How can a person find out their blood type?

Blood type can be determined by having a doctor run a blood test. Each blood type has different antigens found in the blood.

Blood type is genetic. A person's blood type is determined by the type that both parents have, reports the American Red Cross. There are four main types of blood: A, B, AB and O. Each of these have a positive and negative, meaning there are actually eight variations of blood. People can determine their blood type by having a test done or determining which blood type both of their parents have. O+ is the most common blood type in the world and a person with this type can donate blood to any other blood type.