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The question: How useful is it to know my blood type? What can it tell me about myself?

The answer: It can be helpful to know your blood type for a number of reasons. Let's review how your blood type is determined to understand why it's important and how it can effect your health.

Your blood type is inherited from your parents and is determined by two factors: the ABO grouping system and the Rh factor. Starting with the ABO system, there are four blood groups: A, B, AB and O. The type of blood you have is based on the presence or absence of antigens and antibodies in your blood. Antigens are proteins that stick to the surface of your red blood cells, while antibodies are produced in the plasma or liquid portion of the blood. The type of antigen you have tells us what your blood type is. For example, if you have A antigens on your blood cells, your blood type is A. If someone has both A and B antigens, they are type AB. And if you do not have any antigens, your blood type is O. For each antigen on the blood cell, the opposite antibody is produced in the plasma. For example, type B blood has anti-type A antibodies.

For a detailed summary with interesting facts about each blood type, visit the Canadian Blood Services. In addition to the ABO typing system, your blood type is also determined by the presence or absence of another antigen known as the Rh factor. For example, if you are Rh-negative and have A-type blood, you are A-negative; if you have B-type blood and are also Rh-positive, you are B-positive. While there are more than 20 blood-type systems, ABO and Rh are the most important ones.

The importance of knowing your blood type is to prevent the risk of you receiving an incompatible blood type at a time of need, such as during a blood transfusion or during surgery. If two different blood types are mixed, it can lead to a clumping of blood cells that can be potentially fatal. Thankfully, prior to doing a blood transfusion, your blood type is tested and cross-matched against the donor blood, which minimizes the risk of transfusion reaction.

Knowing your Rh blood type is also important for pregnant women. If a women is Rh-negative and pregnant with a baby who is Rh-positive, it can lead to a condition known as Rh-incompatibility. If the blood of the Rh-positive baby mixes with the mother's, it can trigger the production of antibodies against the baby's blood known as Rh-sensitization. In general, the production of these antibodies will not affect the baby during the pregnancy where sensitization occurred, but future pregnancies with Rh-positive babies can lead to a fatal outcome for the baby. To avoid this risk, we always check a woman's blood type early in pregnancy. If she is Rh-negative, she receives a shot called immunoglobulin which prevents antibody production and sensitization.

One of the most valuable reasons to know about your blood type is to help others. Canadian Blood Services are often looking for potential donors and will put a call out to the public when there is a need to help others who have been in accidents, are in cancer treatment or need surgery. Sometimes they will put out a call for specific blood types, so when you hear that your type is in need, it's your opportunity to roll up your sleeve and donate to help others.

Dr. Sheila Wijayasinghe is the medical director at the Immigrant Womens' Health Centre, works as a staff physician at St. Michael's Hospital in their Family Practice Unit and at Hassle Free Clinic, and established and runs an on-site clinic at Women's Habitat Shelter in Etobicoke.

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