Traceability to a common standard for protein measurements by immunoassay for in-vitro diagnostic purposes.

Background: There is a lot of confusion about the meaning of "measuring a protein in biological fluids" for in-vitro diagnostic purposes. This is due to a lack of understanding of metrological concepts and of acceptance of a pragmatic metrological concept for mixture analysis.

Methods: We describe the metrological concepts that apply to measurement of proteins. We propose a pragmatic reference measurement system for protein analysis. We investigate the feasibility of the approach with TSH as example.

Results: The reference measurement system for a protein should be viewed as a dynamic continuum from discovery to translation into an SI-component. A quasi surrogate component-mixture may be defined by recommendations for epitopes that immunoassays should recognize. The all-procedure trimmed mean is proposed as surrogate reference measurement procedure. Traceability is established by transfer of the IU of an WHO standard to a panel of commutable sera. Investigation of the TSH-example showed that the approach may be feasible.

Conclusions: The proposed pragmatic concept would be a major step towards traceability of protein measurements by immunoassay. It would allow a staged introduction of standardization during the continuum from discovery of a protein to full scientific understanding and transformation to the SI-unit.