Basic features of biomedical assays

All biomedical assays have certain aspects in common, the most striking of which is that they generally involve protein-binding. Ligand-ligator interactions and the resulting response form the basis of most assays. This paper reviews the advantages and limitations of different types of assays ranging from long-term bioassays to in vitro assays using cell-free components. Consideration of these aspects helps in the understanding of the different assays, selection of appropriate assays for different applications, and the better interpretation of assay results. Clinical chemists, hematologists, endocrinologists, immunologists, and scientists from other disciplines have each developed their own measurement methods and units. This paper seeks to identify those aspects and principles common to assays in all such disciplines, concentrating on protein-binding systems. Understanding what and how different assays measure may clarify why different assay methods often give different results.