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Standardization of Prothrombin Time/International Normalized Ratio (PT/INR)
Akbar Dorgalaleh1, Emmanuel J Favaloro2, Mehran Bahraini1
1Department of Hematology and Blood Transfusion, School of Allied Medicine, Iran University of Medical Sciences, Tehran, Iran.
International Journal of Laboratory Hematology
|September 26, 2020
Summary
The international normalized ratio (INR) test, crucial for monitoring warfarin therapy, still shows variability between labs. This review offers guidance on international sensitivity index (ISI) verification to improve INR reporting accuracy.
Area of Science:
- Clinical Pathology
- Hematology
- Medical Laboratory Science
Background:
- Prothrombin time (PT) is a standard clinical coagulation test.
- International normalized ratio (INR) standardizes PT results for monitoring vitamin K antagonist therapy.
- INR relies on mean normal PT (MNPT) and international sensitivity index (ISI) for standardization.
Purpose of the Study:
- To review the factors contributing to INR variability in laboratory reporting.
- To provide guidance on appropriate international sensitivity index (ISI) verification and validation.
- To reduce discrepancies in cross-laboratory INR reporting.
Main Methods:
- Narrative review of existing literature and practices.
- Analysis of factors influencing INR calculation and reporting.
- Discussion of ISI harmonization efforts and limitations.
Main Results:
- Despite harmonization efforts, significant INR variability persists between laboratories.
- Reagent/coagulometer-specific ISIs and general ISIs exist, but do not eliminate discrepancies.
- Variations in ISI values among different coagulometer models contribute to reporting errors.
Conclusions:
- Inconsistent INR reporting impacts patient management.
- Proper ISI verification and validation are essential to minimize cross-laboratory reporting variability.
- Implementing standardized ISI practices can enhance the reliability of INR testing.
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