Structure, organisation and activities of an international reference system for cholesterol measurement are described. The details on the certification processes of the routine measurement systems and routine clinical laboratories are introduced including required precision and validity criteria. The cholesterol reference meas- urement laboratory network is described. The diagnostic decision limits for cholesterol (5 mmol/l in European guidelines and 5.17 mmol/l in USA guidelines) are interpreted by uncertainty of measurements derived from required precision (Ł 3,0 %) and validity (Ł 3,0 %). We also compared working calibrators Abbott, Roche and Olympus and estimated systematic differences between them. These differences are higher than demanded. It probably means that realisation of traceability in practice is not perfect. Also the results of inter-laboratory comparisons show that some routine laboratories are not able to fulfil required uncertainty of measurements. The number of such laboratories is probably significantly higher than apparent from results of external quality assessment tables. Uncertainty interpretation of diagnostic decision limits should respect positive or negative characteristic of their systematic differences due to their different influence on the diagnostics classification of risk for cardiovascular disease classification. Application of uncertainty in diagnostic laboratory examinations requires its another calculation than is proposed for others analytical laboratories. Standard procedure by using the estimation of individual standard deviations and by their followed combination is not suitable for this purpose.

        Key words: international reference measurement system of cholesterol, traceability, certification diagnostic decision limits, uncertainty.