I disagree with Konceptual. I don't really know why but the JW take the Blood issue way more seriously than any other teaching from the WT. I have seen not few cases of people who were disfellowshipped or inactive who didn't take blood.
By the way, I always thought that it's easier to "plan" not to take blood in a previously set surgery, for example. I believe, however, that in case of an accident and they need the blood just to stay alive until the doctors finish the surgery in the spur of the moment, it's not so simple to stick to their "morals".