Ready-to-use ELISA kits are available for the detection of cyclic AMP-regulated phosphoprotein, 21, an alias of the protein, cAMP regulated phosphoprotein 21. The official gene symbol is ARPP21. The protein, with a mass of 89.2 kDa and length of 812 residues, is reported to be cytoplasmic. It may be known by other names, including: RCS, R3HDM3, thymocyte cAMP-regulated phosphoprotein, cyclic AMP-regulated phosphoprotein 21 kD, cAMP regulated phosphoprotein 21kDa, and R3H domain containing 3.