A compound attribute that is the ratio of amount of ephrin-A4 (human) in blood to amount of tumor necrosis factor receptor superfamily member 9 (human) in blood. The trait is Ontology of Biological Attributes id OBA_2055600 (EFNA4/TNFRSF9 protein level ratio in blood). Also known as: the ratio of amount of ephrin-A4 (human) in blood to amount of tumor necrosis factor receptor superfamily member 9 (human) in blood.