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Understanding Blood Types: Antigens and Blood Group Systems

Blood Group Systems: ABO and Rh

Blood type is determined by antigens (surface markers) on red blood cells, inherited from both parents. The two primary systems are ABO and Rh.

ABO Blood Group System

Based on presence/absence of A and B antigens:

  • Type A: A antigens only
  • Type B: B antigens only
  • Type AB: Both A and B antigens
  • Type O: Neither A nor B antigens

Rh Factor

Independent of ABO. Presence of Rh factor = Rh-positive (e.g., A+). Absence = Rh-negative (e.g., A-).

Blood Type Compatibility Table

Blood TypeAntigens Present
A+A, Rh
A-A
B+B, Rh
B-B
AB+A, B, Rh
AB-A, B
O+Rh
O-None

Clinical Significance

Transfusion Safety: ABO compatibility is critical. Incompatible transfusions cause life-threatening hemolytic reactions.

Rh Incompatibility in Pregnancy: An Rh-negative mother carrying an Rh-positive fetus can develop antibodies that attack fetal red cells, causing hemolytic disease of the newborn. Prevented by administering Rho(D) immune globulin (RhoGAM) during pregnancy and postpartum.

Blood typing is essential for safe transfusions and prenatal care.

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