Ilove-Years ago I worked at a hospital as a go-fer. I would have to go to the lab to pick up blood for the patients. This required cross checking the name on the bag and so forth. The blood bags were labelled "bio-hazard", which was rather alarming. It wasn't all that common to have to pick blood up. The doctors didn't order it lightly, it wasn't like they were ordering up Tylenol, they ordered it up knowing that it was a source of contamination for their patient, but after considering their other options, they did order it when it was their best defense for what was going on with that particular patient.
I would personally never lightly take a blood transfusion, but then most doctors would never lightly order up a blood transfusion either.