Provided below are ELISA kits targeting X antigen family member 3, a human protein encoded by XAGE3. This protein is 111 amino acids long, with a mass of 12.3 kDa, and is a member of the GAGE family. Other alias names for this protein include: CT12.3, G antigen family D 4, cancer/testis antigen 12.3, cancer/testis antigen family 12 member 3a, g antigen family D member 4, placenta-specific 6, and placenta-specific gene 6 protein.