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Chapter 3 : Protein Analysis for Diagnostic Applications
In the context of the amazingly diverse and dynamic array of proteins in the human proteome, a relatively tiny set of proteins representing a few hundred gene products are analyzed for diagnostic purposes. Applications of mass spectrometry to analysis of plasma peptide components over the last few years suggest that there are a large number of potential diagnostic markers among these components. Further description of analysis of proteins by two-dimensional electrophoresis and peptides by mass spectrometry is present in this chapter, which describes research and potential future clinical laboratory methods. Potential types of diagnostic specimens are summarized in this chapter. Blood represents the most common specimen collected for protein analysis. There are a variety of different types of diagnostic questions that are addressed by protein analysis. The simplest is the qualitative question of whether a protein serving as a physiological marker is present or absent in a particular specimen. Binding assays represent the broadest range of functional assays for proteins in the clinical laboratory. Clinical laboratories have applied a variety of electrophoretic, chromatographic, and other separation techniques to analysis of proteins. These techniques are useful for qualitative analysis of the size, charge, associations, and other physical properties of proteins that may not be distinguished by quantitative methods such as immunoassays or functional assays. The electrophoretic method provides higher resolution than the typical methods for serum protein analysis, and it is applied in the clinical laboratory to achieve higher-resolution separations of immunoglobulins for evaluation of oligoclonal bands in cerebrospinal fluid.
Immunoprecipitin curve. At a fixed concentration of antibody, the type of antigen-antibody complex that forms is dependent upon the antigen concentration.
Diagram of an antigen excess-type assay using a solid support to immobilize the antibody.
Diagram of a two-site antibody excess-type immunometric (labeled-antibody) assay.
Types of specimens for diagnostic evaluation of proteins
Factors affecting specimen collection
Factors in selection of an immunoassay