Blood Groups Overview

Study Notes

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 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 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 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

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 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.

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 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.

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