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A vital part of our immune system is the tagging of our own cells and tissues. ABO blood types are part of our self-tagging mechanism.

The safest and easiest blood transfusions are between people with the same ABO blood type.

The ABC of ABO

Blood is a vital, multi-functional tissue

Blood consists of red blood cells that carry oxygen, white blood cells that fight infection, platelets that help control bleeding, and plasma which is the fluid that transports these essential cells around the body’s circulatory system. The plasma also contains antibodies, proteins which the immune system produces to neutralize or destroy foreign substances that enter the body. The substances that stimulate the production or mobilization of antibodies are called antigens.

The immune system is the body’s defense mechanism

The immune system is the body’s defense mechanism against infectious organisms, viruses and other potentially harmful foreign substances. The immune system is a complex network of cells, tissues, and organs that work together to protect the body. Through a series of steps called the immune response, the immune system attacks organisms and substances that invade the body and can cause disease. One of these steps is the antigen-antibody reaction.

Antigen-Antibody reactions are an important part of the immune response

Microorganisms or foreign substances that invade the body typically include molecules that do not occur naturally in our bodies – the antigens. For the purpose of identifying invading substances, the immune system has an extremely variable set of detector molecules – the antibodies. When the body’s immune system detects an antigen using such antibodies, several types of cells work together to recognize it and mount a response. One such response is to make more copies of the antibodies that recognized the antigen. In this way, the immune system starts to prepare itself for a large-scale invasion of potentially harmful invaders.

Our immune system develops a “memory” for antigens

Once the immune system has learnt to recognize particular antigens, it develops a “memory” for the antigen and will immediately produce the appropriate antibodies to help neutralize or remove the “invader” the next time the antigen is encountered by the immune system. The key to a healthy immune system is its remarkable ability to distinguish between the body’s own cells, recognized as “self,” and foreign cells, or “non-self.” A person’s plasma does not normally contain any antibodies that will bind to molecules that are part of his or her own body.

ABO blood types are part of our self-tagging mechanism

In general, the immune system’s task is to identify and destroy biological materials which are foreign to the body. In order to perform this task, the immune system needs to know how to distinguish between what belongs to us and what is an invader. So a vital point early in the development of our immune system is the destruction of antibodies that recognize the molecules that are natural to our own body. If this were not accomplished, then our immune system would attack our own cells.

AB antigens on our red blood cells determine which AB antibodies we carry

The immune systems of people of blood type A produce antibodies that recognize the B glycoprotein, whereas people of blood type B produce antibodies that recognize the A glycoprotein. People of blood type O produce both kinds of antibodies, but those of blood type AB produce neither kind of antibody.

ABO blood type antigens can also be found in secreted fluids

ABO blood type antigens are not only found on the surface of red cells. They are also normally secreted by some people in their body fluids, including saliva, tears, and urine. Whether someone is able to secrete them is genetically controlled.

ABO blood types must be matched for blood transfusions

The safest and easiest blood transfusions are between people with the same ABO blood type. However, it is possible for people of blood type AB to receive blood transfusions from anyone, as long as the antibodies from the donor have been removed. Similarly, individuals of blood types A and B can receive blood of type O if the antibodies have been removed. This is why people of blood type O are sometimes called “universal donors”. However, even type O negative blood may have antibodies that cause serious reactions during a transfusion, so ideally, blood transfusions are done with donated blood that’s an exact match for ABO blood type and Rh factor. A transfusion of blood type A to a person of blood of type B or vice-versa would however cause a severe immune response and a medical emergency.

	Donor blood type
Recipient blood type	A	B	O	AB
A	Yes	No	OK	No
B	No	Yes	OK	No
O	No	No	Yes	No
AB	OK	OK	OK	Yes

NO: heavy and dangerous agglutination of donor´s cells would take place in recipient,
OK: no agglutination of donor´s cells, but antibodies in donor´s blood may cause some agglutination of recipient´s cells, not considered dangerous. The OK therefore applies to packed red blood cells and not to whole blood products;
Yes: the perfect match, no agglutination of donor´s cells would happen.

So, this means that

• if you have type A blood, you can only receive types A and O blood
• if you have type B blood, you can only receive types B and O blood
• if you have type AB blood, you can receive types A, B, AB, and O blood
• if you have type O blood, you can only receive type O blood

Knowing your ABO blood type is critically important

When a person needs to receive a blood transfusion or have an organ transplant, it is critically important to match ABO blood types of donor and recipient. Since antibodies are carried in the liquid part of blood (plasma), both blood and plasma transfusions must be matched to avoid a life-threatening antigen-antibody immune reaction in the recipient.

There are several other blood type systems. One of these, the so-called Rhesus system, is also important for matching blood or organ donors and recipients. The two Rhesus blood types are called positive and negative. This factor is especially important to know during pregnancy, as problems can arise when the fetus’s blood has the Rh factor (is Rh+) and the mother’s blood does not (Rh-), a condition known as Rhesus disease. Please note that the deCODEme scan does not at this time identify the Rhesus blood type.

Please note that the results of the deCODEme scan cannot replace a traditional ABO blood typing test that is used for critical medical procedures such as blood transfusion or organ transplantation. What we provide here is a prediction of your ABO blood type based on the genetic variants included in the deCODEme Complete Scan.

This content was last reviewed on February 09, 2010.

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