Yonsei Med J.  2009 Feb;50(1):83-88. 10.3349/ymj.2009.50.1.83.

How Well Does the Target INR Level Maintain in Warfarin-Treated Patients with Non-ValvularAtrial Fibrillation?

• Kim JH
• Song YB
• Shin DH
• Kim JS
• Choi JO
• On YK
• Kim JS

• KMID: 1782972
• DOI: http://doi.org/10.3349/ymj.2009.50.1.83

Abstract

PURPOSE
Although warfarin is an effective oral anticoagulation (OAC) drug to reduce the risk of thromboembolism in patients with non-valvular atrial fibrillation (NVAF), long term follow-up data are scarce to be certain whether the target INR level is maintained in warfarin-treated patients in Korea. The aim of this study was to evaluate how well INRs are maintained within the target range using a new index, INR stability (= 100 x number of INRs within target range/total number of INR measurements) which we made, and to find out any correlation between thromboembolic events and INR stability.
MATERIALS AND METHODS
This study was an observational analysis of retrospectively collected data of 129 patients with NVAF from April 2000 to December 2005 at a single tertiary hospital. All patients were registered at the anticoagulation service.
RESULTS
The median duration of follow up was 2.03 years (interquartile range 1.35 - 2.96). During the follow-up period, 60.9 +/- 14.9% of the INR were within the target INR range. INR stability was not significantly different between patients without and with stroke (61.2 +/- 15.0% vs 53.3 +/- 4.9%). Among the known factors affecting fluctuations of the INR value, the most frequent factor was noncompliance (41.8%).
CONCLUSION
The present study showed that it was not enough to maintain INR values within the target range in warfarin-treated patients with NVAF even at a tertiary hospital. Noncompliance is an important problem which interferes with maintaining target INR range.

Keyword

Anticoagulation; atrial fibrillation

MeSH Terms

Adult
Age Factors
Aged
Aged, 80 and over
Anticoagulants/*therapeutic use
Atrial Fibrillation/*drug therapy/epidemiology/etiology
Drug Monitoring/methods
Female
Follow-Up Studies
Heart Valves
Humans
*International Normalized Ratio
Male
Middle Aged
Patient Compliance
Retrospective Studies
Risk Factors
Thrombosis/*blood/epidemiology/*prevention & control
Warfarin/*therapeutic use

Figure

• 

  Fig. 1 Distribution of INRs of all patients. INR stability was defined as a percentage of the value derived by dividing the numbers within the target INR range by the number of all prothrombin time assessments after first achievement of adequate INR range. Blue color expresses % duration within the target INR range, represented as 2 ≤ INR ≤ 3. Red color expresses % duration below the target range represented as < 2 of INR. Green color expresses % duration above the target range represented as > 3 of INR. INR, international normalized ratio.

• 

  Fig. 2 Factors affecting INR stability. Unknown occasion 52.8%, Noncompliance 19.8%, Food 13.2%, Drug 10.0%, Alcoholic beverage 3.1%, Herbal remedy 1.1%. INR, international normalized ratio.

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  Fig. 3 Comparison of INR stability between patients without stroke (n = 125) and those with stroke (n = 4). INR, international normalized ratio.

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  Fig. 4 Correlation between weekly warfarin dose and age. p < 0.001.

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