Giovanni Battista Cybo, from a well-to-do Genovese family, served as Pope Innocent VIII from 1484 until his death on July 25, 1492. Known for a luxurious lifestyle and appointing his children to high office, his papacy faced financial insolvency and constant conflict with Naples. He also issued a Papal Bull in 1492, which expelled all Jews from the Papal States.
In one of the last chapters of his life, as written by Horace M. Brown in 1917, Pope Innocent VIII is said to have received, at the behest of a Jewish physician, Abraham Meyre of Balmes, a transfusion of blood in June of 1492 from three ten-year-old boys, each of whom was paid a ducat and all of whom died after having their blood drawn. Brown's source for this first known blood transfusion was Stefano Infessura's Diarium Urbis Romae (Diary of the City of Rome), in which he alleged that in July 1492, a Jewish physician suggested using the blood of three children, who died from blood loss, to treat the Pope.
However, Matthew Turner and other historians have argued that this story was part of a broader anti-Semitic narrative and couldn't have possibly occurred because the technology to conduct a blood transfusion did not exist in 1492.
It is unlikely we will ever know the exact and full truth, but I believe that both of the above accounts are partially true, and only in their combination can we deduce what most likely occurred.
It is reported and not contested that Pope Innocent VIII suffered from kidney disease. Fifteenth century physicians likely did not know it was kidney failure, but could identify swelling in the legs, ankles, and eyelids, fatigue, and blood in the urine as traits of what they called Bright's Disease. It is reported that Pope Innocent VIII dealt with this affliction for a period of several years and as such it is all but certain that different physicians tried numerous different remedies to heal him.
It is extremely unlikely that the Pope who authored a Papal Bull expelling Jews would ever have been treated by a Jewish physician. However, it is also possible — and given the primary source accounting of the event, likely — that a physician attempted to administer a blood transfusion to Pope Innocent VIII. It is also likely, given the limits of technology in 1492, that this "transfusion" meant Pope Innocent VIII drank the blood to ingest it into his body rather than having it delivered intravenously.
Given that a Pope died, I believe that the underlying events are likely to have occurred, but given the anti-Semitic views of the time, it is equally likely that Infessura changed the real physician's identity to that of a Jewish physician in order to scapegoat the Jewish people for yet one more malaise — as justification for the discriminatory treatment of Jews by the Catholic Church that simultaneously spread the gospel of a loving God manifested through pastoral care, preaching, and the confessional absolution of sins.
There is too much recorded citation and too many primary source references to conclude that some sort of transfusion did not occur. It is just as unbelievable to postulate that a Jewish physician conducted it. In conclusion, I took the deductively logical elements of both conflicting views and the contextual influence of history to hypothesize that Pope Innocent VIII likely received the world's first blood transfusion from an unknown Christian physician, administered orally, from the blood of three ten-year-old boys who were each paid one ducat before dying from the ordeal.