Dr AMHP van den Besselaar has been an active member of the European Concerted Action on Anticoagulation and European Action on Anticoagulation since its inception and made important contributions. Present minor disagreements should not therefore be regarded as fundamental differences.
He slightly misquotes one report in which he was a co-author  in his reply to our ‘rebuttal’ . It did not entail just one combination of brain thromboplastin and human recombinant reagent but two different reference thromboplastins, human and rabbit, with ISI established at ECAA national laboratories. Different numbered sets of ECAA plasmas were also tested at 121 participant centres. They were also supplied together with five coumarin plasmas to 45 centres employing human reagents and 76 employing rabbit reagents giving good INR results.
We did not ‘suggest’  that certified prothrombin time values for freeze-dried plasmas cannot be used for ISI calibration of dissimilar thromboplastins but our report clearly stated they ‘cannot be used’.
The reliability of the ECAA plasma sets in quantifying the warfarin-induced coagulation defect was described in a series of international studies including over 100 laboratories worldwide.
Dr van den Besselaar is correct in stating his presentation was in 2007 not 2006. We apologise for this slight error of dating his lecture slides stored in our computer.
Whether artificially depleted plasmas can always reliably mimic natural coumarin plasmas, has been a constant concern of the ECAA. We believe we have defined this relationship and that although there were some measurable differences with some commercial thromboplastins, they are of less clinical importance with modern reagents. Thromboplastins require calibration therefore by at least the relevant human and rabbit independent calibration routes. Bovine origin reagents are also still used in clinical practice so the ECAA Calibrants continue to be certified by the three different routes.
We trust this clarifies the minor points of disagreement.