Fully biologically active when compared to standard. The ED50 as determined by thymidine uptake assay using FGF-receptors transfected BaF3 cells is less than 0.5 μg/ml, corresponding to a specific activity of > 2.0 × 103 IU/mg in the presence of 0.3 µg/ml of rMuKlotho and 10 μg/ml of heparin.