"Type O" redirects here. For other uses, including type 0, see Type 0. For typographical errors, see typo.
The ABO blood group system is used to denote the presence of one, both, or neither of the A and B antigens on erythrocytes.[1] For human blood transfusions, it is the most important of the 44 different blood type (or group) classification systems currently recognized by the International Society of Blood Transfusions (ISBT) as of
December 2022.[2][3] A mismatch (very rare in modern medicine) in this, or any other serotype, can cause a potentially fatal adverse reaction after a transfusion, or an unwanted immune response to an organ transplant.[4] 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.
^Schreiber BA, Curley R, Gaur A, Rodriguez E, Rogers K, Sinha S (18 July 2017). "ABO blood group system". Encyclopædia Britannica. Encyclopædia Britannica, Inc. Retrieved 26 October 2017.
^Maton A, Hopkins J, McLaughlin CW, Johnson S, Warner MQ, LaHart D, Wright JD (1993). Human Biology and Health. Englewood Cliffs, New Jersey, USA: Prentice Hall. ISBN978-0-13-981176-0.