Management of Subtherapeutic INR 1.44 on Warfarin
Increase your weekly warfarin dose by 10-20% and recheck the INR within 3-7 days, as this subtherapeutic level provides inadequate anticoagulation protection and requires dose adjustment. 1
Immediate Actions
- Do not administer vitamin K for subtherapeutic INR—vitamin K is only indicated for elevated INR values with or without bleeding, not for low INR 1
- Verify the indication for anticoagulation (atrial fibrillation, DVT/PE, mechanical valve) and confirm the target INR range is 2.0-3.0 1, 2
- Do not initiate bridging anticoagulation with heparin or LMWH for a single subtherapeutic INR in stable patients, as the American College of Chest Physicians recommends against routinely administering bridging therapy (Grade 2C) 3
Dose Adjustment Strategy
- The American College of Cardiology recommends increasing the weekly warfarin dose by 5-20% for INR 1.44, which is significantly below the therapeutic range of 2.0-3.0 1
- Calculate your patient's total weekly warfarin dose and increase it by 10-15% as a starting point (e.g., if taking 5 mg daily = 35 mg/week, increase to 38.5-40 mg/week) 1
- Recheck INR within 3-7 days to assess response to dose adjustment 1
Identify Contributing Factors
- Screen for medication interactions including antibiotics, NSAIDs, and herbal supplements that may be affecting warfarin metabolism 1
- Assess dietary vitamin K intake consistency, as increased consumption of vitamin K-rich foods (leafy greens, broccoli) is a common cause of INR instability 1
- Review medication adherence and any recent changes in concurrent medications 1
Thromboembolic Risk Assessment
The risk of thromboembolism during this brief period of subtherapeutic anticoagulation is low. A retrospective study of 2,597 patients found only 0.4% thromboembolism rate in the 90 days following a subtherapeutic INR, with no significant difference compared to patients maintaining therapeutic INR 4. This evidence supports avoiding bridging therapy in most patients.
Special Considerations for High-Risk Patients
Consider bridging anticoagulation with LMWH only in very high-risk patients 1:
- Mechanical mitral valve prosthesis
- Recent thromboembolism within 3 months
- History of thromboembolism while anticoagulated
- Caged ball or caged disk mechanical valves
For the vast majority of patients with atrial fibrillation or remote VTE history, bridging is not indicated for a single low INR 3.
Follow-Up Protocol
- Recheck INR within 3-7 days after dose adjustment 1
- Once INR returns to therapeutic range (2.0-3.0), continue monitoring at standard intervals 3
- If INR remains subtherapeutic after dose adjustment, consider further increase of 10-15% and investigate additional contributing factors 1
Common Pitfalls to Avoid
- Never give vitamin K for low INR—this is a critical error that will further suppress anticoagulation 1
- Avoid over-aggressive dose increases exceeding 20% weekly, as this can lead to supratherapeutic INR overshoot 1
- Do not routinely bridge with heparin, as the American College of Chest Physicians found no significant difference in thromboembolic events between bridged and non-bridged patients with single subtherapeutic INR values (Grade 2C recommendation) 3
- Ensure you are addressing the underlying cause (diet, medications, adherence) rather than simply chasing the INR with dose adjustments 1