Estimation of serum sex hormone-binding globulin by five direct and two indirect methods.

Serum sex hormone-binding globulin (SHBG) has been estimated over the range 2-190 nM by six commercially available methods. The Farmos immunoradiometric assay (IRMA) and the Pharmacia-LKB DELFIA fluoroimmunoassay, which use the same monoclonal antiserum, produced statistically identical but widely spread results. The Techland polyclonal radioimmunoassay produced similar results but was considerably less sensitive, and agreement with the other two direct methods was poor at low concentrations. These three direct methods gave slightly higher results than those obtained with the two indirect methods: the BioMerieux concanavalin-A-binding method and, especially, the Serono ammonium sulphate precipitation method. The Diagnostic Products monoclonal IRMA gave results that were up to double the values obtained with the other five methods and is considered unsatisfactory. Monoclonal antibodies are now available for the direct estimation of SHBG, although an amino acid sequence has not yet been published for this protein, and there is still some controversy about the size of its structural units.