Fibroblast growth factor 23 (FGF-23) is a phosphaturic peptide involving in the development of hypophosphatemic rickets/osteomalacia. FGF-23 assays are known to be useful for the diagnosis of hypophosphatemia. Now three different two-site enzyme-linked immunosorbent assays a C-terminal human FGF23 enzyme-linked immunosorbent assay (ELISA) (Immunotopics, California), an intact human FGF23 ELISA (Immunotopics, California), and another intact human FGF23 ELISA (Kainos Laboratories, Japan) are available for the diagnosis.