While immunoassays are now used in a variety of fields including medical, food technology
and environmental protection because of their high sensitivity, high specificity and ease of automation
to provide highly cost effective analyses, it has been in medical testing that their standardization has
been most intensely developed. The use of internationally agreed clinical protocols, common reference
intervals or decision limits and even electronic health records across health-care institutions are all
dependent on medical testing laboratories performing assays that are traceable to internationally
recognized reference measurement systems. The application of metrological principles to achieve
traceability and standardization for immunoassays is being pursued to this end. Comprehensive
measurement systems are available for the total serum hapten assays currently measured in the clinical
laboratory by immunoassay. Current research is investigating the usefulness of developing defined
systems for the measurement of non-bound fractions or "free" hormone levels of these types of
analytes. One strategy that has been successfully applied for the standardization of assays for large
molecular weight polypeptide measurands has been to localise the biological activity to a small
molecular weight moiety of the meausurand and to establish a reference measurement procedure for this
moiety as a surrogate for the total molecule of clinical interest. The standardization or harmonization of
assays for heterogeneous polypeptide hormones is also is another area of current research for
standardization of clinical immunoassays. The accreditation of medical testing laboratories to
ISO15189 standard requires that all testing methods including immunoassays are validated or verified
to be fit for purpose including the accuracy of the assay and the estimation of measurement uncertainty
as assessed by traceability to certified reference materials through a documented unbroken chain of
calibrations.
Keywords: Antibodies, Immunoassays, Standardization
