A compound attribute that is the ratio of amount of ephrin-A4 (human) in blood to amount of histamine N-methyltransferase (human) in blood. The trait is EFNA4/HNMT protein level ratio in blood (Ontology of Biological Attributes entry OBA_2055595). Also known as: the ratio of amount of ephrin-A4 (human) in blood to amount of histamine N-methyltransferase (human) in blood.