For a patient taking warfarin 5 mg daily with an International Normalized Ratio (INR) of 2.3, a Prothrombin Time (PT) of 23.3 seconds, and an activated Partial Thromboplastin Time (aPTT) of 39 seconds, are these results therapeutic and should the warfarin dose be adjusted?

Warfarin Management for INR 2.3

Your patient's INR of 2.3 is therapeutic and no dose adjustment is needed. The current warfarin 5 mg daily should be continued without modification, with routine monitoring in 2-4 weeks if previously stable 1.

Current Anticoagulation Status

Your patient's results fall squarely within the standard therapeutic range:

• INR 2.3 is therapeutic for most indications including atrial fibrillation, venous thromboembolism, and most mechanical heart valves, where the target range is 2.0-3.0 1, 2
• The PT of 23.3 seconds is appropriately prolonged and correlates with the therapeutic INR 1
• The elevated aPTT of 39 seconds (reference 24-33) is expected and clinically insignificant when on warfarin monotherapy, as warfarin can increase aPTT even without heparin present 2

Dose Management Algorithm

No dose adjustment is indicated based on the following structured approach 3:

• INR 2.0-2.9: Continue current dose without change 3
• INR 1.6-1.9: Would increase by 10% per week 3
• INR 3.0-3.9: Would decrease by 10% per week 3
• INR 4.0-4.9: Would hold 1 dose, then restart with 10% reduction 3

Your patient at INR 2.3 requires no intervention.

Monitoring Frequency

Recheck INR in 2-4 weeks if this patient has been stable on the current dose 1. The American College of Cardiology recommends:

• If previously stable with consistent INRs in therapeutic range, extend monitoring intervals to 4 weeks 1
• The American College of Chest Physicians supports intervals up to 12 weeks for patients with reliably stable INR patterns 1, 3
• Resume more frequent monitoring (weekly or biweekly) only if dose adjustments are made, new medications are started, or intercurrent illness occurs 1, 3

Critical Pitfalls to Avoid

Do not overreact to therapeutic INR values within range. Common errors include:

• Making unnecessary dose adjustments when INR is therapeutic but not exactly at the midpoint (2.5) - any value between 2.0-3.0 is acceptable 1
• Ignoring the elevated aPTT - warfarin routinely prolongs aPTT, and this finding does not indicate over-anticoagulation or require intervention unless aPTT exceeds 50 seconds with bleeding 2
• Testing too frequently once stable - excessive monitoring increases costs without improving outcomes and may lead to unnecessary dose changes from normal INR fluctuation 1

When to Adjust Warfarin Dose

Future dose adjustments would only be warranted if:

• INR <1.5: Increase weekly dose by 15% 3
• INR 1.6-1.9: Increase weekly dose by 10% 3
• INR 3.0-3.9: Decrease weekly dose by 10% 3
• INR 4.0-4.9 without bleeding: Hold one dose, then restart at 10% lower weekly dose 3
• INR ≥5.0 without bleeding: Hold until INR returns to 2-3, then restart at 15% lower weekly dose 3

Special Considerations

Maintain consistent vitamin K intake - fluctuations in dietary vitamin K (dark green vegetables, certain oils) can cause INR variability and should be kept stable rather than avoided 1, 3.

Monitor for drug interactions when adding or stopping medications, particularly antibiotics, NSAIDs, antidepressants, and statins, as these commonly alter warfarin metabolism 1.

The reference range note about "non-anticoagulated patients" on the lab report (INR 0.9-1.2) is irrelevant for your patient who is intentionally anticoagulated - disregard this and focus on the therapeutic target of 2.0-3.0 1, 2.