External quality assessment of immunoassays of peptide hormones and tumour markers: principles and practice

Abstract

External quality assessment schemes (EQAS) have traditionally emphasised the achievement of between-laboratory consensus. Although this is important, the application of EQAS to relatively new and evolving techniques such as immunoassay calls for a wider and more searching remit if the goals of accurate assays, properly used, are to be achieved. This article outlines the principles of EQAS for peptide hormones and tumour markers, emphasising key aspects such as validation of target values, dependency of results on sample type, and assessment of method characteristics such as vulnerability to interfering factors. The latter are considered to be important as they can affect patient care more seriously than modest degrees of imprecision or inaccuracy. EQAS play a unique role in providing objective data on assays performed in many laboratories under routine conditions and the data they provide can guide improvement in diagnostic reagents and laboratory practice.