ABSTRACT
A radiotracer was at the heart of the first reported immunoassay (Yalow and Berson, 1960), yet over 30 years later radioimmunoassay is still in widespread use and accounts for around 20 per cent of all publications in the field of immunoassay methods. Although initially surprising there are a number of good reasons for this. In many respects radiotracers still offer a number of significant advantages over the competition which, in the short term at least, are unlikely to be superceded. The most important of these is the fact that the measurement of the end point, i.e. radioactivity detection, is totally specific for the labelled tracer. This is in contrast to the position in fluoro-and enzymeimmunoassays where the samples themselves may contain background fluorescence or enzyme activity. The sensitivity of detection is also very good such that as little as 0.3 fmoles of labelled material can be reliably detected in one minute. Unlike chemiluminescent or enzymeimmunoassays the end point measurement in RIA can, if necessary, be repeated many times over.
