Estimation of the uncertainty of CRMs in accordance with GUM: Application to the certification of four enzyme CRMs

Uncertainties of four enzyme-CRMs that have recently been certified in a co -operation between the IRMM and the International Federation for Clinical C hemistry were estimated. Estimation was based on the sum of the uncertainti es of characterization, homogeneity and stability. Data from the certificat ion collaborative study were used to estimate laboratory uncertainties, whi ch form the basis for the uncertainty of characterization. Estimations for the uncertainty of homogeneity were derived from classical homogeneity stud ies. The estimations of uncertainty of stability caused the most difficulti es. Realistic uncertainties fitting the needs of customers while being deri ved from measurement data based on theoretical considerations were obtained .