Management of INR 0.94 on Warfarin
Increase the warfarin dose by 5-20% of the total weekly dose and recheck INR within 3-7 days. 1
Immediate Assessment
An INR of 0.94 indicates subtherapeutic anticoagulation, placing the patient at risk for thromboembolic events while providing inadequate protection. 1 This requires prompt dose adjustment without any role for vitamin K administration. 1
Key steps:
Verify the target INR range for the specific indication (typically 2.0-3.0 for atrial fibrillation, venous thromboembolism, and bileaflet mechanical aortic valves; 2.5-3.5 for mechanical mitral valves). 2, 3
Assess thromboembolic risk during this period of inadequate anticoagulation, particularly in high-risk patients such as those with mechanical mitral valves, recent thromboembolism, or prior stroke while anticoagulated. 1
Identify causes of the low INR: increased dietary vitamin K intake, medication interactions (antibiotics, NSAIDs, herbal supplements), or non-adherence. 1
Dose Adjustment Protocol
Increase the weekly warfarin dose by 5-20% based on how far the INR is from target. 1, 4 For an INR of 0.94 (significantly below the therapeutic range of 2.0-3.0), a 15-20% increase is appropriate. 4
Recheck INR within 3-7 days after dose adjustment to ensure adequate response. 1
Do not use loading doses, as these increase hemorrhagic complications without providing more rapid protection against thrombus formation. 3
Monitor INR 2-4 times per week immediately after dose changes, then gradually lengthen intervals up to 4 weeks once stable. 4
Bridging Anticoagulation Considerations
Bridging with low molecular weight heparin (LMWH) should be considered only in very high-risk patients: 1
- Mechanical mitral valve 1
- Recent thromboembolism within 3 months 1
- History of thromboembolism while anticoagulated 1
For most patients with atrial fibrillation or venous thromboembolism, bridging is not necessary during the brief period of dose adjustment. 1
Critical Pitfalls to Avoid
Never administer vitamin K for subtherapeutic INR. Vitamin K is only indicated for elevated INR values with or without bleeding. 1
Avoid excessive dose increases that could lead to supratherapeutic INR rebound. Most adjustments should alter the weekly dose by 5-20%. 4
Screen for medication interactions including over-the-counter drugs that may be affecting warfarin metabolism. 1
Assess dietary vitamin K consistency, as fluctuations are a common cause of INR instability. 1
Alternative Anticoagulation
If the patient demonstrates persistent inability to maintain therapeutic INR despite dose adjustments, consider switching to a direct oral anticoagulant (DOAC) such as dabigatran, rivaroxaban, or apixaban, which have more predictable dose-response relationships and do not require INR monitoring. 2, 5