Two-Sites Immunoradiometric Assay Using Monoclonal Antibodies for the Determination of Serum Human Sex Hormone Binding Globulin

Abstract

An immunoradiometric assay (IRMA) for the determination of human Sex Hormone Binding Globulin (SHBG) in serum is described. This IRMA uses three mouse monoclonal antibodies.

Two monoclonals anti-human SHBG are coated on tubes and used as capture antibodies. The third monoclonal labeled with ¹²⁵I completes the system, allowing the formation of the “sandwich”.

The detection limit of the assay is 2.5 femtomol SHBG per tube (250 pg/tube). Using this test for the measurement of SHBG and radioimmunoassays for the determination of total Testosterone and Estradiol, we calculated the Free Androgen Index (FAI) and the Free Testosterone. The results obtained were compared with the values of Free Testosterone measured by equilibrium dialysis.

There is a close correlation between both calculated parameters and the levels of Free Testosterone, validating this SHBG assay.

Key Words:

• sex hormone binding globulin
• monoclonal antibodies
• immunoradiometric assay
• free androgen index
• free testosterone