A reference system for cortisol

Objectives: The International Federation of Clinical Chemistry (IFCC) initiated a pilot study, with cortisol as an example, that aims to implement the concept of standardization of hapten immunoprocedures on the basis of metrological traceability. In fact, this standardization concept comes down to correct calibration of measurement procedures, so that measurement results for patient samples can be traced back to the metrologically highest reference of a result, i.e., an SI unit as embodied in the primary reference material. In consequence, demonstration of standardization of a test system on the basis of traceability requires evaluation of measurement results pertaining to patient samples for accuracy. Such an evaluation shall be done by a correlation study of the routine test system with an accuracy-based reference measurement procedure. Design and methods: The IFCC project will select a panel of single donation human serum samples, and assign them with values for cortisol by measurement with at least two isotope dilution-gas chromatography/mass spectrometry reference methods. Limited amounts of the panel will be distributed to manufacturers, with the object to measure the samples with their calibrated immunoprocedures. The patient correlation studies between the routine and the reference methods will then be interpreted in terms of specificity and accuracy. It will also be investigated whether the performed comparison can be used as a basis for re-calibration. From the experience gained through this pilot study for cortisol, IFCC will formulate recommendations and guidance to manufacturers on how to perform and reliably interpret patient correlation studies. In this way, it is to be expected that the project might form a basis for general implementation of the concept of standardization of hapten immunoassays on the basis of metrological traceability.