Radioimmunomääritys

Radioimmunomääritys, often abbreviated as RIA, is a widely used in vitro technique for measuring the concentration of various substances in biological samples. It combines the principles of radioimmunoassay and immunoassay. The core of RIA lies in the competition between an unlabeled antigen in the sample and a radioactively labeled antigen for a limited number of binding sites on a specific antibody.

The procedure typically involves incubating a known amount of antibody with a fixed quantity of radiolabeled antigen and the sample containing the unlabeled antigen. The unlabeled antigen in the sample will bind to the antibody, displacing the radiolabeled antigen. The higher the concentration of unlabeled antigen in the sample, the more radiolabeled antigen will be displaced.

After the incubation period, the antibody-bound antigen (both labeled and unlabeled) is separated from the unbound antigen. This separation is usually achieved through precipitation methods, such as using a second antibody that precipitates the first antibody-antigen complex, or by using solid-phase techniques where the antibody is immobilized on a surface. The radioactivity of the separated bound fraction is then measured using a gamma counter.

A standard curve is generated by plotting the radioactivity of the bound fraction against known concentrations of unlabeled antigen. The concentration of the antigen in an unknown sample is then determined by comparing its measured radioactivity to this standard curve. RIA is known for its high sensitivity and specificity, making it suitable for detecting very low concentrations of analytes like hormones, drugs, and proteins. However, the use of radioactive isotopes requires specialized handling and disposal procedures.