What is the next step for a patient with an unprovoked Deep Vein Thrombosis (DVT) who has completed 3 months of warfarin (coumarin) therapy, is tolerating it well, and has a current International Normalized Ratio (INR) of 2.5?

Continue Warfarin Indefinitely

For this patient with unprovoked DVT who has completed 3 months of warfarin with good tolerance and therapeutic INR, the next step is to continue warfarin indefinitely with periodic reassessment of risks and benefits. 1

Rationale for Indefinite Anticoagulation

High Recurrence Risk in Unprovoked DVT

• Patients with unprovoked venous thromboembolism have an annual recurrence risk exceeding 5% after stopping anticoagulation 1, 2
• This recurrence risk substantially outweighs the bleeding risk associated with well-managed warfarin therapy in patients with low to moderate bleeding risk 1
• The American Heart Association provides Class I, Level A evidence that patients with unprovoked DVT should receive at least 6 months of anticoagulation and be considered for indefinite therapy 1

Minimum Treatment Duration Not Yet Met

• The CHEST guidelines recommend at least 3 months of initial treatment, but this represents the minimum, not optimal duration 1
• Multiple guidelines specify that unprovoked proximal DVT requires 3-6 months of initial therapy before even considering whether to extend treatment 1
• The FDA label for warfarin recommends at least 6-12 months for first episode idiopathic DVT 3

Patient-Specific Favorable Factors

• Good tolerance of warfarin: No bleeding complications during initial 3 months 1
• Therapeutic INR control: Current INR of 2.5 is optimal (target range 2.0-3.0) 1, 3
• No high-risk bleeding features: Young enough (implied by lack of mentioned comorbidities), no history of bleeding, no concurrent antiplatelet therapy 1

Why Not the Other Options

Why Not Stop at 3 Months

• Stopping at 3 months is only appropriate for provoked DVT with reversible risk factors (surgery, trauma) 1
• Research demonstrates that extending treatment beyond 6 months in unprovoked DVT reduces recurrence during the treatment period, though benefit diminishes after stopping 4

Why Not Stop at 6 Months Then Discontinue

• While 6 months represents a reasonable minimum treatment duration, the high recurrence risk (>5% annually) after stopping therapy justifies indefinite treatment in patients tolerating anticoagulation well 1, 2
• The ISTH guidance explicitly states that unprovoked PE or proximal DVT should be considered for anticoagulation "as long as the perceived risk of anticoagulant-related bleeding is not so high as to preclude continued treatment" 1

Why Not Investigate for Thrombophilia Before Deciding

• Thrombophilia testing does not change management in unprovoked DVT—these patients warrant extended anticoagulation regardless of thrombophilia results 5, 6
• The decision for indefinite anticoagulation is based on the unprovoked nature of the event, not on identifying specific thrombophilic conditions 1

Practical Management Algorithm

Immediate Action

• Continue current warfarin regimen maintaining INR 2.0-3.0 1, 3
• Schedule follow-up at 6 months (completing minimum recommended initial treatment duration) 1

At 6-Month Reassessment

• Evaluate for any bleeding episodes or complications during months 3-6 1
• Assess INR control quality (time in therapeutic range) 1, 7
• If still tolerating well with good INR control, continue indefinitely 1

Ongoing Monitoring

• Annual reassessment of risk-benefit ratio is mandatory for all patients on extended anticoagulation 1, 2
• Monitor for new bleeding risk factors: advancing age, need for antiplatelet therapy, development of renal/hepatic impairment 1
• Assess patient adherence, understanding of therapy, and willingness to continue 1

Critical Caveats

When to Reconsider Indefinite Therapy

• Development of high bleeding risk features (recurrent falls, need for dual antiplatelet therapy, severe thrombocytopenia) 1
• Patient preference to stop after informed discussion of recurrence risk 1
• Poor INR control despite optimal management efforts 1, 7

Monitoring Quality Indicators

• Patients with better INR control (higher time in therapeutic range) have lower rates of both recurrence and bleeding 1, 7
• INR values consistently below 2.0 are associated with incomplete thrombus resolution and higher recurrence risk 7

Alternative Considerations

• If warfarin becomes problematic, direct oral anticoagulants (DOACs) are reasonable alternatives for extended therapy, though not specifically addressed in your question 1
• Consider compression stockings for 2 years to reduce post-thrombotic syndrome risk 1