A compound attribute that is the ratio of amount of ephrin-A4 (human) in blood to amount of ephrin type-B receptor 6 (human) in blood. The trait is EFNA4/EPHB6 protein level ratio in blood (Ontology of Biological Attributes term OBA_2055594). Also known as: the ratio of amount of ephrin-A4 (human) in blood to amount of ephrin type-B receptor 6 (human) in blood.