Since 70 % of medical decisions are based on the results of laboratory analyzes, the basic goal of laboratory medicine is to obtain comparable results of patient sample measurements regardless of time, laboratory and measurement process. Comparability of the results regardless of time, laboratory and measurement process is achieved by establishing a traceability system to a common reference where the reference system plays an important role, and traceability is established by standardization or harmonization of the measurement process. Comparability between laboratories is checked through external quality assessment schemes (EQA), which allow the identification of analytical abnormalities and encourage improvements. We wanted to define the comparability of the results of Slovenian laboratories participating in the Slovenian National External Quality Scheme (SNEQAS). For assessment of 8 biochemical analytes (chlorides, glucose, iron, cholesterol, total bilirubin, AST, ALT, ALP) in 15 SNEQAS cycles, from 2014 to the third cycle in 2017, we used the sigmametric method and measurement uncertainty. The best results were obtained for iron and the worst results were obtained for chloride, glucose, cholesterol and ALP. There are several reasons for the incomparability of the results of Slovenian laboratories: noncommutability of the control samples of the SNEQAS scheme for the determination of biochemical parameters, the choice of statistical methods, equations and data (TEa, target value), traceability system to the common reference in laboratories is not established, the differences between reagents of different series, the laboratories use different analyzers, methods and reagents, systemic and random errors, and overall lack of standardization of measurement processes. Standardization should be started in individual laboratories an then continued in the SNEQAS scheme, using a commutable control material.
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