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Discrepancies in international normalized ratio results between instruments: a model to split the variation into
Una Ø Sølvik1, Per H Petersen, Grete Monsen
1Department of Public Health and Primary Health Care, Faculty of Medicine and Dentistry, University of Bergen, Norway. una.solvik@isf.uib.no
Clinical Chemistry
|August 6, 2010
Summary
Differences in international normalized ratio (INR) measurements between devices are significant. Patient-specific factors contribute to variations, recommending consistent use of a single INR device per patient for reliable monitoring.
Area of Science:
- Clinical Chemistry
- Medical Devices
- Hematology
Background:
- Significant variations in international normalized ratio (INR) measurements between different instruments exceed expected analytical imprecision.
- Understanding the sources of these discrepancies is crucial for accurate patient management.
Purpose of the Study:
- To quantify the subcomponents of variation contributing to differences in INR measurements across multiple devices.
- To investigate the impact of patient-specific factors on INR measurement variability.
Main Methods:
- Compared INR measurements from one laboratory and three point-of-care instruments using blood samples from 36 warfarin-treated outpatients.
- Employed linear regression to correct for systematic deviations and ANOVA for nested design to partition variation into between-subject, within-subject, and analytical components.
Main Results:
- Mean differences between instruments ranged from 1.0% to 14.3%.
- Between-subject variation (CV) ranged from 3.3% to 7.4%, while within-subject variation was consistently around 5%.
- Analytical imprecision varied between 3.8% and 8.6%.
Conclusions:
- INR measurement differences are attributable to calibration, patient-specific variations (between- and within-subject), and analytical imprecision.
- Patient plasma effects likely drive between- and within-subject variations, causing INR differences to fluctuate over time for individual patients.
- Consistent use of a single INR instrument type per patient and site is recommended to minimize monitoring variability.
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