Physiology · MU Pleven

BLOOD GROUPS. TRANSFUSION REACTIONS RESULTING FROM MISMATCHED BLOOD TYPES

Explains how the A and B antigens on red blood cells, and the matching antibodies in plasma, cause transfusion reactions when blood types are mismatched, including clumping and lysis. Outlines the laboratory steps of blood typing and then turns to the Rh system, covering how anti-Rh antibodies develop after exposure and how erythroblastosis fetalis arises in pregnancy. Ends with the neonatal treatment by blood replacement and the anti-D immunoglobulin used for prevention.

Inside: 1 section · 3 labelled pictures · 20 flashcards · 4 min

Topic 17 of 17 in the MU Pleven syllabus for Physiology (Medicine, Year 2). The free AceMed note covers it in 1 section, about 635 words (4 min of reading), with 20 flashcards.

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  1. BLOOD GROUPS. TRANSFUSION REACTIONS RESULTING FROM MISMATCHED BLOOD TYPES

BLOOD GROUPS. TRANSFUSION REACTIONS RESULTING FROM MISMATCHED BLOOD TYPES

Two antigens-type A and type B-occur on the surfaces of the red blood cells in a large proportion of human beings. It is these antigens (also called agglutinogens because they often cause blood cell agglutination) that cause most blood transfusion reactions.

Figure 35-1 shows the changing titers of the anti-A and anti-B agglutinins at different ages. A maximum titer is usually reached at 8 to 10 years of age, and this gradually declines throughout the remaining years of life.

The agglutinins are gamma globulins, as are almost all antibodies, and they are produced by the same bone marrow and lymph gland cells that produce antibodies to any other antigens. Most of them are IgM and IgG immunoglobulin molecules.

Blood typing:

  • Before giving a transfusion to a person, it is necessary to determine the blood type of the recipient's blood and the blood type of the donor blood so that the bloods can be appropriately matched.
  • This is called blood typing and blood matching, and these are performed in the following way:
  • The red blood cells are first separated from the plasma and diluted with saline.
  • One portion is then mixed with anti-A agglutinin and another portion with anti-B agglutinin.
  • After several minutes, the mixtures are observed under a microscope.
  • If the red blood cells have become clumped-that is, "agglutinated"-one knows that an antibody-antigen reaction has resulted.

Transfusions reactions resulting from mismatched blood types:

When bloods are mismatched so anti-A or anti-B plasma agglutinins are mixed with red blood cells containing A or B agglutinogens, the red blood cells agglutinate into clumps.

These clumps can plug small blood vessels throughout the circulatory system. In some cases, the antibodies induce lysis of red blood cells through activation of the complement system.

RH system

  • The Rh system is another important factor during blood transfusion.
  • In the Rh system, spontaneous occurrence of agglutinins almost never happens
  • Instead, the individual must first be exposed to an Rh antigen, usually through transfusion of blood or pregnancy.
  • When red blood cells containing Rh factor are injected into a person without the factor, anti-Rh agglutinins develop and reach a maximum concentration within about 2 to 4 months.
  • On multiple exposures to the Rh factor, the Rh-negative person eventually becomes strongly sensitized to it.
  • The mismatch of Rh factor blood leads to agglutination and hemolysis.

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