Guidelines on preparation, certification, and use of ce...

Guidelines on preparation, certification, and use of certified plasmas for ISI calibration and INR determination

Guidelines on preparation, certification, and use of certified plasmas for ISI calibration and INR determination
November 2004
A. M. H. P. Van Den Besselaar, T. W. Barrowcliffe*, L. L. Houbouyan-R?veillard, J. Jespersen, M. Johnston?, L. Poller? and A. Tripodi**
Journal of Thrombosis and Haemostasis
Volume 2 Issue 11 Page 1946
Blackwell Synergy
On behalf of the Subcommittee on Control of Anticoagulation of the Scientific and Standardization Committee of the ISTHHemostasis and Thrombosis Research Center, Department of Hematology, Leiden University Medical Center, Leiden, the Netherlands; *Division of Hematology, National Institute for Biological Standards and Control, Potters Bar, UK; Service Central d'Immuno-H?matologie, H?pital Ambroise Par?, Boulogne, France; Department for Thrombosis Research, University of Southern Denmark and Department of Clinical Biochemistry, Ribe County Hospital, Esbjerg, Denmark; ?Hamilton Civic Hospitals Research Center, Hamilton, Ontario, Canada; ?ECAA Central Facility, School of Biological Sciences, The University of Manchester, Manchester, UK; and **A. Bianchi Bonomi Hemophilia and Thrombosis Center, IRCCS Maggiore Hospital, University of Milan, Milan, Italy
Summary. Reliable international normalized ratio (INR) determination depends on accurate values for international sensitivity index (ISI) and mean normal prothrombin time (MNPT). Local ISI calibration can be performed to obtain reliable INR. Alternatively, the laboratory may determine INR directly from a line relating local log(prothrombin time [PT]) to log(INR). This can be done by means of lyophilized or frozen plasmas to which certified values of PT or INR have been assigned. Currently there is one procedure for local calibration with certified plasmas which is a modification of the WHO method of ISI determination. In the other procedure, named 'direct' INR determination, certified plasmas are used to calculate a line relating log(PT) to log(INR). The number of certified plasmas for each procedure depends on the method of preparation and type of plasma. Lyophilization of plasma may induce variable effects on the INR, the magnitude of which depends on the type of thromboplastin used. Consequently, the manufacturer or supplier of certified plasmas must assign the values for different (reference) thromboplastins and validate the procedure for reliable ISI calibration or 'direct' INR determination. Certification of plasmas should be performed by at least three laboratories. Multiple values should be assigned if the differences between thromboplastin systems are greater than 10%. Testing of certified plasmas for ISI calibration may be performed in quadruplicate in the same working session. It is recommended to repeat the measurements on three sessions or days to control day-to-day variation. Testing of certified plasmas for 'direct' INR determination should be performed in at least three sessions or days. Correlation lines for ISI calibration and for 'direct' INR determination should be calculated by means of orthogonal regression. Quality assessment of the INR with certified plasmas should be performed regularly and should be repeated whenever there is a change in reagent batch or in instrument. Discrepant results obtained by users of certified plasmas should be reported to manufacturers or suppliers.

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