Certified reference methods and certified reference materials for realisation of traceability in measuring serum glucose, cholesterol, creatinine, total protein and albumin are available. If the values of working calibrators are traceable to these reference methods and materials then comparable results of routine measurements should be obtained – different calibrators are harmonised. Harmonisation of calibrators is considered a strong tool for comparability improvement at least to the level of quality requirements defined as medical needs. We used four calibrators from three manufacturers for calibration of measurement systems Roche Modular-Abbott (two concentration levels), Roche, Olympus and studied the level of their harmonisation. Large systematic differences, larger than medical requirements were found in cholesterol, creatinine, total protein and albumin measure - ments. The highest systematic differences were found for total protein and albumin measurements but significant differences were even detected in cholesterol estimations, where traceability can be easily realised by a well established international reference system. Differences between calibrators Roche and Olympus were lower than between calibrators Abbott and the others. In many cases even maximal differences were obtained between two Abbott calibrators despite of their identical origin. The conclusion from results of this study is that traceability realisation is either not well done or is not effective. Harmonisation between tested calibrators is often very low and these calibrators cannot be used out the framework of individual homogenous routine measurement systems. On the other hand results of external quality assessment show much better interlaboratory comparability than could be expected from observed low calibrators harmonisation. It means that results reached by laboratories in external quality assessment do not reflect the real level of traceability.

        Key words: traceability, working calibrators, systematic differences, harmonisation, medical needs.