Anti-AFP antibodies are used in the immunodetection of the protein alpha fetoprotein. In humans, the canonical protein has a reported length of 609 amino acid residues and a mass of 68.7 kDa. It has been described to be a secreted protein. It is notably expressed in plasma. A member of the ALB/AFP/VDB protein family, AFP is known to bind copper, nickel, and fatty acids as well as, and bilirubin less well than, serum albumin. Post-translational modifications have been described, including protein cleavage, sulfation and glycosylation. The AFP gene has been associated with the disease, Alpha-fetoprotein deficiency. Synonyms for this target antigen include FETA, HPAFP, alpha-1-fetoprotein, alpha-fetoglobulin, and AFPD. AFP gene orthologs have been reported in the mouse, rat, bovine, chimpanzee and chicken species.