[Inter-institute variations in International Normalized Ratio and thrombotest]

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.