Key result
Time spent with subtherapeutic INR levels (<2) was associated with a more than three-fold increased risk of VTE recurrence compared to therapeutic INR levels (HR 3.37; 95% CI 2.16-5.27).
Why the study?
Does subtherapeutic INR (<2) increase the risk of recurrent VTE compared to therapeutic INR (2-3) in adults treated with warfarin for VTE?
Cohort (n=1,753)
No
Does subtherapeutic INR (<2) increase the risk of recurrent VTE compared to therapeutic INR (2-3) in adults treated with warfarin for VTE?
Hazard Ratio: 3.37 (95% CI 2.16–5.27)
Subtherapeutic INR levels (<2) during warfarin therapy for VTE are associated with a more than three-fold increased risk of recurrence compared to therapeutic levels, reinforcing the importance of maintaining INR within the target range.
Supports vigilant INR monitoring in warfarin-treated VTE; leaves open whether optimizing TTR reduces recurrence in trials.
OBJECTIVE: Guidelines for warfarin treatment of venous thromboembolism (VTE) recommend targeting an international normalized ratio (INR) level of 2-3. This study examines the association between INR levels and VTE recurrence among warfarin-treated patients. METHODS: A retrospective cohort study in the MedMining electronic health record database included adults treated with warfarin for VTE in 2004-2011. INR levels during warfarin use were categorized as below therapeutic range (<2), in range (2-3), or above range (>3), with time in each category estimated using the Rosendaal method. Recurrent VTE was noted from 30 days after the initial VTE to end of follow-up, which ranged up to 8 years. The incidence of recurrent VTE was calculated, and association with time-varying INR levels estimated using Cox models. RESULTS: Of 1753 qualifying patients, 867 had deep vein thrombosis, and 886 had pulmonary embolism. Mean age was 58 years, and 50.7% were female. Across all follow-up time, VTE recurrences were observed in 134 (7.6%) patients, at a rate of 3.2 (95% confidence interval [CI]: 0.7-9.1) events per 100 person-years. The risk of VTE recurrence was greater during time spent with INR <2 than with INR in the therapeutic range (hazard ratio [HR]: 3.37; 95% CI: 2.16-5.27). Low platelet counts also predicted greater risk of VTE recurrence (HR: 2.13; 95% CI: 1.24-3.67). LIMITATIONS: Exposure to warfarin and other anticoagulants was estimated based on prescription data and may be inaccurate. The study data include care within a single health system; thus, care received outside of the health system may be missing, and results may not be generalizable to the broader US population. CONCLUSIONS: Approximately 8% of patients experienced a recurrent VTE during follow-up. Subtherapeutic INR levels were associated with a more than three-fold increased risk of VTE recurrence.
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Nordstrom et al. (2014) conducted a cohort in Venous thromboembolism (VTE) (n=1,753). Subtherapeutic INR levels (<2) vs. INR in the therapeutic range (2-3) was evaluated on VTE recurrence (HR 3.37, 95% CI 2.16-5.27). Time spent with subtherapeutic INR levels (<2) was associated with a more than three-fold increased risk of VTE recurrence compared to therapeutic INR levels (HR 3.37; 95% CI 2.16-5.27).
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