Fibroblast growth factor 23 (FGF23) is a 3032 kDa member of the FGF family, within a subfamily that also includes FGF19 and FGF21. FGF23 is produced by osteocytes and osteoblasts in response to high circulating phosphate levels, elevated parathyroid hormone, and circulatory volume loading and it plays a central role in chronic kidney disease-mineral bone disorder and is associated with CKD progression and cardiovascular morbidity. Researches show that FGF23 can directly targets cardiac myocytes via Fibroblast Growth Factor Receptor 4 (FGFR4), thereby inducing hypertrophic myocyte growth and the development of left ventricular hypertrophy (LVH) in rodents. Thus a functional binding ELISA assay was conducted to detect the interaction of recombinant mouse FGF23 and recombinant human FGFR4. Briefly, biotin-linked FGF23 were diluted serially in PBS, with 0.01% BSA (pH 7.4). Duplicate samples of 100 ul were then transferred to FGFR4-coated microtiter wells and incubated for 1h at 37℃. Wells were washed with PBST 3 times and incubation with Streptavidin-HRP for 30min, then wells were aspirated and washed 5 times. With the addition of substrate solution, wells were incubated 15-25 minutes at 37℃. Finally, add 50 µl stop solution to the wells and read at 450 nm immediately. The binding activity of FGF23 and FGFR4 was shown in Figure 1, the EC50 for this effect is 0.074 ug/mL.