Competitive binding techniques such as radioimmunoassay (RIA) are widely
used to measure an enormous variety of compounds in biological fluids.
Current methods have 1 2 arisen from the pioneering work ofYalow and
Berson in the U. S. A. and Ekins in the u. K. Much of the early
development was concerned with the analysis of protein hormones, and
nearly a decade passed before attention focussed also on small molecules
such as steroids and drugs. The potential of immunoassay methods for
drug monitoring in clinical and forensic laboratories and in addict
treatment programmes resulted in the commercial production of
immunoassays for various therapeutic and abused drugs, making the
technique available to laboratories lacking the facilities to raise
their own antisera and synthesise labelled compounds. However,
commercial assays are not only expensive but are restricted in range,
and so it is advantageous for a forensic laboratory to have the
capability to devise "in-house" immunoassays suited to its particular
requirements. This chapter describes the theory and practice of RIA in
forensic drug analysis. Much of the theory and some of the practice are
applicable to immunoassays in which non- isotopic labels are used, but
such assays are not described in detail since, to date, the versatility
and sensitivity of RIA have made it the immunoassay technique of choice
in forensic toxicology. The particular advantages of RIA are its
sensitivity and the fact that samples such as haemolysed blood can be
assayed with little or no prior preparation.