New WHO–ADA recommendation for diagnosis of diabetes mellitus is described. The measurement of fasting plasma glucose (FPG) must be introduced for its application. This measurement requires optimisation of preanalytical processes described in the communication, reduce bias values close to zero and repeatability less than 1 %. The proposed interval between both cut-off values seems to be too narrow and should be conceived as the grey zone without diagnostic significance. Bias values derived from results of Czech inter-laboratory comparisons are inappropriately large and have a positive sign. This increases the da nger of false negative diagnostic classification. Evaluation of uncertainty in FPG measurement is demonstrated, conclusions for reorganisation of inter-laboratory comparisons are proposed. Interpretation of cut-off values assuming uncer- tainty is explained.

        Key words: diabetes diagnosis, WHO–ADA recommendation, fasting plasma glucose, optimisation of conditions, precision and bias of measurement.