Intra-assay variation, an estimate of repeatability, was calculated in each participant center as the coefficient of variation of 20 to 30 measurements of the same analyte, performed consecutively during the same day: CV = 100xSD/mean. Interassay variation, a measure of reproducibility, was calculated in each participant center as the coefficient of variation of 20 to 30 measurements of the same analyte, performed consecutively over 20 to 30 days. The measurement bias, an estimate of accuracy, was calculated as 100x[(participant result) – (peer group target result)]/(peer group target result). Finally, the uncertainty of measurement, an estimate of precision, was calculated as √ [u²(IQA) + u² (IQA)], with u2(IQA) denoting the variance (square SD) of all IQA results of the same concentration level, and u2(EQA) denoting the variance of corresponding EQA results. Outliers were not excluded from the presented data. The intra-assay and interassay sample size (n) denotes the number of studies (20-30 measurements each) performed by the participants, while the bias and UM sample size refers to the number of individual results obtained by the participants. CV, coefficient of variation; EQA, external quality assurance; IQA, internal quality assurance; SD, standard deviation; UM, uncertainty of measurement. Special symbols denote the origin of 200-2019 recommendations: ^* manufacturer (Thermo Fisher Scientific), ^** CLSI 2009 (reference 9),^*** CLSI 2016 (reference 7), ^§ SFBC (French Society for Clinical Biology) 1999, ^# UK NEQAS (UK National External Quality Assessment Services) 2019,^¤ AFSSAPS (French Agency for Health Security) 2010.