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Local INR correction: justification for a simplified approach
S Craig1, K J Stevenson, J M Dufty
1Throbosis Reference Centre, Withington Hospital, Manchester, UK.
Journal of Clinical Pathology
|December 9, 1997
Summary
Correcting International Normalized Ratio (INR) reporting errors is possible using System International Sensitivity Index (System ISI) methods. The simplest approach involves plotting log reference INR against log local prothrombin time.
Area of Science:
- Clinical Pathology
- Laboratory Medicine
- Medical Diagnostics
Background:
- International Normalized Ratio (INR) reporting errors can impact patient care.
- The System International Sensitivity Index (System ISI) offers a potential solution for INR correction.
- Standardization of INR measurements across different laboratories is crucial.
Purpose of the Study:
- To evaluate the effectiveness of various procedures for correcting INR reporting errors.
- To assess the validity of using System ISI for INR calibration.
- To identify the most reliable and simplest method for INR correction.
Main Methods:
- Prothrombin times were measured for multiple calibrants and plasmas across 57 international centers.
- Different regression analyses (linear and orthogonal) were applied to test various data relationships.
- Calibrations were performed using international reference preparations and a four-center exercise.
Main Results:
- Uncorrected INR data showed a mean deviation of 19.0% and high variability (CV 11.30-17.29%).
- All tested methods successfully reduced INR variability (CV < 7%).
- Specific regression methods, particularly log-log plots, demonstrated the best fit and accuracy for INR correction.
Conclusions:
- INR correction is achievable using multiple methods, including System ISI assignment.
- The simplest and effective method involves linear regression of log reference INR against log local prothrombin time.
- Accurate INR reporting is essential for effective anticoagulant therapy management.