Human blood is not Biblically forbidden in consumption due to the blood prohibition. Nevertheless, it is [Rabbinically] forbidden to drink visible human blood which has separated from a human body due to Maaras Ayin.
Blood fell into food: If human blood fell into one’s food, the food remains permitted [irrelevant of the ratio]. This allowance applies even if the blood is the majority of the mixture. This however only applies if the blood, and color of the blood, is not recognizable within the food. However if the food now has a reddish tinge it is forbidden even if it has a 1:60 ratio. Likewise, it is forbidden to initially mix the blood into the food, and only if after the fact the blood became mixed in, we rule that it is permitted, even if he mixed it in intentionally. In the event that the blood is still recognizable within the mixture, one may add more food to the mixture in order to nullify its color.
 See Darkei Teshuvah 66/66 for a discussion in Poskim as to why it is not Biblcially forbidden just as human meat is forbidden.
 Rama ibid; Hagahos Maimanis 7; Rashba in Toras Habayis 3/5
 The reason: As from the letter of the law human blood is permitted [Michaber ibid], and it is only due to Maaras Ayin that we refrain from eating it, therefore if it fell into a food the food is permitted without nullification as is always the law by Maaras Ayin. [Peri Megadim 66 S.D. 16]
 Peri Megadim ibid based on Bach
 Glosses of Yad Avraham; Darkei Teshuvah 66/71 based on Migdal Oz on Rambam chapter 6 of Machalos Assuros
 Toras Chatas 62/14; Darkei Teshuvah 66/67
 Darkei Teshuva ibid; See Minchas Yakaov62/18; Yad Yehuda Haaruch 66/12 and Katzar 18