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European Concerted Action on Anticoagulation (ECAA). An assessment of lyophilised plasmas for ISI calibration of CoaguChek and TAS whole blood prothrombin time monitors

¹ ECAA Central Facility, School of Biological Sciences, The University of Manchester, Manchester M13 9PT, UK
² Haemostasis and Thrombosis Research Centre, Leiden University Medical Center, 2333 ZA Leiden, The Netherlands
³ A Bianchi Bonomi, Haemophilia and Thrombosis Centre, IRCCS Maggiore Hospital, University of Milan, 20122 Milan, Italy
⁴ Department of Haematology, Manchester Royal Infirmary, Manchester M13 9WL, UK
⁵ Department for Thrombosis Research, University of Southern Denmark and Department of Clinical Biochemistry, Ribe County Hospital, Esbjerg DK-6700, Denmark

Correspondence to:
Professor L Poller, ECAA Central Facility, School of Biological Sciences, The University of Manchester, Manchester M13 9PT, UK;
ecaa{at}man.ac.uk

Aims: The recommended method for the international sensitivity index (ISI) calibration of whole blood point of care testing (POCT) prothrombin time (PT) systems was originally described by Tripodi et al in 1993 but is too complex and demanding. The present European Concerted Action on Anticoagulation (ECAA) study aimed to assess the reliability of simpler ISI calibration using lyophilised plasma samples.

Methods: ISI calibrations using three different types of ECAA lyophilised plasma samples (artificially depleted, individual, and pooled coumarin) were compared with whole blood calibrations on CoaguChek Mini and TAS PT-NC POCT monitors at 10 centres.

Results: With CoaguChek Mini systems, lyophilised coumarin plasma samples (both single donation and pooled) gave ISI and international normalised ratio (INR) values comparable to whole blood. With artificially depleted plasma, ISI and INR values were too high. With TAS PT-NC systems, all three types of lyophilised plasma samples gave inaccurate ISI and unreliable INR results, similar to previous ECAA findings with fresh plasma calibrations.

Conclusions: With CoaguChek Mini systems, ISI calibration can be simplified by the use of ECAA lyophilised plasma samples from coumarin treated patients. Further study is needed to devise a simpler calibration method for the TAS PT-NC system.

Keywords: prothrombin time; international sensitivity index; certified lyophilised plasmas; point of care test monitors

Abbreviations: ECAA, European Concerted Action on Anticoagulation; CV, coefficient of variation; INR, international normalised ratio; IRP, international reference preparation; ISI, international sensitivity index; MNPT, mean normal prothrombin time; POCT, point of care testing; PT, prothrombin time; RBT/90, rabbit plain international reference preparation; rTF/95, human recombinant international reference preparation; WHO, World Health Organisation

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