Radioimmunoassay

RADIOIMMUNOASSAY

INTRODUCTION

The introduction of radioimmunoassay (RIA) and its subsequent development as a possible versatile tool in wide spheres of science, occurred empirically to the initiators. Radioimmunoassay was primarily developed by Berson and Yalow* (1959) for the quantitative measurement of insulin in human plasma, which eventually not only revolutionized endocrinilogy as such but also paved the way for the clinical chemistry laboratory practice in general. As on date RIA principles have found wide application in the field of drug analysis, pharmacokinetic studies, drug-therapy monitoring and above all the immunodiagnosis in medicine to mention but a few. Specifically RIA measures the actual effect of changing concentrations of a particular substance present in a biological fluid (e.g., blood, plasma, urine) based on an in vitro system consisting of radioactive standards of the same substance and a specific antibody. In a true sense, RIA is nothing but an indirect method of analysis because it does not make use of either the radioactive standard or the antibody present in the original sample.

Before the emergence of radioimmunoassay as an acceptable analytical technique, a number of other methods were employed for the analysis of ‘drugs’ in the plasma. Prominent among these methods were thin layer chromatography (TLC), gas-liquid chromatography (GLC), spectrofluometry (SPF) and ordinary radiolabelling assay. The above methods, undoubtedly, have certain advantages to their credit ; however, the disadvantages outnumbered the advantages, as stated below :

Disadvantages

·              Non-specificity of the technique,

·              Non-sensitivity of the method,

·              Involvement of the processes of extraction, purification and concentration of the specimen under investigation,

·              Heat treatment of the specimen resulted invariably in degradation and destruction of the substances, and

·              Many processes involved ultimately make the analysis rigorous and unnecessarily sluggish.

On the contrary, RIA provided a specific, sensitive, rapid, convenient, reliable, reproducible and less expensive assay methods for biological fluids.

The introduction of enzyme immunoassay (EIA) and similar allied immunoassay techniques in early eighties showed, in fact, a brighter path towards quantitative analysis.

RIA technique has splendidly made available to the drug analyst, endocrinologist, physiologist, phar-macologist, clinical chemist and biochemist a very sensitive, specific and comparatively easier method for the quantitative measurement of serum or plasma drug, hormones, enzyme concentrations, besides, drug concen-trations in biological fluids. It has also proved to be equally important in pharmacokinetic studies and in acute monitoring of patient drug therapy according to Mule et al* (1974).

Skelley et al** (1973) listed a number of substances that may be determined quantitatively by the help of the RIA method, namely : nucleic acids, proteins, enzymes, prostaglandins, steroidal hormones, anti-bodies, cancer and viral antigens, vitamins, and drugs together with their respective metabolites.

Importantly, the pioneer work or Oliver and coworkers*** (1968) and followed by valuable and mean-ingful contributions by Landon and Moffat**** (1976) proved beyond any reasonable doubt the efficacy of RIA in the quantification of a host of pharmaceutical substances.