The international normalized ratio. A guide to understanding and correcting its problems

Area of Science:

• Clinical Pathology
• Pharmacology

Background:

• The international normalized ratio (INR) is widely used for monitoring warfarin therapy.
• Identified issues in prothrombin time (PT) testing have raised concerns about INR reliability.
• These problems, highlighted by the INR system, relate to long-standing PT monitoring techniques.

Purpose of the Study:

• To discuss potential problems with the INR system in warfarin monitoring.
• To critically review the clinical relevance of these INR system issues.
• To offer practical solutions for clinicians regarding PT testing.

Main Methods:

• Communication directed to practicing clinicians.
• Discussion of potential problems with the INR system.
• Critical review of the clinical relevance of identified issues.

Main Results:

• Differences in PT reagents and methods currently prevent a perfect INR assay system.
• Clinicians can achieve safe and effective warfarin dosing by adhering to specific PT testing protocols.
• Potential problems with the INR system are identified and their clinical relevance assessed.

Conclusions:

• The INR system's reliability is challenged by PT testing variability.
• A compromise between laboratory expectations and clinical needs is essential for effective warfarin monitoring.
• Safe warfarin dosing is achievable through careful attention to PT testing procedures.