@ dubstepped: Who said blood transfusions were without risk?
OrphanCrow said that: "blood transfusions are the safest procedure available to the medical profession. The safest. That is a fact. Blood transfusions are the only medical procedure that reaches a six sigma safety rating."
A six sigma safety rating is the equivalent to the occurrence of 3.4 defects per million opportunities - a defect is everything that does not meet customer requirements such as even staying in the hospital one day longer than required or a mistake during the procedure.
https://www.isixsigma.com/industries/healthcare/six-sigma-powerful-strategy-healthcare-providers/
Interestingly The Serious Hazards Of Transfusion - SHOT - is the United Kingdom’s independent, professionally-led haemovigilance scheme, which is funded by the four British Blood Transfusion Services and is based at the Manchester Blood Centre, UK.
They collect statistical data, and present an annual review - 2016 hasn't been published yet, so the latest one is 2015.
http://www.shotuk.org/