The Phospho-BTK (Tyr551) Fluorometric Cell-Based ELISA Kit provides a lysate-free, convenient, and high-throughput approach for monitoring Phospho-BTK (Tyr708) protein phosphorylation and expression profile in cells. The kit can be used for measuring the relative amounts of phosphorylated Phospho-BTK (Tyr708) in cultured cells as well as screening for the effects that various treatments, inhibitors (ie. siRNA or chemicals, or activators have on CAV1 phosphorylation.