Reference measurement systems in clinical chemistry.
BACKGROUND
In clinical chemistry, traceability of measurements is of high priority.


METHODS
In this literature review, current recommendations on the process of establishing traceability (or standardization) are critically discussed.


RESULTS
Traceability is to be established to the highest international standards by a comprehensive reference measurement system. Elementary to this system are a metrological basis, a measurement unit system, i.e., the Système International d'Unités (SI), its embodiment by a material standard and a calibration hierarchy for transfer of accuracy/trueness to the manufacturer's product calibrators and routine methods. However, for analytes lacking an unequivocally recognized entity, the International Unit (IU) and International Standard (IS) concept have been developed. On this basis, the review distinguishes between traceability of SI- and IU-analytes.


CONCLUSIONS
SI-traceability, exemplified by cortisol, is straightforward. However, special attention is needed for "free analytes" and "analyte families". For traceability of IU-analytes, exemplified by hCG, the standardization process passes different phases in function of the history of the analyte (discovery, ISs, measurement by bioassays/immunoassays, complete structure elucidation). However, perspectives to the development of an SI-based reference measurement system are realistic. Last but not least, for successful global implementation of the standardization process, consensus of all major players in the field will be required.
Laboratorium voor Analytische Chemie. Fac. Farmaceutische Wetenschappen, Universiteit Gent, Harelbekestraat 72, B-9000, Ghent, Belgium. linda.thienpont@rug.ac.be
Linda M
LM
Thienpont
Katleen
K
Van Uytfanghe
André P
AP
De Leenheer
D006063:Chorionic Gonadotropin / Q000032:analysis / Q000737:chemistry; D019963:Clinical Chemistry Tests / Q000379:methods* / Q000592:standards*; D004798:Enzymes / Q000378:metabolism; D006454:Hemoglobins / Q000032:analysis; D006801:Humans; D007394:International System of Units; D011786:Quality Control; D012015:Reference Standards; D014280:Triglycerides / Q000032:analysis
D006063:Chorionic Gonadotropin; D004798:Enzymes; D006454:Hemoglobins; D014280:Triglycerides