blood group

blood group, Human red blood cells (4,000× magnification).Micro Discovery/Corbisclassification of blood based on inherited differences (polymorphisms) in antigens on the surfaces of the red blood cells (erythrocytes). Inherited differences of white blood cells (leukocytes), platelets (thrombocytes), and plasma proteins also constitute blood groups, but they are not included in this discussion.

Historical background







Major human blood group systems
system date of
ABO 1901 A1, A2, B, H
MNSs 1927 M, N, S, s
P 1927 P1, P2
Rh 1940 D, C, c, E, e
Lutheran 1945 Lua, Lub
Kell 1946 K, k
Lewis 1946 Lea, Leb
Duffy 1950 Fya, Fyb
Kidd 1951 Jka, Jkb
Diego 1955 Dia, Dib
Yt 1956 Yta, Ytb
I 1956 I, i
Xg 1962 Xga
Dombrock 1965 Doa

The importance of antigens and antibodies




Chemistry of the blood group substances




Methods of blood grouping

Identification of blood groups






Coombs test

When an incomplete antibody reacts with the red cells in saline solution, the antigenic sites become coated with antibody globulin (gamma globulin), and no visible agglutination reaction takes place. The presence of gamma globulin on cells can be detected by the Coombs test, named for its inventor, English immunologist Robert Coombs. Coombs serum (also called antihuman globulin) is made by immunizing rabbits with human gamma globulin. The rabbits respond by making antihuman globulin (i.e., antibodies against human gamma globulin and complement) that is then purified before use. The antihuman globulin usually contains antibodies against IgG and complement. Coombs serum is added to the washed cells; the tube is centrifuged; and, if the cells are coated by gamma globulin or complement, agglutinates will form. Newer antiglobulin reagents (made by immunizing with purified protein) can detect either globulin or complement. Depending on how it is performed, the Coombs test can detect incomplete antibody in the serum or antibody bound to the red cell membrane. In certain diseases, anemia may be caused by the coating of red cells with gamma globulin. This can happen when a mother has made antibodies against the red cells of her newborn child or if a person makes an autoantibody against his own red cells.

Adsorption, elution, and titration

If a serum contains a mixture of antibodies, it is possible to prepare pure samples of each by a technique called adsorption. In this technique an unwanted antibody is removed by mixing it with red cells carrying the appropriate antigen. The antigen interacts with the antibody and binds it to the cell surface. These red cells are washed thoroughly and spun down tightly by centrifugation, all the fluid above the cells is removed, and the cells are then said to be packed. The cells are packed to avoid dilution of the antibody being prepared. Adsorption, then, is a method of separating mixtures of antibodies by removing some and leaving others. It is used to identify antibody mixtures and to purify reagents. The purification of the Coombs serum (see above) is done in the same way.

If red cells have adsorbed gamma globulin onto their surfaces, the antibody can sometimes be recovered by a process known as elution. One simple way of eluting (dissociating) antibody from washed red cells is to heat them at 56 °C (133 °F) in a small volume of saline solution. Other methods include use of acid or ether. This technique is sometimes useful in the identification of antibodies.

Titration is used to determine the strength of an antibody. Doubling dilutions of the antibody are made in a suitable medium in a series of tubes. Cells carrying the appropriate antigen are added, and the agglutination reactions are read and scored for the degree of positivity. The actual concentration of the antibody is given by the dilution at which some degree of agglutination, however weak, can still be seen. This would not be a safe dilution to use for blood-grouping purposes. If an antiserum can be diluted, the dilution chosen must be such that strong positive reactions occur with selected positive control cells. Titration is helpful when preparing reagents and comparing antibody concentrations at different time intervals.

Inhibition tests

Inhibition tests are used to detect the presence of antigen with blood group specificity in solutions; inhibition of a known antibody-antigen reaction by a fluid indicates a particular blood group specificity. If an active substance is added to antibody, neutralization of the antibody’s activity prevents agglutination when red cells carrying the appropriate antigen are subsequently added to the mixture. A, B, Lewis, Chido, Rogers, and P antigens are readily available and can be used to facilitate antibody identification. This technique was used to elucidate the biochemistry of ABH, Ii, and Lewis systems, and it is important in forensic medicine as a means of identifying antigens in blood stains.


Laboratory tests in which hemolysis (destruction) of the red cells is the end point are not used frequently in blood grouping. For hemolysis to take place, a particular component of fresh serum called complement must be present. Complement must be added to the mixture of antibody and red cells. It may sometimes be desirable to look for hemolysins that destroy group A red cells in mothers whose group A children are incompatible or in individuals, not belonging to groups A or AB, who have been immunized with tetanus toxoid that contains substances with group A specificity.

Hemolytic reactions may occur in patients who have been given transfusions of blood that either is incompatible or has already hemolyzed. The sera of such patients require special investigations to detect the presence of hemoglobin that has escaped from red cells destroyed within the body and for the breakdown products of other red cell constituents.

Sources of antibodies and antigens

Normal donors are used as the source of supply of naturally occurring antibodies, such as those of the ABO, P, and Lewis systems. These antibodies work best at temperatures below that of the body (37 °C, or 98.6 °F); in the case of what are known as cold agglutinins, such as anti-P1, the antibody is most active at 4 °C (39 °F). Most antibodies used in blood grouping must be searched for in immunized donors.

