All perfect praise be to Allah, The Lord of the Worlds. I testify that there is none worthy of worship except Allah, and that Muhammad is His slave and Messenger.
If the blood that is mixed with meat is from the veins –and most probably this is the case –then this blood is pure and its mixing with meat does not make it forbidden.
However, if the blood is poured forth (by slaughtering or the like) –and this is very unlikely to happen –then the meat must be washed before using it because this kind of blood is impure. Allah Says (what means): {Say, “I do not find within that which was revealed to me [anything] forbidden to one who would eat it unless it be a dead animal or blood spilled out or the flesh of swine — for indeed, it is impure.”} [Quran 6:145]
Allah knows best.