ABO blood group system

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A system used to group human blood into different types, based on the presence or absence of certain markers on the surface of red blood cells.

ABO blood type
ABO blood type

Blood groups

The four main blood types are A, B, O, and AB.

ABO donation
ABO donation path

Use in clinical practice

  • For a blood transfusion, the ABO blood group system is used to match the blood type of the donor and the person receiving the transfusion.
  • People with blood type O can donate blood to anyone and are called universal donors.
  • People with blood type AB can accept blood from all donors and are called universal recipients.
  • People with type A or B can receive matching blood or type O blood.

ABO antigens

  • The A antigen and the B antigen are derived from a common precursor known as the H antigen (or H substance).
  • The H antigen is a glycosphingolipid (sphingolipid with carbohydrates linked to the ceramide moiety).
  • Since it lacks N-acetylneuraminic acid (sialic acid) it is referred to as a globoside, not a ganglioside.
  • In blood group O the H antigen remains unchanged and consists of a chain of galactose, N-acetylglucosamine, galactose, and fructose attached to the ceramide.
  • H antigens can be changed into A or B antigens by enzymes coded by the blood group A or B genes.
  • Type A has an extra N-acetyl galactosamine bonded to the galactose near the end, while type B has an extra galactose bonded to the galactose near the end.
  • Antibodies are not formed against the H antigen, except by those with the Bombay phenotype.
  • In secretors, ABH antigens are secreted by most mucous-producing cells of the body interfacing with the environment, including lung, skin, liver, pancreas, stomach, intestines, ovaries and prostate.

History of discoveries

The ABO blood groups system is widely credited to have been discovered by the Austrian scientist Karl Landsteiner in 1901.


  • The newborn do not have anti-A or anti-B antibodies.
  • In the first years of life it is thought that environmental antigens (bacterial antigens and perhaps plant antigens) are similar enough to the A and B glycoprotein, and that antibodies created against the bacteria will react to ABO-incompatible red blood cells. Generally anti-A and anti-B antibodies are IgM, which are not able to pass through the placenta to the fetal blood circulation.

ABO hemolytic disease of the newborn

ABO blood group incompatibilities between the mother and child does not usually cause HDN because antibodies to the ABO blood groups are usually of the IgM type, which do not cross the placenta; however, sometimes IgG ABO antibodies are produced and a baby can develop ABO HDN.

Latest research - ABO blood group system

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