International collaborative study for the calibration of a proposed World Health Organization International Standard for thromboplastin, human, recombinant: a report from the International Federation of Clinical Chemistry and Laboratory Medicine (IFCC)-Scientific and Standardization Committee (SSC)/ISTH working group on prothrombin time/international normalized ratio standardization.

Authors

Michelle P van der Helm, Claudia J J van Rijn, Shanti S Baktawar, Charmane F Abdoel, Steve Kitchen, Michelle Bryant, Paula Brown, Armando Tripodi, Erica Scalambrino, Marigrazia Clerici, Petra Herbel, Anja Jünschke, Piet Meijer, Anne Stavelin, Craig Thelwell, Christa M Cobbaert, Antonius M H P van den Besselaar

Published in

Research and practice in thrombosis and haemostasis. Volume 10. Issue 4. Pages 106793. Epub Jun 12, 2026.

Abstract

The availability of International Reference Preparations for thromboplastins, later on referred to as International Standards (ISs) for thromboplastins is essential for calibration of prothrombin time (PT) measurement systems and for the international normalized ratio (INR). It is proposed to replace the current fifth IS for thromboplastin, human, recombinant (coded rTF/16) and the fifth IS for thromboplastin, rabbit, plain (coded RBT/16) by a single IS for defining a reference measurement system for PT/INR tests, in agreement with the concept of metrological traceability.
This study aimed to determine the international sensitivity index (ISI) for the proposed sixth IS for thromboplastin, human, recombinant (coded 24/114).
An international collaborative study was carried out for the assignment of the ISI to the proposed IS by calibration against the current fifth IS for thromboplastin, human, recombinant. PT measurements were performed by 8 trained operators in 4 laboratories (2 operators in each laboratory) using the harmonized manual tilt tube technique. The World Health Organization calibration procedure was followed.
ISI values from 8 operators varied from 1.04 to 1.12, and the mean ISI for the proposed IS coded 24/114 was 1.08 (between-operator coefficient of variation, 2.8%).
The material coded 24/114 has been accepted by the World Health Organization as the sixth IS for thromboplastin, human, recombinant. Extensive prior training and external quality assessment surveys for the operators reduced the between-operator coefficient of variation. In this era of metrological traceability, a sustainable reference measurement system has been developed for PT/INR based on the harmonized manual tilt tube technique and a new IS.

PMID:
42472241
Bibliographic data and abstract were imported from PubMed on 19 Jul 2026.

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