Immunoradiometric assay

Immunoradiometric assay is an assay that differs from conventional radio immunoassay in that the compound to be measured combines directly with radioactively labeled 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 tracable radioactive product. Immuno radiometric assay (IRMA) was first introduced by "Miles and Hales" in 1968.

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 I135 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.