Sanguimancy

Blood magic has been under serious scrutiny for hundreds of decades because of its powerful effects on organic bodies and its use in rituals most individuals would find distasteful, to say the least. Magic power is surged through the blood to control it, but once controlled and let go, that blood becomes unusable to blood magic. Throw a blood spike, lose a blood spike. More powerful when using one's own blood, with the associated risks.
Today, it is still viewed like one would view a recently released convict; with suspicion. Even with the Truespoken Dynasty damning the practice into oblivion, the Empire has allowed the practice to be learned by responsible individuals from experienced individuals due to its beenficial potential in health and medicine.
In more recent times, it’s been an educational subject in schools of magic for young mages to learn. Its manipulation of bodies consisting of organic matter can indeed have terrifying effects and disgusting implications. But, while in the professional sphere of magic the practice may not be well-liked even by those using it, it’s respected for its mutational and healing properties and is still alive and present in wizarding culture, particularly within the borders of Halshafen.
One of the reasons for its popularity is the concept of the Bloodborn.