IMMUNOASSAY OF INSULIN-LIKE GROWTH-FACTOR BINDING PROTEIN-1

Accurate measurement of insulin-like growth factor (IGF) binding prote in-1 (IGFBP-1) is important for precise definition of its physiologica l roles and potential diagnostic values. Because altered phosphorylati on results in altered IGFBP-1 immunoreactivity, current assays may sig nificantly underestimate or fail to detect physiological changes in th e IGFBP-1 concentrations. We developed three ELISAs (ELISA 1-3) using a common capture but three different detection antibodies. IGFBP-1 in serum, synovial fluid (SF), cerebrospinal fluid (CSF), and amniotic fl uid (AF) were measured before and after treatment with alkaline phosph atase (ALP). Among the methods, only ELISA-1 was unaffected by IGFBP-1 phosphorylation and generated identical results before and after ALP treatment. The serum and SF values by ELISA-2 and -3 were lower by sim ilar to 4- to 10-fold, but increased after ALP treatment to within 66- 98% of those by ELISA-1. The medians in AF, and to a lesser extent in CSF, by all methods were similar and did not change significantly afte r dephosphorylation. ELISA-1 showed excellent correlation with ELISA-2 , ELISA-3, and a commercial IGFBP-1 IRMA only after ALP-treated sample s were analyzed by the comparative methods. ELISA-1 is highly specific for IGFBP-1 and demonstrated acceptable analytical performance charac teristics.