Immunoradiometric assay (IRMA) is an

assay An assay is an investigative (analytic) procedure in laboratory medicine, mining, pharmacology, environmental biology and molecular biology for qualitatively assessing or quantitatively measuring the presence, amount, or functional activity ...

that uses

radiolabeled A radioactive tracer, radiotracer, or radioactive label is a synthetic derivative of a natural compound in which one or more atoms have been replaced by a radionuclide (a radioactive atom). By virtue of its radioactive decay, it can be used to exp ...

antibodies. It differs from conventional

radioimmunoassay A radioimmunoassay (RIA) is an immunoassay that uses radioactive tracer, radiolabeled molecules in a stepwise formation of immune complexes. A RIA is a very sensitive in vitro assay technique used to measure concentrations of substances, usually m ...

(RIA) in that the compound to be measured combines immediately with the radiolabeled antibodies, rather than displacing another

antigen In immunology, an antigen (Ag) is a molecule, moiety, foreign particulate matter, or an allergen, such as pollen, that can bind to a specific antibody or T-cell receptor. The presence of antigens in the body may trigger an immune response. ...

by degrees over some period. __TOC__ Principle:- A noncompetitive assay in which analyte to be measured sandwich btw two Antibodies

Introduction

Fluorescent and radioactive antibodies have been used to locate or measure solid-phase antigens for many years. However, only recently has the labeled antibody been applied to measurement of antigen to sample. The method converts the unknown antigen into a traceable radioactive product. Immunoradiometric assay (IRMA) was first introduced by "Miles and Hales" in 1968, who proposed certain theoretical advantages of the method with regard to improving the sensitivity and precision of immunoassays.

Principle

In IRMA, the antibodies are labeled with radioisotopes which are used to bind antigens present in the specimen. When a positive sample is added to the tubes, radioactively labeled (labeled with I125 or I131 radioisotopes) antibodies bind to the free epitopes of antigens and form an antigen-antibody complex. Unbound labeled antibodies are removed by a second reaction with a solid phase antigen. The amount of radioactive remaining in the solution is direct function of the antigen concentration.

References

Immunologic tests {{Immunology-stub