Based on the common ABO blood typing process, a person's blood type could be A, B, AB, or O. It is very important for people to know their own blood type, as well as that of their spouse and children. Important decisions regarding emergency blood transfusions may need to be made quickly, so having this information on hand for medical professionals can shave precious minutes off the initial triage process after trauma. A person's blood type is largely determined by genetics, and does not change throughout your life. A simple blood typing test can be performed literally anywhere by anyone through the use of specially treated test cards.
One of the main factors that determines blood type is family genetics. A child receives separate sources of genetic code, called alleles, from each parent at the time of conception. One of the alleles located on chromosome 9 contains the exact type of the donor parent and is classified as A, B, AB, or O. An additional factor is called the Rhesus factor, which could be positive or negative. The actual blood type of a child is determined by the dominant type between the two parents. A and B are dominant over O, which means that a child who receives an A from the father and an O from the mother will have type A blood.
Subsequently, A and B are considered to be codominant, meaning that a child who inherits an A from the mother and a B from the father will likely have an AB blood type. Just two recessive O genes from both parents will result in a child having type O. An O negative blood type is considered a universal donor, as it contains nothing that would appear foreign to someone else's blood. Those who are type A or B positive should not receive blood infusions of the opposite type, as the body's natural defenses will attack the incoming blood cells as they would any other infection.
A person's blood type is determined by a simple ABO test available at a doctor's office, blood donation center, or even through pharmacies. A drop of blood is placed on two separate test circles marked A and B. The card has already been prepared with dried serum containing anti-A and anti-B chemicals. If the blood reacts to circle A but not to circle B, then the tester's blood type is considered to be A. A reaction to both circles indicates type AB, while a complete non-reaction to either circle indicates type O blood. The reaction is caused by the chemicals on the card coming into contact with the type A or type B antigens on the surface of the red blood cells.