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[Inter-institute variations in International Normalized Ratio and thrombotest]
1Second Department of Internal Medicine, Toyama Medical and Pharmaceutical University.
Insights
Oral anticoagulant therapy monitoring in Japanese patients requires careful consideration of monitoring methods. The study recommends using the International Normalized Ratio (INR) with low International Sensitivity Index (ISI) thromboplastin for accurate and consistent results.
Area of Science:
- Cardiology and Thrombosis Research
- Pharmacology and Therapeutics
- Clinical Laboratory Science
Context:
- Oral anticoagulant therapy is crucial for preventing thromboembolic events in patients with atrial fibrillation and other heart conditions.
- Optimal anticoagulation intensity for high-risk patients, particularly in Japan, remains unclear, balancing efficacy and bleeding risk.
- The Toyama Warfarin Rational Dosage (TOWARD) study aimed to define optimal anticoagulant therapy levels.
Purpose:
- To investigate the relationship between Thrombotest (TT) and International Normalized Ratio (INR) values.
- To clarify inter-institute variations in anticoagulant monitoring methods.
- To determine the most reliable method for monitoring oral anticoagulant therapy in Japanese patients.
Summary:
- The relationship between TT and INR is hyperbolic, with INR changes being less pronounced at TT levels above 20%.
- Significant inter-institute variations were observed with TT, but these decreased substantially when a standard reference was used.
- INR measurements showed minimal inter-institute variation, especially when using thromboplastin with an International Sensitivity Index (ISI) below 1.5.
Impact:
- The study suggests that while TT is widely used in Japan, INR monitoring using low ISI thromboplastin is recommended for greater consistency and international standardization.
- Findings contribute to optimizing anticoagulant therapy management, potentially improving patient outcomes by reducing thromboembolic events and bleeding complications.
- Highlights the importance of standardized laboratory practices and reagent selection in ensuring reliable therapeutic drug monitoring.
Abstract:
Oral anticoagulant therapy is effective for reducing the risk of thromboembolic events in patients with atrial fibrillation or other heart diseases. However, the intensity of oral anticoagulation therapy required in high risk patients, especially in Japanese patients, to achieve the best balance between the prevention of thromboembolic events and bleeding complications remains unclear. The multicenter study of Toyama Warfarin Rational Dosage (TOWARD) was started in 1996 to determine the optimal level of anticoagulant therapy. This study investigated the relationship between values of thrombotest (TT) and International Normalized Ratio (INR) measured from the same samples to clarify inter-institute variations. The relationship between TT and INR was not linear but hyperbolic. Changes of INR to TT are relatively small in the TT range of more than 20% as compared with the range of 20% or less. There were considerable inter-institute variations of TT, and the coefficient of variation (CV) was 0.16 and 0.24 in the low level and high level anticoagulation samples, respectively. However, the variations became significantly small when the same reference was used. The CV of INR was 0.12 and 0.08 in the high level and low level anticoagulation samples, respectively, and very similar with the control samples without anticoagulation (0.11). The variation was small when INR was obtained from the international sensitivity index (ISI) of thromboplastin less than 1.5. TT is widely used for monitoring oral anticoagulant therapy in Japan, and is an excellent system with little inter-institute variation when a standard reference is offered. Since INR has been established as an international monitoring system, the use of INR measured with thromboplastin of small ISI is recommended for monitoring.