External quality assessment of hormone determinations

Hormone determinations are of central importance to the practice of Clinical Endocrinology, and ensuring their correct use and performance is a multidisciplinary responsibility involving clinicians, laboratory staff, manufacturers of diagnostic systems and healthcare regulatory agencies. All these professional groups have, therefore, an interest in external quality assessment (EQA) as an audit tool that can identify areas where use of tests in routine practice requires improvement to reduce risks to patients. This chapter reviews the principles of EQA, and outlines its strengths and limitations, illustrated with example data from the UK National External Quality Assessment Service (UK NEQAS). The immunological nature of many hormone assays, often further complicated by heterogeneity of analyte structure and lack of suitable calibrators, presents special problems for the designers of EQA schemes in ensuring that specimens are appropriate and that target values are accurate. Laboratory users of EQA should have sufficient knowledge of the characteristics of the EQA schemes in which they participate to make informed interpretation of their data. The trend since the 1980s for in-house assays designed in individual laboratories to be superseded by automated assays provided by a small number of diagnostics manufacturers places a special responsibility on manufacturers to ensure reliable assay design and calibration. In collaboration with other parties EQA can help identify priorities for improved assay design and calibration. Although traditionally the focus of EQA has been on assessing the analytical phase it can also make some assessment of other important aspects of performance, e.g. the consistency of reference ranges and how results are interpreted. Overall, EQA has a valuable role both in laboratory accreditation and as an educational resource, thereby helping to ensure and improve the quality of laboratory services that support patient care.