Sources and performance criteria of uncertainty of reference measurement procedures

Objective: This article wants to focus on the today available Reference Measurement Procedures (RMPs) for the determination of various analytes in Laboratory Medicine and the possible tools to evaluate their performance in the laboratories who are currently using them.

Methods: A brief review on the RMPs has been performed by investigating the Joint Committee for Traceability in Laboratory Medicine (JCTLM) database. In order to evaluate their performances, we have checked the organization of three international ring trials, i.e. those regularly performed by the IFCC External Quality assessment scheme for Reference Laboratories in Laboratory Medicine (RELA), by the Center for Disease Control and Prevention (CDC) cholesterol network and by the IFCC Network for HbA_1c.

Results: Several RMPs are available through the JCTLM database, but the best way to collect information about the RMPs and their uncertainties is to look at the reference measurement service providers (RMS). This part of the database and the background on how to listed in the database is very helpful for the assessment of expanded uncertainty (MU) and performance in general of RMPs. Worldwide, 17 RMS are listed in the database, and for most of the measurands more than one RMS is able to run the relative RMPs, with similar expanded uncertainties. As an example, for a-amylase, 4 SP offer their services with MU between 1.6 and 3.3%. In other cases (such as total cholesterol, the U may span over a broader range, i.e. from 0.02 to 3.6%). With regard to the performance evaluation, the approach is often heterogenous, and it is difficult to compare the performance of laboratories running the same RMP for the same measurand if involved in more than one EQAS.

Conclusions: The reference measurement services have been created to help laboratory professionals and manufacturers to implement the correct metrological traceability, and the JCTLM database is the only correct way to retrieve all the necessary important information to this end.