Blood typing is a method to tell what type of blood you have. Blood typing is done so you can safely donate your blood or receive a blood transfusion. It is also done to see if you have a substance called Rh factor on the surface of your red blood cells.

Your blood type is based on whether or not certain proteins are on your red blood cells. These proteins are called antigens. Your blood type (or blood group) depends on what types your parents passed down to you.The placement of the A and B antigens is dependent upon the existence of a substrate produced by the Hh blood group system (ISBT # 018). Some individuals have weakened or variant expression of A and/or B which can be attributed to inheritance of variant forms of transferases. Those individuals that have neither transferases, inheritors of two amorph genes, are group O. To date, 14 A alleles, 14 B alleles and 8 O alleles have been identified at the molecular level and more remain to be found. The ABO antigens, as stated above are not restricted to the red blood cell membrane but can be found in saliva and all body fluids except spinal fluid if the individual has inherited a secretor gene. The antigens are also found on most epithelial and endothelial cells. It also appears on lymphocytes and platelets as it is adsorbed from the plasma. Alterations of ABH expression have been found in various forms of cancer. Furthermore, antigens of the ABO system may play a role in resistance to bacteria or viruses.

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