To Perform Radioimmunoassay
37
Radioimmunoassay (RIA) is a highly sensitive and specific analytical tool used for
detection of antigen or antibody in a sample. It was developed in the late 1950s by
Rosalyn Yalow and Solomon A. Berson for estimation of insulin in human serum.
37.1 Principle........................................
Radioimmunoassay combines the principles of radioactivity of isotopes and immu-
nological reactions of antigen and antibody. The principle is based on the competi-
tion between labelled and unlabelled antigens to bind with antibody to form antigen-
antibody complexes. The test is employed to determine the concentration of
unlabelled antigens. The antibody specific for antigen is incubated with unlabelled
antigen in the presence of high concentration of antigens labelled with isotope (say I
(^131) ). The presence of both labelled and unlabelled antigens in the sample mixture
creates a competition between these antigens to bind with antibody. Initially labelled
antigens will bind in more amounts due to their high concentration present in sample.
Then amount of unlabelled antigen is increased progressively in the sample. As the
concentration of unlabelled antigens increases, they will replace the labelled antigens
from their already existing antigen-antibody complex. Thus, the concentration of
labelled antigens bound with antibody will be inversely related to unlabelled
antigens, i.e., the higher is the concentration of labeled antigens bound with anti-
body, the less is the concentration of unlabelled antigens or vice versa. The concen-
tration of labelled antigen can be determined by precipitating them and determining
radioactivity present in this antigen-antibody complex. A standard curve is drawn
using different concentrations of unlabelled antigens and same quantities of antibody
and labelled antigens. From this plot the amount of unlabelled antigens present in the
test sample may be determined precisely (Fig.37.1).
#Springer Nature Singapore Pte Ltd. 2018
V. Kumar, K. D. Gill,Basic Concepts in Clinical Biochemistry: A Practical Guide,
https://doi.org/10.1007/978-981-10-8186-6_37
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