Simplified Method for International Normalized Ratio (INR) Derivation Based on the Prothrombin Time/INR Line: An International Study

Author:

Poller Leon1,Ibrahim Saied1,Keown Michelle1,Pattison Albert2,Jespersen Jørgen3

Affiliation:

1. European Action on Anticoagulation (EAA) Central Facility, Faculty of Life Sciences, University of Manchester, Oxford Road, Manchester, UK

2. Hart Biologicals Ltd., Hartlepool, UK

3. Department of Clinical Biochemistry, Hospital of South West Denmark, Esbjerg, and Department for Thrombosis Research, Institute of Public Health, University of Southern Denmark, Esbjerg, Denmark

Abstract

BACKGROUND The need to perform local International Sensitivity Index (ISI) calibrations and in particular the requirement for a manual method for prothrombin time (PT) determination, have proved to be obstacles to application of the WHO scheme for PT standardization. METHODS We used international normalized ratio (INR) derived with a set of only 5 European Concerted Action on Anticoagulation (ECAA) lyophilized calibrant plasmas, certified manually by expert centers with reference thromboplastins, to determine a local PT/INR Line. We compared results of an independent set of validation plasmas with INRs from conventional ISI calibrations and with manually certified INRs. RESULTS The mean certified INR of 5 lyophilized validation plasmas was 2.41 with human thromboplastin, 2.04 with bovine/combined, and 2.80 with rabbit. With 42 human reagents, the mean observed INR of the validation plasmas was 2.68 (11.2% deviation from certified INR). Deviation was reduced to 0.4% with both local ISI calibration and the PT/INR Line. Eight results based on bovine/combined thromboplastin gave an INR deviation of 4.9%, becoming 0.5% after ISI calibration and 2.4% with the PT/INR Line. Six results with rabbit reagents deviated from certified INR by 2.5%. After ISI calibration, deviation became 1.1%, and with the PT/INR Line, 0.7%. The PT/INR Line gave similar results with both linear and orthogonal regression analysis. The total proportion of validation plasmas giving INR within 10% deviation from certified values was 42.5% with uncorrected INR, which increased to 92.1% with local ISI calibration and 93.2% with the PT/INR Line. CONCLUSIONS The PT/INR Line procedure with 5 ECAA calibrant plasmas successfully substitutes for local ISI calibrations in deriving reliable INRs.

Publisher

Oxford University Press (OUP)

Subject

Biochemistry (medical),Clinical Biochemistry

Reference32 articles.

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2. International Normalised Ratios (INR): the first 20 years;Poller;J Thromb Haemostas,2004

3. A method to determine the optimum intensity of oral anticoagulant therapy;Rosendaal;Thromb Haemost,1993

4. Comparison of two automated coagulometers and the manual tilt tube method for the determination of prothrombin time;D'Angelo;Am J Clin Pathol,1989

5. Effect of automation on the prothrombin time test in NEQAS surveys;Poller;J Clin Pathol,1989

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