Repligen’s LONG®R3IGF-I ELISA is the only commercially available kit for the quantitation of LONG®R3IGF-I. Vital when developing cell culture and purification processes, in order to optimize the concentration and demonstrate clearance, Repligen’s LONG®R3IGF-I ELISA kit is fast, accurate, and easy-to-use with both media and drug substance samples. In addition, the ready-to-use ELISA plate allows the assay to be run immediately without additional plate coating and blocking steps. With well characterized accuracy and precision, this sandwich ELISA uses a biotinylated secondary antibody and Streptavidin-HRP for detection (Tables 1 & 2). As the only commercially available kit specifically designed for the quantitation of LONG®R3IGF-I, it has limited reactivity to native or recombinant IGF-1 and no reactivity to Insulin (Figure 1).