Fig. 4.

PTH ligand binding assay evolution. A) The first-generation radioimmunoassays used a single antibody directed against the residues within the sequences 44–68 or 53–84. B) Second-generation immunoassays were two-site sandwich assays with capture antibodies directed against residues 1–34 or 1–38 and detection via residues 39–84 or 53–84. C) The third-generation immunoassays were optimized to detect intact PTH (residues 1–84) using a capture antibody targeting the C-terminus (epitope within residues 39–84) and a detection antibody targeting the N-terminus (residues 1–4).