Ligand-mediated immunofunctional hormone binding protein assay method

A ligand mediated immunofunctional method for determining the amount of a polypeptide hormone binding protein selected from the group consisting of a growth hormone binding protein factor, an epidermal growth factor binding protein, an insulin-like growth factor (IGF) binding protein, a platelet derived growth factor (PDGF) binding protein, a nerve growth factor (NGF) finding protein, an insulin binding protein, a corticotropin releasing factor (CRF) binding protein, a transforming growth factor beta (TGF-.beta.) binding protein and an activin binding protein in a liquid sample comprising:

• (a) contacting said liquid sample with:
• 1) a first antibody attached to a solid phase carrier, wherein said first antibody is specific for epitopes on said polypeptide hormone binding protein such that in the presence of antibody the hormone binding sites remain available on the binding protein for binding to the ligand polypeptide hormone, thereby forming a complex between said first antibody and said polypeptide hormone binding protein;
• and 2) said ligand polypeptide hormone for a period of time sufficient to saturate all available ligand hormone binding sites on said polypeptide hormone binding protein thereby forming a saturated complex;
• (b) contacting said saturated complex with a detectably labeled second antibody which is specific for epitopes on said ligand polypeptide hormone which are available for binding when said ligand polypeptide hormone is bound to said polypeptide hormone binding protein;
• and
• (c) quantitatively analyzing the amount of said labeled second antibody bound as a measure of said polypeptide hormone binding protein in said liquid sample.