Examinations
Examinations
The ABO blood group system reflects the presence or absence of antigens on the surface of red blood cells and antibodies in the blood plasma.
Antigens on Red Blood Cells
- Red blood cells carry signaling molecules called antigens (agglutinogens) on their surface.
- Two main antigens, A and B, are attached to the red blood cell structure.
- Blood groups are determined by the presence or absence of these antigens:
- Group A (II): Contains antigen A on red blood cells.
- Group B (III): Contains antigen B on red blood cells.
- Group AB (IV): Contains both antigens A and B on red blood cells.
- Group O (I): Lacks both A and B antigens on red blood cells.
Antibodies in Plasma
- The body naturally produces antibodies against antigens not found on its own red blood cells. These antibodies are called agglutinins:
- People with Group A (II) blood have anti-B antibodies (beta-agglutinins) in their plasma.
- People with Group B (III) blood have anti-A antibodies (alpha-agglutinins) in their plasma.
- When the same antigen (on red blood cells) and antibody (in plasma) are present, they react, causing agglutination (clumping) of red blood cells. This reaction does not normally occur in the blood because antibodies against self-antigens are not produced.
Clinical Importance
The discovery of the ABO blood group system clarified why blood transfusions sometimes succeed and sometimes cause severe complications:
- If a person with Group A (II) blood (containing anti-B antibodies) receives Group B (III) blood, agglutination and destruction of red blood cells occur. This reaction can lead to fatal outcomes.
For this reason, blood groups must be compatible during transfusions to avoid serious complications.
Determining Blood Group
Blood group is determined by observing the presence or absence of red blood cell adhesion (agglutination) using serum containing standard antigens and antibodies.
- Avoid alcohol consumption 24 hours before the test.
- Refrain from eating for 2 hours before the test; you may drink plain, non-carbonated water. For infants, the test should be done before their next feeding.
- Avoid physical and emotional stress for 30 minutes prior to the test.
- Determination of blood group for medical purposes, including transfusions.
- Preparation for surgeries or other medical procedures requiring blood compatibility.
- Investigation of potential parent-child blood group compatibility.
- Screening for hemolytic disease of the newborn.
- General health assessment or documentation requirements.
Based on the results, a person's blood is categorized into one of four groups depending on the presence of antigens on red blood cells and antibodies in the blood plasma.
Blood Group | Antibodies in Plasma |
O (I) | α and β |
A (II) | β |
B (III) | α |
AB (IV) | None |