A compound attribute that is the ratio of amount of follistatin-related protein 3 (human) in blood to amount of spondin-2 (human) in blood. The trait is FSTL3/SPON2 protein level ratio in blood (Ontology of Biological Attributes identifier OBA_2054185). Also known as: the ratio of amount of follistatin-related protein 3 (human) in blood to amount of spondin-2 (human) in blood.