Antigenic composition and classification
The Rhesus (Rh) system is a complex consisting of six main antigens: D, d, C, c, E, e. The strongest and most clinically significant is antigen D, as it possesses the most pronounced antigenic properties.
Depending on the presence of antigen D, all people are divided into two categories:
- Rh-positive (Rh+): the overwhelming majority of the population (about 85%), whose erythrocytes contain antigen D.
- Rh-negative (Rh-): a smaller part of the population (15%) in whom this antigen is absent.
Sensitization and immune conflict
The most important feature of the Rh system is that normally a person does not have pre-formed antibodies to the Rhesus factor. They begin to be produced in the body of an Rh-negative person only when a foreign Rh antigen enters it. This immunization process is called sensitization.
Antibody production occurs in two main situations:
- During the transfusion of Rh-positive donor blood to an Rh-negative recipient.
- During pregnancy, if an Rh-negative woman is carrying an Rh-positive fetus.
Clinical consequences of incompatibility
If a sensitized person (in whose body antibodies have already formed) is re-exposed to antigen D, a severe immune conflict develops.
- In the recipient: an acute transfusion reaction occurs, associated with the destruction of erythrocytes. The condition can deteriorate rapidly up to the development of transfusion shock.
- In pregnant women: Rhesus incompatibility arises between the mother and the fetus. This leads to intrauterine fetal death, spontaneous miscarriage, or the birth of a child with severe hemolytic disease.
Features and hidden risks of transfusion
In surgery and transfusiology, there is a strict rule: it is necessary to use blood that is strictly identical in Rhesus factor. Before any blood transfusion, a Rhesus compatibility test is mandatory. It is important to remember several critical nuances:
- The "insidiousness" of the first transfusion: if the recipient was not previously sensitized, the first transfusion of Rh+ blood to an Rh-negative patient may pass without a visible incompatibility reaction. However, the body will initiate antibody production, and any subsequent administration of Rh+ blood will lead to a severe reaction.
- The danger of weak antigens: the transfusion of Rh-negative blood to Rh-positive recipients is not always safe. Individuals with Rh- blood may carry other, weaker antigens of the system (for example, C or E). The entry of such antigens into the blood of an Rh+ recipient causes reverse sensitization and creates a high risk of post-transfusion complications.
Briefly: answers to topical questions
What clinical forms are distinguished in hemolytic disease of the newborn during Rhesus conflict?
Hemolytic disease of the newborn has several clinical forms that differ in the severity of manifestations.
- Hemolytic anemia without jaundice and hydrops is the mildest form, manifested by skin pallor and a decreased hemoglobin level.
- Iteric form — accompanied by the formation of unconjugated bilirubin, which can cross the blood-brain barrier and cause a severe complication in the form of kernicterus.
- Edematous form (fetal hydrops) — characterized by the development of edema, pastosity of subcutaneous tissue, ascites, or generalized edema.
How are individual compatibility tests for the donor and recipient blood performed regarding the Rhesus factor?
The individual Rhesus compatibility test is performed using 33% polyglucin (dextran).
- Before transfusion, the compatibility test is performed with blood from each vial.
- Transfusion is allowed only if the blood group and Rhesus type match and there is no agglutination in the compatibility tests.
- At the beginning of the transfusion, a biological compatibility test is additionally performed; the volume of the first 15–20 ml of administration is specified in the source.
Rule of the first encounter: the first contact of an Rh-negative organism with a foreign antigen passes without symptoms, but leaves a "memory" (antibodies). The second encounter always turns into an acute conflict.
Class and exam questions
Normally, there are no antibodies to the Rhesus factor in the plasma. During the first contact, the incompatibility reaction may be absent, as the body needs time to produce antibodies (latent sensitization occurs).
Normally, there are no antibodies to the Rhesus factor in the plasma. During the first contact, the incompatibility reaction may be absent, as the body needs time to produce antibodies (latent sensitization occurs).
What are the risks of transfusing Rh-negative blood to an Rh-positive recipient?
Donor Rh-negative blood may contain other, weaker antigens of the Rh system. An Rh-positive recipient may develop antibodies against them, which will provoke complications during subsequent blood transfusions.
What are the consequences of an immune conflict for a pregnant woman?
When Rhesus incompatibility develops, the mother's antibodies destroy the blood of the Rh-positive fetus, which can lead to fetal death, miscarriage, or the birth of a child with hemolytic disease.
What else to study on this topic
- Methodology for conducting the clinical Rhesus compatibility test
- Pathogenesis and stages of transfusion shock
- Immunogenicity of weak antigens of the Rh system (C, c, E, e)
- Prevention of Rhesus conflict during pregnancy
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