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International Collaborative Study for the Calibration of a Proposed International Standard for thromboplastin, human, plain

2010; Elsevier BV; Volume: 8; Issue: 9 Linguagem: Inglês

10.1111/j.1538-7836.2010.03980.x

1538-7933

Armando Tripodi, Veena Chantarangkul, A M H P van den Besselaar, E. Witteveen, A. R. Hubbard,

Pharmaceutical Economics and Policy

According to the recommendation issued by the World Health Organization (WHO), working thromboplastins used in the prothrombin time (PT) test for the laboratory control of oral anticoagulant treatment must be calibrated against International Standards (IS) to determine the International Sensitivity Index (ISI) necessary to convert PT results into International Normalized Ratio (INR) [1WHO Expert Committee on Biological StandardizationGuidelines for thromboplastins and plasma used to control oral anticoagulant therapy.World Health Organ Tech Rep Ser. 1999; 889: 64-93Google Scholar]. Two preparations of human thromboplastin, provisionally coded 07/314 and 08/144, were proposed as candidates for the WHO IS for thromboplastin (human, plain), meant to replace the IS coded rTF/95 (human, plain) whose stocks are nearly exhausted. The preparations made of relipidated human recombinant tissue factor were submitted and calibrated in an international collaborative study organized and carried out under the auspices of the Scientific and Standardization Committee of the International Society on Thrombosis and Haemostasis. The study involved 21 expert laboratories from 13 countries and the calibration was performed after a common protocol against the existing WHO ISs (i.e. rTF/95 and RBT/05). The ISI values for both candidates were estimated according to WHO guidelines [1WHO Expert Committee on Biological StandardizationGuidelines for thromboplastins and plasma used to control oral anticoagulant therapy.World Health Organ Tech Rep Ser. 1999; 889: 64-93Google Scholar]. Exclusion of non‐therapeutic patient samples and outliers was performed as described recently [2Van Den Besselaar A.M.H.P. Chantarangkul V. Tripodi A. Effect of prothrombin time outlier exclusion rules on ISI calibration in multicentre studies.Thromb Res. 2010; 125: 523-8Abstract Full Text Full Text PDF PubMed Scopus (2) Google Scholar]. As for the previous collaborative studies [3Tripodi A. Chantarangkul V. Negri B. Clerici M. Mannucci P.M. International collaborative study for the calibration of a proposed reference preparation for thromboplastin, human recombinant, plain. On behalf of the Subcommittee on Control of Anticoagulation.Thromb Haemost. 1998; 79: 439-43Crossref PubMed Scopus (52) Google Scholar, 4Chantarangkul V. Van Den Besselaar A.M.H.P. Witteveen E. Tripodi A. International Collaborative Study for the Calibration of a Proposed International Standard for Thromboplastin, Rabbit, Plain.J Thromb Haemost. 2006; 4: 1339-45Crossref PubMed Scopus (24) Google Scholar] the two candidates were compared based on predetermined criteria, which included (i) the within‐laboratory imprecision of calibration, assessed as the coefficient of variation (CV) for the estimation of the slope of the relationship between log‐transformed PT values of fresh plasmas from 20 healthy subjects and 60 patients stabilized on oral anticoagulants, which were tested by means of the manual (tilt‐tube) technique with the candidates and each of the ISs; (ii) the between‐laboratory imprecision of the calibration, assessed as the CV of the ISI and (iii) the conformity to the calibration model, assessed as the percentage of calibrations with important deviations of normals from patients' line as assessed according to the WHO guidelines [1WHO Expert Committee on Biological StandardizationGuidelines for thromboplastins and plasma used to control oral anticoagulant therapy.World Health Organ Tech Rep Ser. 1999; 889: 64-93Google Scholar]. A deviation was regarded important if INRs calculated with the ISI derived from the overall regression line (i.e. for patients plus healthy subjects) differed by more than 10%, in the INR range 2–4.5, from INRs calculated with the equation describing the regression line for patients only [1WHO Expert Committee on Biological StandardizationGuidelines for thromboplastins and plasma used to control oral anticoagulant therapy.World Health Organ Tech Rep Ser. 1999; 889: 64-93Google Scholar]. Stability of the candidates was assessed through an accelerated degradation study after storage of ampoules at various temperatures (+4, +30, +37, +45 °C) for different time intervals as previously reported [5Van Den Besselaar A.M.H.P. Van Rijn C.J.J. Taberner D.A. Goodman L.J. Poller L. Clarke K. Heat stability of two candidate international reference preparations for recombinant human tissue factor.Thromb Haemost. 