Management of INR 3.3 on Warfarin

For an INR of 3.3 without bleeding, continue your current warfarin dose without any adjustment and recheck the INR in 1-2 weeks. 1

Rationale for No Dose Adjustment

An INR of 3.3 represents only a marginal elevation above the standard therapeutic range of 2.0-3.0 for most indications (atrial fibrillation, venous thromboembolism). 1
Bleeding risk does not become clinically significant until INR exceeds 3.5, and intracranial hemorrhage risk specifically does not rise appreciably until INR surpasses this threshold. 1
A high-quality randomized controlled study demonstrated that maintaining the same warfarin dose for asymptomatic patients with INR ≤3.3 is safe, with only one minor bleeding event (epistaxis) occurring in 103 patients over 30 days of follow-up. 2
In this same study, patients who maintained their dose were more likely to have follow-up INR values in the therapeutic range (2.0-3.0) compared to those who reduced their dose, particularly when the initial INR was 3.2 or 3.3. 2

Reduce your weekly warfarin dose by 10% only if: 1

The INR is consistently >3.0 on multiple consecutive measurements, or
The INR exceeds 3.5, or
You have high bleeding-risk factors including age >75 years, prior bleeding history, concurrent antiplatelet therapy, renal impairment, or significant alcohol use. 1

Vitamin K should NOT be administered for an INR of 3.3 in the absence of bleeding. 1
Vitamin K is only indicated when INR exceeds 5.0 in asymptomatic patients without bleeding. 1

Recheck INR within 1-2 weeks after maintaining the current dose. 1, 2
If the repeat INR remains in the 3.0-3.5 range on multiple measurements, then consider a 10% reduction in weekly warfarin dose. 1

Before making any dose changes, investigate potential causes of the mild INR elevation: 1

Recent medication changes or additions, particularly antibiotics which can dramatically alter INR even if taken intermittently 3
Dietary changes in vitamin K intake, including changes in cooking oils (canola oil contains 141 μg vitamin K/100g vs. corn oil with only 2.91 μg/100g) 3
Intercurrent illness, including fever, hepatic dysfunction, congestive heart failure, or thyroid disorders 3
Unreported over-the-counter medications or herbal supplements 3
Changes in alcohol consumption 1

Avoid unnecessary dose reductions for single INR values of 3.2-3.3, as this often leads to subtherapeutic anticoagulation on follow-up. 2
Never reduce warfarin dose by >20% for mildly elevated INRs, as this causes excessive INR drops (median follow-up INR of 1.7 with 21-43% dose reductions vs. 2.7 with maintained dose). 2
Do not make dramatic dose changes based on a single out-of-range value, as this may simply reflect normal dietary variation. 1

For patients with mechanical prosthetic heart valves and INR 3.3 without bleeding, the same approach applies—maintain the current dose and monitor closely. 1
These patients require careful consideration of thromboembolism risk, though bridging anticoagulation is rarely necessary at INR 3.3. 1