Physiology of blood group

2021-06-14 04:31 PM

When the wrong blood type is transfused, a transfusion reaction can occur, in which the donor's red blood cells are agglutinated.

On the membrane of human red blood cells, about 30 common antigens and hundreds of other rare antigens have been found. Most antigens are weak and are only used to study genetics and blood relations. However, there are two groups of antigens that are particularly important that can cause reactions in blood transfusions: the ABO and Rh antigen systems.

ABO . blood group system


In this system there are two types of antigens, A and B, located on the red blood cell membrane. In addition, there are two types of antibodies in plasma: anti-A (antibody a) and anti-B (antibody b). Antibody a is capable of agglutinating A antigen, and antibody b is capable of agglutinating B antigen.

People rely on the presence of A, B antigens on the red blood cell membrane to classify the ABO blood group system (table).

Table: ABO blood group system.

Blood group name

Ratio %

KN on red blood cell membrane

KT in plasma

White skin















A and B

There is no a and b




No A, B

a and b

The appearance of the A antigen, or B antigen, on the red blood cell membrane is regulated by genes.

Antibodies a and b are produced by antibody-producing cells. After birth, antibodies have not yet appeared in the plasma. It takes two to eight months for the baby's body to start producing antibodies (people with blood type A produce b antibodies, the same goes for other blood types). Antibody levels reach a maximum at the age of 8-10 years, after which it gradually decreases.

Blood transfusion reaction

When the wrong blood type is transfused, a transfusion reaction can occur, in which the donor's red blood cells are agglutinated, and very rarely, the recipient's red blood cells are agglutinated.

Red blood cells clump in clumps that can clog small blood vessels. Over the next few hours or days, haemolysis (rupturing of red blood cells) occurs. Sometimes immediately after a transfusion of the wrong blood type, haemolysis occurs immediately. One of the fatal consequences of a transfusion reaction is acute kidney failure.

Application in blood transfusion

Principles of blood transfusion:

General rule: Do not let antigens and corresponding antibodies meet. Thus, we are only allowed to transfuse blood from the same group.

Rule of minimum: When transfecting small amounts of blood (<200 ml), do not allow antigens on the donor's red blood cell membranes to meet the corresponding antibodies in the recipient's plasma. Blood can be transfused according to the classic blood transfusion scheme (figure).

When transferring blood from different groups (according to the blood transfusion scheme), the following rules must be observed:

Transmit only once.

The amount of blood to be transfused should not exceed 200 ml.

Slow transmission speed.

Try cross-reaction:

Before blood transfusion, cross-reactivity should be tested even if it is in the same group.

Donor red blood cells are mixed with recipient plasma on a slide. If no agglutination occurs, the recipient does not have antibodies to attack the donor red blood cells. The reaction between the donor plasma and the recipient red blood cells should also be checked, although it very rarely causes transfusion reactions.

Figure: Classical blood transfusion scheme.

The Rhesus (Rh) blood group system


There are 6 types of Rh antigens, they are denoted as C, D, E, c, d, e. A person with the C antigen does not have c and vice versa, the same is true for pairs Dd and Ee. Due to the mode of inheritance of these factors, each of us has 3 antigens belonging to 3 pairs of Cc, Dd, Ee (eg CDE; CdE; cdE; cDe...).

The D antigen is the most common and has the strongest antigenic activity, so those who carry the D antigen are called Rh-positive, those who do not carry the D antigen are called Rh-negative.

One thing to note is that in the Rh blood group system, anti-Rh antibodies are not naturally available in the blood. Antibodies are only produced in the blood of an Rh-negative person when this person receives an Rh-positive blood transfusion or when an Rh-negative mother carries an Rh-positive fetus. It is the result of the immune response.

Table: Rhesus blood group system.

Blood group name

DI antigen

Natural antibodies

Ratio %


Kinh (VN)


Rh +


Are not




Rh -

Are not

Are not




Complications due to Rh blood group incompatibility

In blood transfusion:

People with Rh-negative blood type receive Rh-positive blood transfusion, the first time almost no accidents. However, this person's body begins to produce anti-Rh antibodies. Antibody concentrations reach maximum after 2-4 months. If the person is subsequently transfused with Rh-positive blood, a complication may occur because the pre-existing anti-Rh antibodies, together with the anti-Rh antibodies produced by the second immune response, cause agglutination of Rh-positive red blood cells transmission in.

It should be noted that there are some Rh-negative individuals on their first Rh-positive blood donation who produce significant amounts of anti-Rh antibodies after 2-4 weeks. Thus, that antibody can cause agglutination of Rh-positive red blood cells still circulating in the blood. However, this late reaction is very gentle.

In obstetrics:

Happens to Rh-negative women who marry Rh-positive men. During pregnancy, the foetus can be Rh positive or negative. During the first Rh-positive pregnancy, a small amount of Rh-positive fatal blood enters the maternal circulation mainly at birth and stimulates the mother's body to produce anti-Rh antibodies. The child born this time is not affected at all. However, by the next pregnancy, anti-Rh antibodies enter the foetal circulation. If it is an Rh-positive pregnancy, anti-Rh antibodies can agglutinate the baby's red blood cells and cause miscarriage, stillbirth, or the baby being born with severe haemolytic jaundice.

In fact, during pregnancy, the foetal Rh factor is released into the foetal fluid and can diffuse into the maternal blood. However, during the first pregnancy (first exposure to the Rh antigen) the number of antibodies produced in the mother's body is not high enough to harm the fetus.

Figure: Obstetric complications in Rhesus blood group incompatibility