Radioimmunoassay (RIA) : This method is used for the quantitation of antigens or haptens
that can be radioactively labeled. It is based on the competition for specific antibody between the la
beled (known) and the unlabeled (unknown) concentration of material. The complexes that forn be
tween the antigen and antibody can then be separated and the amount of radioactívity measured. The
more unlabeled antigen is present, the less radioactivity there is in the complex. The concentration of
the unknown (unlabeled) antigen or hapten is determincd by comparison with the effect of standards.
RIA is a highly sensitive method and is commonly used to assay hormones or drugs in serum. The
radioallergosorbent test (RAST) is a specialized RIA that is used to measure the amount of serum
lgE antibody which reacts with a known allergen (antigen).
Uses: RIA has many uses, including narcotics detection, blood bank screening for hepatitis (a highly contagious condition) virus, early cancer detection, measurement of growth hormone levels, tracking of the leukemia virus, diagnosis and treatment of peptic ulcers, and research with brain chemicals called neurotransmitters.
Which among the following radioactive isotope is commonly used in Radioimmunoassay?
a) Sulphur-35
b) Phosphorus -32
c) Iodine -125
d) Nitrogen -14
Answer: c) Iodine -125
