Blood Groups Overview

Blood Groups

• Blood groups are classified into four major types: A, B, AB, and O.
• This classification is based on the antigens present on red blood cell membranes.
• Red blood cells contain antigens called agglutinogens.
• Plasma contains specific antibodies called agglutinins.
• Agglutinins are gamma globulins.
• Typically, a person's blood does not contain an agglutinogen and its corresponding agglutinin to prevent agglutination.
• Example, if blood type is 'A', then the blood does not contain 'anti-A'.

Blood Groups: Specifics

• Blood group A (40% of population): Contains antigen A, plasma contains anti-B.
• Blood group B (10% of population): Contains antigen B, plasma contains anti-A.
• Blood group AB (5% of population): Contains both antigens A and B, plasma contains no antibodies (universal recipient).
• Blood group O (45% of population): Contains no antigens, plasma contains both anti-A and anti-B (universal donor).

Agglutination

• Agglutination of red blood cells (RBCs) occurs when the agglutinogen of the donor's blood reacts with the agglutinins of the recipient's blood.
• This reaction is caused by blood from a donor mixing with blood of a recipient.
• Group O blood contains no agglutinogens, so no agglutination occurs when given to others.
• Group AB blood contains no agglutinins, so no agglutination occurs when given to others.

Rh Factor

• Rh factor is an agglutinogen discovered in Rhesus monkeys' red blood cells.
• 85% of people have the Rh factor (Rh+ve), while 15% do not (Rh-ve).
• Rh-ve individuals usually do not have anti-Rh antibodies initially.
• Anti-Rh antibodies are formed in Rh-ve individuals only by two main mechanisms:
  • Blood transfusion from Rh+ve to Rh-ve individuals
  • Pregnancy of an Rh-ve female by an Rh+ve baby

Importance of Rh Factor

• In blood transfusion, if an Rh-ve person receives Rh+ve blood, anti-Rh antibodies develop in the plasma, leading to complications in subsequent transfusions.
• In pregnancies, if an Rh-ve mother carries an Rh+ve baby, fetal hemolysis might occur due to the mother developing anti-Rh antibodies. This can cause serious complications for the fetus, known as erythroblastosis fetalis.

Prevention and Treatment of Erythroblastosis Fetalis

• Prevention involves preventing an Rh-ve female from receiving Rh+ve blood (or marrying an Rh+ve male as much as possible), and administering Rh immunoglobulin (anti-D antibodies) within 48 hours of exposure to Rh+ve blood to neutralize maternal antigens.
• Treatment may involve repeated exchange blood transfusions in the newborn to remove the affected maternal blood and replace it with Rh-ve blood.

Clinical Significance

• Knowing blood type is important for:
  • Blood transfusions to avoid incompatibility.
  • Before marriage and during pregnancy to avoid erythroblastosis fetalis.
  • In cases of disputed paternity.

Blood Transfusion: Indications

• Decreased blood volume (e.g., hemorrhage).
• Severe anemia (hemoglobin levels below 40%).
• Hemorrhagic diseases (like hemophilia).
• Erythroblastosis fetalis.
• To supply white blood cells (leukocytes).
• To supply plasma proteins.

Precautions Before Blood Transfusion

• Blood should come from healthy donors.
• Blood should be freshly stored or recently stored (21 days max, kept at 4°C).
• Blood hemoglobin should be above 90%.
• ABO and Rh factor compatibility must be tested.
• Blood should be free from diseases such as malaria, syphilis, viral hepatitis, and AIDS.

Dangers of Blood Transfusion

• Incompatibility leading to agglutination, blocking capillaries, and causing ischemia or paralysis.
• Hemolytic jaundice and renal failure due to hemoglobin precipitation and renal tubule blockage.
• Release of toxic substances leading to vasoconstriction.
• Hypotension due to histamine liberation.
• Hyperkalemia.
• Tetany (due to low calcium level).
• Transfusion of excess blood leading to heart failure.
• Allergies.
• Transmission of diseases

Blood Typing Methods

• Sterilize the area to be pricked.
• Obtain blood sample.
• Apply anti-A, anti-B, and anti-D to different drops of the sample.
• Observe for agglutination (clumping) within one minute.

Results and Possibilities of Blood Typing

• Agglutination with anti-A serum = Type A blood
• Agglutination with anti-B serum = Type B blood
• Agglutination with anti-A and anti-B serum = Type AB blood
• No agglutination with any serum= Type O blood
• Agglutination with anti-D serum = Rh+ve blood
• No agglutination with anti-D serum = Rh-ve blood