1997; 78: 852-4Crossref PubMed Scopus (4) Google Scholar]. Twenty out of 21 participants submitted data for statistical analysis. Within‐laboratory imprecision of the calibration (expressed as the CV value of the slope) was below 3% in 87.5% of the cases for 07/314 versus 92.5% for 08/144 (Table 1). The mean ISI value of the candidate 07/314 calibrated against the two existing ISs was 1.084 and the between‐laboratory CV of the ISI was 5.7%. The corresponding values for the candidate 08/144 were 1.082 and 4.2%. Finally, the percentages of calibrations with important deviations of normals from patients line were 20% and 8.75% for 07/314 and 08/144. For both candidates, storage at 30 °C or higher did slightly affect the ISI value. No significant change, however, was observed after storage at 4 °C for 150 days, suggesting that both preparations display suitable stability when stored at −20 °C.Table 1ISI assignment and comparative performance of the candidatesISI assignment to candidatesInternational Standard (IS)Number of calibrationsMean ISIBetween‐lab SDBetween‐lab CVStandard error of mean ISICandidate 07/314rTF/95201.0730.0504.6RBT/05201.0950.0716.5Overall Calibration401.084*5.70.0097Candidate 08/144rTF/95201.0700.0383.5RBT/05201.0950.0504.6Overall Calibration401.082*4.20.0072Comparative performance of the candidatesCandidateWithin‐lab imprecision of the CalibrationBetween‐lab imprecision of the CalibrationInadequacy of the WHO model% of Calibrations with CV of the slope <3%†CV (%) of the ISI‡Numbers (%) of Calibrations with important deviations from the adequacy of the WHO model in the INR range 2–4.5‡INR 2.0INR 4.5INR 2.0 plus INR 4.507/31487.55.712 (30)4 (10)16 (20)08/14492.54.25 (12.5)2 (5.0)7 (8.75)*Mean of ISI values obtained with two different IS. No outlying ISI values were detected. †the higher the better. ‡the lower the better. Open table in a new tab *Mean of ISI values obtained with two different IS. No outlying ISI values were detected. †the higher the better. ‡the lower the better. The candidate 08/144 gave the lowest within‐laboratory variation of the slope and the lowest between‐laboratory variation of the ISI, as well as the lowest number of calibrations with important deviations from the WHO calibration model. It was therefore proposed that the preparation coded 08/144 be submitted to WHO as the 4th International Standard for Thromboplastin, human, recombinant, plain, with an assigned ISI value of 1.082. The preparation has been recently accepted by WHO and coded as rTF/09. The authors state that they have no conflict of interest. We wish to thank all participants of the international collaborative study for their contribution and the ISTH/SSC Subcommittee on Control of Anticoagulation for their support. We further acknowledge the following contributions: 1Provision of candidates (in alphabetic order)Instrumentation Laboratory (Orangeburg, NY)Siemens Healthcare Diagnostics Products GmbH (Marburg, Germany)2Provision of Control PlasmasSiemens Healthcare Diagnostics Products GmbH (Marburg, Germany)3Provision of blood collection systemsW. Slachmuylders, (Sarstedt B.V., Etten‐Leur, The Netherlands)4Filling and Coding of CandidatesNational Institute for Biological Standards and Control (Potters Bar, UK) and Instrumentation Laboratory (Orangeburg, NY)5Assembly and Shipment of the MaterialE. Witteveen and K. Imthorn (Leiden, the Netherlands)6SponsorsDiagnostica Stago, HemoSense, International Technidyne Corporation, Roche Diagnostics, Siemens Healthcare Diagnostics, Instrumentation Laboratory. Participants (in alphabetical order) of the international collaborative study. 1P. Angchaisuksiri/K. Arurachai. Division of Hematology, Department of Medicine, Ramathibodi Hospital, Mahidol University, Bangkok, Thailand.2I. Bodo. Department of Hematology and Stem Cell Transplantation. St. László Hospital Budapest, Hungary.3V. Chantarangkul/A. Tripodi. Hemophilia and Thrombosis Center Angelo Bianchi Bonomi, Department of Internal Medicine, University and IRCCS Ospedale Maggiore Policlinico, Mangiagalli e Regina Elena Foundation, Milan, Italy.4T. Gago. Serviço Patologia Clínica, Hospital de Santa Cruz, Carnaxide, Portugal.5M. Johnston. Hemostasis Reference Laboratory, Henderson Research Centre, Hamilton, Canada.6K. Kynde. Department of Clinical Biochemistry, Roskilde University Hospital, Denmark.7S. Kitchen. Dept of Coagulation, Sheffield Haemophilia and Thrombosis Centre, Royal Hallamshire Hospital, Sheffield, UK.8L. Ippolito/G. Bianchi. U.O. Diagnostica Emato‐chimica, Dipartimento di Patologia e Medicina di Laboratorio, Azienda Ospedaliero‐Universitaria di Parma, Parma, Italy.9C. Legnani. U.O. Angiologia e Malattie della Coagulazione "Marino Golinelli", Azienda Ospedaliero‐Universitaria di Bologna, Policlinico S. Orsola ‐ Malpighi, Bologna, Italy.10T. Lindahl. Department of Clinical Chemistry, University Hospital, Linköping, Sweden.11R. Manning. Laboratory of Haematology, Department of Coagulation, Hammersmith Pathology Centre, Hammersmith Hospital, London, UK.12M. Martinuzzo. Hematología, Laboratorio de Hemostasia y Trombosis, Fundación Favaloro, Buenos Aires, Argentina.13D. Mezzano. Laboratorio de Hemostasia y Trombosis, Escuela de Medicina, Univ. Católica de Chile, Santiago, Chile.14N. Opartkiattikul. Department of Clinical Pathology, Faculty of Medicine, Siriraj Hospital, Bangkok, Thailand.15K. Overgaard/J. Jespersen. Department of Clinical Biochemistry, Hospital of South West Denmark, Esbjerg, Denmark.16V. Pengo/E. Bison. Ospedale Ex‐Busonera, Servizio di Prevenzione e Terapia della Trombosi‐Cardiologia, Università di Padova, Padova, Italy.17W. Plesch. Roche Diagnostics, Mannheim, Germany.18R. Redaelli. Laboratorio Emostasi e Trombosi, Divisione di Ematologia Talamona, Ospedale Niguarda Cà Granda, Milano, Italy19S. Reed. Thame Thrombosis and Haemostasis Research Foundation, Thame, Oxon, UK.20A.M.H.P. van den Besselaar/E. Witteveen, Department of Thrombosis and Hemostasis, Leiden University Medical Center, Leiden, the Netherlands