The answer is immunizations. I had this question before.
They are not warning the viewers about the possible effects of alcohol. They don't tell them that drinking too much is bad for your body and can cause you to pass out or even die from alcohol poisoning. Alcohol can alter your brain and cause you to make decisions that you normally wouldn't make, which can greatly affect your life.
Knowing the ABO blood type of a potential donor is only the first step. It is important to test Rh and test the blood to ensure there a no diseases that would harm the patient.