A compound attribute that is the ratio of amount of adenine phosphoribosyltransferase (human) in blood to amount of CD63 antigen (human) in blood. The trait is Ontology of Biological Attributes identifier OBA_2053923 (APRT/CD63 protein level ratio in blood). Also known as: the ratio of amount of adenine phosphoribosyltransferase (human) in blood to amount of CD63 antigen (human) in blood.