Clinical laboratory services strive to ensure that the right results are obtained in patients. Decisions on patient management are made on the basis of these results and the maintenance of high-quality output is essential. Precise and accurate results (by the processes of internal quality control (IQC) and external quality assessment (EQA)) and a timely and appropriate service (by means of a laboratory audit, clinical audit, laboratory accreditation and clinical governance) are generated by the delivery of a quality (defined as “a degree of excellence” in the Oxford English Dictionary) service in clinical immunology.

The major objective of quality assurance is to improve the quality of results for uniformity both within and between laboratories, so that an appropriate clinical interpretation can be made on the basis of that result. Within this objective, the role of IQC is to monitor the day-to-day precision and accuracy of a given assay. The role of EQA is broader in that it can compare and contrast different methods, thus also providing educational information.

The control of immunoassay systems can be especially challenging owing to the complexity of the methods used. Variability may be introduced at many levels, including the antigen source (whole tissue, cell extract, purified protein, recombinant protein), antibody detected (isotype, affinity, concentration), antibody detection system (polyclonal, monoclonal, affinity, conjugation (enzyme, fluorochrome) and methodological variations (incubation time, volume, choice of substrate). All these factors are taken into account when things go wrong.

This article suggests an approach to IQC, including the mathematical methods used to monitor precision and accuracy, appropriate reference materials and controls, and some internal checks that help in providing additional information.

Reference materials—the starting point for assured quality

Both IQC and EQA have underlying requirements for central reference materials (often incorrectly called standards) to enable direct comparisons to be made between laboratories. During the 1960s and 1970s, the …