Praise be to Allah.
It is not permissible to sell blood, because of the report in Saheeh al-Bukhaari from the hadeeth of Abu Hudhayfah, who said: “I saw my father buy a cupper [a person who does cupping] and order that his tools be broken. I asked him about that and he said, ‘The Messenger of Allaah (peace and blessings of Allaah be upon him) forbade the price of blood, .....’” (Al-Bukhaari, 3/12,43; Ahmad, 4/308, 309). Al-Haafiz said in al-Fath: what is meant by the prohibition of blood is the same as the prohibition of dead meat and pork. It is haraam according to scholarly consensus, i.e., selling blood and taking its price. And Allaah knows best.