EQA SCHEME FOR IMMUNOASSAY: EVALUATION OF LABORATORY PERFORMACE THROUGH A SCORING SYSTEM

To evaluate the analytical performance of laboratory and methods commercialy available for immunoassay, we organized an EQA for hormones, tumor markers and other biochemical markers. The EQA scheme is carried out by QualiMedLab, a spin-off company established in the Institute of Clinical Physiology of the Italian National Research Council (IFC-CNR). In the EQA scheme laboratories involved receive and measure 18 control samples distributed in 6 surveys for year. Control samples are sent by mail to laboratories. On the web site http://eqas.ifc.cnr.it are reserved personal web pages in which each laboratory can insert directly its own results obtained assaying control samples. Through an internal web site, QualiMedLab staff can manage and treat laboratory data, examine anomalous results and perform statistical analysis. Target value for each method is the mean of all measurements made with the same method. The imprecision of measurement (CV%) of most of analytes considered in our EQA schemes has significantly decreased in the last 10 years. The improvement is due to the evolution of technology in laboratories' instrumentation as well as the diffusion of EQA schemes, that encourage laboratories to achieve continuous quality improvements. Actually, in a few days, laboratories can download reports in PDF format containing the evaluation of their results and the main statistics. Further statistical information can also be examined through dynamic web pages. To allow participants an easy evaluation of their own analytical performance, the following scoring system has been adopted; each result is scored according to its deviation from target value (method mean) expressed in SD units (Z-score): dev% = (result-target value)/(target value)% Z-score is computed as the ratio of percent deviation from target and "state-of-the-art" imprecision: Z = (dev%)/(CV% "state-of-the-art") "State-of-the-art" imprecision is computed as mean imprecision of the methods most used in the survey. In figure 1 are reported laboratory scores. To take account that the "state-of-the-art" imprecision depends on the analyte concentration, 3 CVs are computed corresponding to 3 concentration range (low, medium and high concentrations). CV "state-of-the-art" is updated every year on the bases of the results collected in the last year. The imprecision of measurement (CV%) of most of analytes considered in our EQA schemes has significantly decreased in the last 10 years. The improvement is due to the evolution of technology in laboratories' instrumentation as well as the diffusion of EQA schemes, that encourage laboratories to achieve continuous quality improvements.