Caeruloplasmin (also spelled ceruloplasmin) is the major copper-carrying protein in the blood, produced by the liver. It transports approximately 65–70% of copper in the circulation and plays an essential role in copper metabolism, iron oxidation (ferroxidase activity), and antioxidant defence. Because caeruloplasmin is an acute phase reactant, it rises with inflammation alongside CRP and other acute phase proteins.

Caeruloplasmin testing is primarily used to investigate Wilson's disease — a rare genetic disorder of copper transport where caeruloplasmin is markedly reduced and copper accumulates in the liver, brain, and other organs, causing liver disease, neurological symptoms, and psychiatric disturbances. It is also used in the investigation of unexplained liver disease, movement disorders, and as part of copper status assessment.