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ABO blood group system

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ABO blood group system

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classification of blood types

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blood type
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ABO blood group system
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Encyclopedic overview

ABO blood group antigens present on red blood cells and IgM antibodies present in the serum

The ABO blood group system is used to denote the presence of one, both, or neither of the A and B antigens on erythrocytes (red blood cells). For human blood transfusions, it is the most important of the 48 different blood type (or group) classification systems currently recognized by the International Society of Blood Transfusions (ISBT) as of June 2025. A mismatch in this serotype (or in various others) can cause a potentially fatal adverse reaction after a transfusion, or an unwanted immune response to an organ transplant. Such mismatches are rare in modern medicine. The associated anti-A and anti-B antibodies are usually IgM antibodies, produced in the first years of life by sensitization to environmental substances such as food, bacteria, and viruses.

Excerpted from Wikipedia’s “ABO blood group system” article, available under the CC BY-SA 4.0 licence.

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