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1 ECAA Central Facility, School of Biological Sciences, The University of Manchester, Manchester M13 9PT, United Kingdom.
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 Clinical Haematology, Manchester Royal Infirmary, Oxford Road, Manchester, M13 9WL Manchester, United Kingdom.
5 Department for Thrombosis Research, University of Southern Denmark and Department of Clinical Biochemistry, Ribe County Hospital, DK-6700 Esbjerg, Denmark.
aAuthor for correspondence. Fax 44-161-275-5316; e-mail ecaa{at}man.ac.uk.
Background: The International Sensitivity Index (ISI) calibration of whole-blood prothrombin time (PT) monitors for point-of-care testing (POCT) described by Tripodi et al. (Thromb Haemost 1993;70:921–4) has been shown to be dependable but is too complex and demanding. The use of plasma would simplify calibration of whole-blood POCT PT monitors, but important differences may exist between the ISI for whole blood and plasma calibrations.
Methods: In a 10-center calibration study of two POCT whole-blood monitoring systems (CoaguChek Mini and TAS PT-NC), we characterized the relationship between the log PT for whole blood and fresh plasma with use of single lots of test strips/cards. This relationship (linear) was used to correct the difference between the whole-blood and plasma ISI. The reliability of the correction with different lots of test strips/cards was assessed at three centers. The linear relationship was used to correct the difference in the whole-blood and plasma ISI with four other lots of TAS PT-NC cards and with two additional lots of CoaguChek Mini test strips.
Results: The correction decreased the ISI difference from 13.3% to 0.9% for the TAS PT-NC and from 5.7% to 0.6% for the CoaguChek Mini. In assessments at three centers, which included different lots of test strips/cards, the mean ISI difference was markedly decreased with the TAS PT-NC but not with the CoaguChek Mini, for which the mean ISI difference increased slightly.
Conclusions: The proposed correction resolves the discrepancy between whole-blood and fresh plasma ISI calibrations with TAS PT-NC test cards. The CoaguChek Mini systems could be calibrated without this correction.
The following articles in journals at HighWire Press have cited this article:
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  L. Poller, J. Jespersen, M. Keown, S. Ibrahim, and A. Tripodi The authors of the article cited above respond: Clin. Chem., August 1, 2007; 53(8): 1556 - 1557. [Full Text] [PDF]
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L. Poller, M. Keown, N. Chauhan, A. M.H.P. van den Besselaar, A. Tripodi, C. Shiach, and J. Jespersen European Concerted Action on Anticoagulation. Quality Assessment of the CoaguChek Mini and TAS PT-NC Point-of-Care Whole-Blood Prothrombin Time Monitors Clin. Chem., March 1, 2004; 50(3): 537 - 544. [Abstract] [Full Text] [PDF]
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 L. Poller, M. Keown, N. Chauhan, A. M. van den Besselaar, A. Tripodi, C. Shiach, and J. Jespersen Reliability of international normalised ratios from two point of care test systems: comparison with conventional methods BMJ, July 3, 2003; 327(7405): 30. [Abstract] [Full Text] [PDF]
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 L Poller, M Keown, N Chauhan, A M H P van den Besselaar, A Tripodi, C Shiach, and J Jespersen European Concerted Action on Anticoagulation (ECAA). An assessment of lyophilised plasmas for ISI calibration of CoaguChek and TAS whole blood prothrombin time monitors J. Clin. Pathol., February 1, 2003; 56(2): 114 - 119. [Abstract] [Full Text] [PDF]
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