Advancing excellence in laboratory medicine for better healthcare worldwide

Development of a Reference Measurement System for sustainable PT/INR Standardization (WG PT/INR)



Name Position Country Term Time in Office
C. Cobbaert Chair NL 1st 2021 04 - 2023 12
A. Cuker Member US    
S. Kitchen Member UK    
J. Meijers Member NL    
P. Meijer Member NL    
R. Niessen Member NL    
A. Stavelin Member NO    
A. Tripodi Member IT    
T. van den Besselaar  Member NL    
C. van Rijn Member NL    
F. Depasse Member/Corporate  FR    
Z. Cao  Corporate Rep./Instrumentation Lab. US    
C. Kung Corporate Rep./Instrumentation Lab. US    
S. Meyer dos Santos Corporate Rep./Roche Diagnostics DE    
N. Zander Corporate Rep./Siemens Healthineers DE    



Terms of Reference

  • To develop a harmonized reference measurement procedure based on the WHO manual tilt tube technique as well as the complete reference measurement system for global standardization of the PT/INR test. An entire reference measurement system is essential to anchor the International Standards for thromboplastin to assure longitudinal accuracy of PT/INR-test results in time and space.
  • To review the agreed WHO procedure for calculating ISI of new international standards as the procedure should not lead to deterioration of the traceability of PT/INR test results.
  • To evaluate the necessity of the co-existence respectively continuation of different thromboplastin reference materials for ensuring global PT/INR standardization.
  • To establish a network of at least three calibration labs running the harmonized MTT method for certifying the calibration of commercial thromboplastins from IVD-manufacturers.


Current Projects

  • Establishment of an entire Reference Measurement System for PT/INR standardization including a harmonized Reference Measurement Procedure based on the Manual Tilt Tube technique from WHO.
  • Establishment of one WHO International Standard for thromboplastin, replacing the current system in which two International Standards are coexisting. We suggest that the WHO International Standard might be recombinant human thromboplastin. This material should be stored at low temperature (-20 °C) and only be used for calibration of secondary standards. In this way the shelf life of the WHO International Standard is much longer than that of the present International Standards. The measurement uncertainty will be based on the between-laboratory imprecision of the national reference laboratories.
  • INR is defined by the International Sensitivity Index equation. In case a secondary standard does not comply with the ISI equation, a modified formula should be used (e.g. Tomenson’s correction).
  • Establishment of a Network of WHO reference laboratories, including at least three WHO reference laboratories. The reference laboratories should run the harmonized MTT and display their performance in EQA ring trials.
  • Establishment of a certification program for IVD-manufacturers (both for lab PT/INR tests and for POCT PT/INR tests) to ensure metrological traceability of PT/INR test results in time and space.
  • Preparation and certification of secondary reference materials for thromboplastin.
  • Long-term stability monitoring of WHO International Standard for thromboplastin.


List of Corresponding Members, nominated by Corporate Members

Name Corporate members
 Xiaoyong Shi MINDRAY 


Working Group Chair's contact

Prof. Christa COBBAERT
Head of Department Clinical Chemistry
and Laboratory Medicine LUMC
Afd. KCL
postroute E2-P
P.O. Box 9600
2300 RC Leiden
The Netherlands



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