Antibodies for MN typing are usually raised in rabbits—similarly for the Coombs serum. Antibodies prepared in this way have to be absorbed free of unwanted components and carefully standardized before use. Additional substances with specific blood group activity have been found in certain plants. Plant agglutinins are called lectins. Some useful reagents extracted from seeds are anti-H from Ulex europaeus (common gorse); anti-A1, from another member of the pulse family Fabaceae (Leguminosae), Dolichos biflorus; and anti-N from the South American plant Vicia graminea. Agglutinins have also been found in animals—for example, the fluid pressed from the land snail Octala lactea. Additional plant lectins and agglutinins from animal fluids have been isolated.

Monoclonal antibodies (structurally identical antibodies produced by hybridomas) to blood groups are replacing some of the human blood grouping reagents. Mouse hybridomas (hybrid cells of a myeloma tumour cell and lymphocyte merging) produce anti-A and anti-B monoclonal antibodies. The antibodies are made by immunizing with either red cells or synthetic carbohydrates. In addition to their use in blood grouping, these monoclonal antibodies can be of use in defining the hereditary background (heterogenicity) and structure of the red cell antigen.

Uses of blood grouping


The blood donated by healthy persons is tested to ensure that the level of hemoglobin is satisfactory and that there is no risk of transmitting certain diseases, such as AIDS or hepatitis. It is then fractionated (split) into its component parts, particularly red cells, plasma, and platelets. Correct matching for the ABO system is vital.

The ABO and Rh groups in transfusion
system recipient type donor red cell type donor plasma type
ABO A A* or O A or AB
ABO B B or O B or AB
ABO O O only O, A, B, or AB
ABO AB AB*, A*, B, or O AB
Rh positive positive or negative positive or negative
Rh negative negative or positive**, *** negative or positive**
*Not if the patient’s serum contains anti-A1 (antibody to common type A red cell in subgroup A patients).
**Not if the patient is a female less than 45 years old (childbearing possible), unless life-threatening hemorrhage is present and transfusion of Rh-positive blood is lifesaving.
***Not if the patient’s serum contains anti-D (antibody to positive red cells), except under unusual medical circumstances.

As explained above, the most important blood group systems for transfusion of red cells are ABO and Rh. Persons who have either of the red cell antigens (A and B) have antibody present in their serum of the type that will oppose an antigen of its opposite nature; for example, group A blood contains A antigens on red cell surfaces and anti-B antibodies in the surrounding serum. On the other hand, O group individuals lack both the A and the B antigen and thus have both anti-A and anti-B in their serum. If these antibodies combine with the appropriate antigen, the result is hemolytic transfusion reaction and possibly death. Red cell transfusions must therefore be ABO compatible. The blood groups A and B have various subgroups (e.g., A1, A2, A3, and B1, B2, and B3). The only common subgroups that are likely to affect red cell transfusions are the subgroups of A.

Potential donors are also tested for some of the antigens of the Rh system, since it is essential to know whether they are Rh-positive or Rh-negative. Rh-negative indicates the absence of the D antigen. Rh-negative persons transfused with Rh-positive blood will make anti-D antibodies from 50 to 75 percent of the time. Antibody made in response to a foreign red cell antigen is usually not harmful but does require subsequent transfusions to be antigen-negative. Rh-positive blood should never be given to Rh-negative females before or during the childbearing age unless Rh negative blood is not available and the transfusion is lifesaving. If such a woman subsequently became pregnant with an Rh-positive fetus, she might form anti-Rh antibody, even though the pregnancy was the first, and the child might develop erythroblastosis fetalis (hemolytic disease of the newborn).

Care must be taken not to give a transfusion unless the cells of the donor have been tested against the recipient’s serum. If this compatibility test indicates the presence of antibodies in the recipient’s serum for the antigens carried by the donor’s cells, the blood is not suitable for transfusion because an unfavourable reaction might occur. The test for compatibility is called the direct match test. It involves testing the recipient’s serum with the donor’s cells and by the indirect Coombs test. These are adequate screening tests for most naturally occurring and immune antibodies.

If, in spite of all the compatibility tests, a reaction does occur after the transfusion is given (the unfavourable reaction often manifests itself in the form of a fever), an even more careful search must be made for any red cell antibody that might be the cause. A reaction after transfusion is not necessarily due to red cell antigen-antibody reactions. It could be caused by the presence of antibodies to the donor’s platelets or white cells. Transfusion reactions are a particular hazard for persons requiring multiple transfusions.

Organ transplants

The ABO antigens are widely distributed throughout the tissues of the body. Therefore, when organs such as kidneys are transplanted, most surgeons prefer to use organs that are matched to the recipient’s with respect to the ABO antigen system, although the occasional survival of a grafted ABO-incompatible kidney has occurred. The remaining red cell antigen systems are not relevant in organ transplantation.

Paternity testing


Exclusions of paternity on the ABO system
matings possible
O X O O A, B, AB
O X A O, A B, AB
O X B O, B A, AB
A X A O, A B, AB
A X B O, A, B, AB
B X B O, B A, AB


Blood groups and disease




Genetic and evolutionary significance of blood groups

Blood groups and genetic linkage



chromosome gene known
associated disease
1 Rh EL1 elliptocytosis
1 Radin Rh
1 Scianna Rh
1 Fy AMY1
4 MNSs Gc sclerotylosis
4 Gc Dombrock
6 Chido HLA
6 Rogers HLA
9 ABO AK1 nail-patella syndrome
19 Lewis C3
19 Lutheran secretor
Lutheran APOE
Lutheran PEPD
Lutheran DM myotonic dystrophy
Lutheran FHC familial hypercholesterolemia
Lutheran NF neurofibromatosis
19 H
X Xg hemophilia





Blood groups and population groups


