A compound attribute that is the ratio of amount of histamine N-methyltransferase (human) in blood to amount of retinol-binding protein 5 (human) in blood. The trait is HNMT/RBP5 protein level ratio in blood (OBA_2053062). Also known as: the ratio of amount of histamine N-methyltransferase (human) in blood to amount of retinol-binding protein 5 (human) in blood.