Discrepancy of the international normalized ratio observed in the external quality assessment survey: a cause for concern

Abstract

To cite this article: Tripodi A, Chantarangkul V, Legnani C, Frontoni R, Testa S. Discrepancy of the international normalized ratio observed in the external quality assessment survey: a cause for concern. J Thromb Haemost 2012; 10: 714-6.The External Quality Assessment (EQA) survey of the international normalized ratio (INR) organized and carried out by the FCSA (Italian Federation of Thrombosis Centers) enrols on average 240 participants across the country. Participants receive twice per year sets of lyophilized plasmas at increased levels of anticoagulation and are asked to determine the INR using their local methods (i.e. thromboplastin/ coagulometer combination). Participants also receive detailed instructions on how to handle lyophilized test plasmas (reconstitution and storage until analysis). Results are then centralized for statistical analyses that include the calculation for each test plasma of the following parameters. (i) The overall mean, after exclusion of outliers [1]; this value is taken as the ÔconsensusÕ value for further evaluation. (ii) The standard deviation (SD) and the coefficient of variation (CV). (iii) Results from each participant and plasma are compared with the ÔconsensusÕ value to calculate the deviation as percentage discrepancy ([participant value)consensus value]/consensus value) · 100 and z-score ([participant value)consensus value]/SD) · 100. Further analyses according to subgroups using the same thromboplastin in combination with coagulometers manufactured by the same company as the thromboplastins are performed whenever the numbers of participants in each subgroup are adequate. The lyophilized plasmas employed in the FCSA EQA survey and in this investigation were provided by Hart Biologicals (Hartlepool, UK). They were prepared from plasmas of patients stabilized on vitamin K antagonists (VKA). Factor V for these plasmas was higher than 70 IU dL (Table 1a) and most of the participants in this group had results that were far in excess of 20% from the ÔconsensusÕ value. Conversely, the mean INR obtained with the other thromboplastins used in the survey, whose number of participants exceeded 10, were in fair agreement with the INR ÔconsensusÕ value, with discrepancies that were 9% or less (i.e. )6% or )5% Recombiplastin [IL]; 8% or 7% Thromborel S [Siemens, Tarrytown, NY, USA]; 9% or 3% Innovin (Siemens); and 6% or 0% Thromboplastin S (Diagen, Oxford, UK) for plasmas B-1159-9 or B-1159-5, respectively). The discrepancy between the mean INR value obtained with Neoplastin Plus and the INR ÔconsensusÕ value sparked concern among participants in the survey and the thromboplastin manufacturer. Therefore, the organizers decided to carry out an independent investigation to seek explanations for the above discrepancy.To account for the possible inaccuracy of the international sensitivity index (ISI) determination declared by the manufacturer and used by participants in the survey, one lot of Neoplastin Plus (lot 624151), representative of the manufacturer production, was purchased and ...

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