Blood Components, Antigens and ABO Typing

Main Components of Blood

• Red blood cells carry oxygen throughout the body.
• White blood cells are crucial for the immune system function.
• Plasma is a yellowish liquid containing proteins and salts.
• Platelets enable blood clotting.

Antigens

• Blood group depends on the antigens present on the surface of red blood cells.
• Antigens are molecules, either proteins or sugars.
• Antigen types and features vary among individuals due to minor genetic differences.
• Functions of antigens in blood:
  • Unique to the individual.
  • Transport of molecules into and out of cells.
  • Maintaining the structure of red blood cells.
  • Detecting unwanted cells that could cause illness.
  • Recognized as foreign if transfused into another individual.
  • Promotes agglutination of red cells if combined with antibody

Blood Groups and ABO Typing

• Scientists use ABO and Rh antigens to classify blood types.
• Blood typing, or ABO typing, identifies a person's blood type.
• Blood type is determined by the presence of certain protein antigens on the surface of red blood cells.
• The ABO blood group system classifies blood types based on antigens in red blood cells and antibodies in plasma.

ABO Blood Groups

• Group A: Red blood cells have A antigens, and the plasma contains anti-B antibodies; anti-B antibodies attack cells with B antigens if present.
• Group B: Red blood cells have B antigens, and the plasma contains anti-A antibodies; anti-A antibodies attack cells with A antigens if present.
• Group AB: Red blood cells have both A and B antigens, but the plasma has no anti-A or anti-B antibodies; individuals with AB type can receive any ABO blood type.
• Group O: Plasma contains both anti-A and anti-B antibodies, but red blood cells have no A or B antigens; individuals with any ABO blood type can receive Group O blood.

Rhesus (Rh) Factor

• Rh antigens are surface antigens on red blood cells; Rh (D) antigens are most important.
• Rh positive: Red cells express Rh antigens.
• Rh negative: Red cells do not express the Rh antigen; about 15% of the human population is Rh negative.

Universal Donor and Recipient

• O negative blood has no A, B, or RhD antigens.
• Group O negative blood is known as the universal donor because almost anyone can receive it.
• Rh-negative blood can be donated safely to individuals with either Rh-negative or Rh-positive blood.
• Rh-positive blood can only be donated to Rh-positive individuals.

Receiving Blood

• Doctors check blood compatibility before transfusion.
• Transfusing the wrong blood type can lead to life-threatening reactions and complications.
• Example: A person with group B antigens receiving blood with group A antigens will experience an immune response leading to rejection.
• Anti-A antibodies attack and destroy donor red blood cells that contain A antigens.
• Plasma attacks and destroys donor cells, potentially causing clumping or agglutination in blood vessels.
• Hemoglobin leaks out and can be toxic if cells break down.
• Other adverse effects include allergic reactions and anaphylaxis, with some reactions occurring immediately and others up to 28 days later.

Blood Types in Pregnancy

• A mother's blood type or Rh factor is not necessarily the same as the child's if parents have different blood types.
• If the mother is Rh-negative and the fetus is Rh-positive, the mother's immune system treats fetal cells as foreign.
• Fetal RBCs can cross the placenta and enter the mother's bloodstream, leading to sensitization and the development of anti-RhD antibodies.
• Antibodies cross the placenta and destroy the baby's red blood cells.
• Breakdown of these red blood cells produces bilirubin, causing the infant to become yellow; bilirubin levels may range from mild to dangerously high.
• Severe jaundice, brain damage, and hemolytic disease of the fetus and newborn may occur in some cases.
• Anti-D immunoglobulin administered at 28 and 34 weeks of pregnancy can prevent this, according to the World Health Organization (WHO).
• Blood testing during pregnancy assesses compatibility between the fetus and mother to predict possible risks.

Hemolytic Disease of the Newborn (HDN)

• If the baby is Rh-positive and the mother is Rh-negative, leakage of the baby's red blood cells into the mother's circulation often occurs during birth
• The leakage will cause the mother to create antibodies against the Rh antigen
• The created antibodies do not affect the first Rh+ born, but can cross the placenta and attack red cells of subsequent Rh+ fetuses.
• This destruction can cause hemolytic disease of the newborn, potentially resulting in fetal death.
• Anti-Injection is used at week 28 of pregnancy and within 72 hours of birth to prevent HDN