Blood Type Compatibility Calculator

Red cell compatibility follows from Landsteiner's rule: a person carries naturally occurring antibodies against whichever ABO antigens their own cells lack. Group A plasma holds anti-B, group B plasma holds anti-A, group O plasma holds both, and group AB plasma holds neither. These are mostly IgM antibodies that bind the transfused cells and activate complement, so an ABO-incompatible unit causes rapid intravascular hemolysis rather than a slow reaction. Because group O cells display neither A nor B antigen they are broadly transfusable, and because AB recipients make neither antibody they can accept any ABO group. Note that plasma runs the opposite way: AB plasma is the universal plasma donor and O plasma the most restricted. The Rh system behaves differently. Anti-D is not naturally present; it appears only after an Rh-negative person is exposed to D-positive cells through transfusion or pregnancy, which is why D-negative blood can be given to a D-positive patient but not the reverse, and why D-negative units are reserved for girls and women of childbearing potential. Approximate US frequencies are O positive 37 percent, A positive 36 percent, B positive 9 percent, O negative 7 percent, A negative 6 percent, AB positive 3 percent, B negative 2 percent and AB negative under 1 percent, and these vary substantially by ancestry. The critical limitation is that ABO and D are only 2 of more than 40 recognised blood group systems carrying over 300 antigens. Kell, Duffy, Kidd and MNS antibodies can all cause serious reactions in previously sensitised patients, so a serologic crossmatch and antibody screen, not a chart, govern any real transfusion.

Karl Landsteiner, then an assistant at the Institute of Pathological Anatomy in Vienna, mixed the sera and cells of his colleagues and reported in 1900 and 1901 that human blood falls into distinct groups, which he called A, B and C, the last later renamed O. His pupils Alfred von Decastello and Adriano Sturli described the fourth and rarest group, AB, in 1902. Competing notations followed, including the Roman-numeral scheme of the Czech psychiatrist Jan Jansky in 1907, until the ABO letters were standardised internationally in the 1920s. Landsteiner received the Nobel Prize in Physiology or Medicine in 1930 for the discovery. Safe transfusion needed two further advances. Sodium citrate anticoagulation, described independently around 1914 and 1915 by Albert Hustin, Luis Agote and Richard Lewisohn, allowed blood to be stored rather than transferred vein to vein, and Oswald Robertson used stored citrated blood at casualty clearing stations during the First World War. Bernard Fantus opened what he named a blood bank at Cook County Hospital in Chicago in 1937. The Rh factor was identified by Philip Levine and Rufus Stetson in a 1939 case of hemolytic disease of the newborn and characterised by Landsteiner and Alexander Wiener in 1940. Anti-D immune globulin, introduced in the late 1960s, then made Rh hemolytic disease of the newborn a largely preventable condition.