The role of External Quality Assessment Schemes in monitoring and improving the standardization process.

This paper examines the evolution of External Quality Assessment Schemes (EQAS), focusing on the need for target values based on reference methods and control material commutability. Although the key role of EQAS in the standardization process has been clear from the start, it has never been totally implemented, mainly due to the lack of commutable materials. Costs, the difficulty to assign reference method values, and the non-availability of field methods able to provide results traceable to the reference measurement system have also played an important role. Using commutable materials with target values assigned by reference methods, EQAS can define and verify the uncertainty of test results produced by analytical methods. EQAS may also improve standardization, proposing rules for the post-analytical phase (uniform units of measurement, description of measurands, rounding off and number of decimal places to report). Only the described EQAS may become a reliable indicator of the status of the standardization process. Improvements will only take place if stakeholders (governments and international organizations, scientific societies, manufacturers and specialists in laboratory medicine) act in a coordinated way to take corrective action every time EQAS clearly indicates a suboptimal situation.