Evaluation of Frozen Plasma Calibrants for Enhanced Standardization of the International Normalized Ratio (INR): A Multi-Center Study

Dorothy M. Adcock; Marilyn Johnston

doi:10.1055/s-0037-1612946

Thrombosis and Haemostasis, Table of Contents

Thromb Haemost 2002; 87(01): 74-79
DOI: 10.1055/s-0037-1612946

Review Article

Schattauer GmbH

Evaluation of Frozen Plasma Calibrants for Enhanced Standardization of the International Normalized Ratio (INR): A Multi-Center Study

Dorothy M. Adcock

¹Medical/Laboratory Director, Esoterix Coagulation, Department of Preventive Medicine and Research, Colorado Permanente Medical Group, Canada

,

Marilyn Johnston

²Hamilton Civic Hospitals Research Centre, Hamilton, ON, Canada

› Author Affiliations

Abstract

Summary

Local ISI calibration has been proposed to improve INR accuracy and inter-laboratory precision. We evaluated the affect of local PT calibration on INR precision and accuracy using six levels of frozen plasma calibrants prepared and pooled from normal donors and patients stabilized on sodium warfarin (coumarin) based oral anticoagulant therapy (OAT). Reference prothrombin time (PT) and INR values were assigned to these calibrants in accordance with World Health Organization (WHO) procedure using rTF 95 international reference preparation (IRP) of thromboplastin (human recombinant). These calibrants, along with five similarly characterized individual OAT patient plasmas, were distributed to 127 laboratories in a multi-center study. Calibrant plasmas were evaluated and INR’s subsequently determined on the 5 OAT test samples using: 1) the ISI and MNPT in place before the study (the local system), 2) the locally calibrated ISI value (local system with ISI calibration) and 3) a PT-INR calibration curve. Precision of INR results improved across the study group using the local system with ISI calibration and the PT-INR calibration curve methods, while accuracy of INR results improved using the PT-INR calibration curve approach only and not the local ISI calibration. The authors conclude that frozen plasma calibrants can be used locally to enhance precision and accuracy of PT results as reported in INR. These calibrants are effective over a range of reagents and instrument combinations. Furthermore, the PT-INR calibration curve appears to be the superior method for local calibration.

Keywords

Prothrombin time - INR - plasma calibrants - local calibration - oral anticoagulant therapy

Full Text

References

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