR 6.7 without active bleeding, omit the next 1-2 doses of warfarin and monitor INR closely 2, 4
• Consider oral vitamin K 1.0-2.5 mg given the significantly elevated INR above 5.0, especially if the patient has increased bleeding risk factors 2, 5
• Recheck INR within 24-48 hours to ensure appropriate downward trend 2
• Do not delay ultrasound evaluation while managing the INR—both issues require concurrent attention 2

Critical Differential Considerations

Bilateral leg swelling with elevated INR raises several important possibilities:

• Soft tissue bleeding from excessive anticoagulation can cause leg swelling and may mimic DVT clinically 6
• The bleeding itself can paradoxically elevate INR further, creating a cycle where hemorrhage leads to higher INR readings 6
• Heart failure or venous insufficiency may be exacerbated by the patient's underlying condition requiring anticoagulation 2
• Ultrasound will help differentiate between thrombotic and non-thrombotic causes of swelling 3

Common Pitfalls to Avoid

• Do not assume supratherapeutic INR excludes DVT—anticoagulation failure can occur, and the elevated INR may be recent or intermittent 3
• Do not attribute bilateral swelling to "fluid overload" without imaging, as this delays DVT diagnosis and appropriate treatment 3
• Avoid excessive vitamin K administration (>5 mg) as this can cause warfarin resistance and make re-anticoagulation difficult if DVT is confirmed 4, 5
• Do not withhold ultrasound due to concerns about "unnecessary testing"—the clinical stakes of missed DVT are too high 3

Investigation of INR Elevation

Identify why the INR became supratherapeutic while evaluating for DVT:

• Review recent medication changes, particularly antibiotics, NSAIDs, or other drugs that interact with warfarin 4, 5
• Assess dietary changes affecting vitamin K intake 7
• Consider acute illness (fever, diarrhea, liver dysfunction) that may alter warfarin metabolism 5
• Evaluate medication adherence—accidental double-dosing is common 4