My wife is a phlebotomist (a medical professional who takes blood) and she often says it's hard to find veins in older people and small children. She sometimes draws from patients who are scared of the needle. If you're one of those, here is some good news for you.
Contrary to what you may have seen on True Blood, there is no substitute for human blood, and The American Red Cross has issued an emergency call for blood and platelet donors of all blood types.