blood grouping
Blood Groups and Blood Types
Introduction to Blood Types
Definition of Blood Type (Blood Group):
A blood type is a classification of blood based on the presence or absence of inherited antigenic substances on the surface of red blood cells (RBCs).
Blood is classified into different groups based on these antigens or agglutinogens.
ABO Blood Group System
Characteristics:
The ABO blood group system identifies blood types based on two glycolipid antigens: A and B.
Types are determined as follows:
Type O: No A or B antigens
Type A: A antigens present
Type B: B antigens present
Type AB: Both A and B antigens present
Agglutinins in ABO System
Antibodies in Blood Plasma:
Blood plasma contains antibodies (agglutinins) that react with non-self antigens.
Infants are born without these antibodies; they begin to appear at around 3–4 months due to exposure to ABO antigens found in bacteria, viruses, and environmental factors.
These absorbed antigens induce the body to form antibodies against non-self antigens not present on the infant's own RBCs.
Typically, these antibodies are IgM type and are too large to cross the placenta, preventing maternal-fetal incompatibility issues.
ABO Antigens and Antibodies Overview
Red Blood Cell Type | Antibodies in Plasma | Antigens in Red Blood Cell |
|---|---|---|
Group A | Anti-B | A antigen |
Group B | Anti-A | B antigen |
Group AB | None | A and B antigens |
Group O | Anti-A and Anti-B | None |
Agglutination Reaction
Process of Agglutination:
Occurs if a recipient receives the wrong blood type.
When foreign antigens are encountered by the immune system, agglutination (clumping) occurs due to antibodies binding to these antigens, leading to potential blockage of blood vessels and can cause death.
Examples of Agglutination
Type A Blood with Anti-B Antibody:
No match, no agglutination occurs.
Type B Blood with Anti-A Antibody:
Match, agglutination occurs.
Blood Group Compatibility
Blood Group | Blood Groups | Antigens | Antibodies | Can donate RBC to | Can receive RBC from |
|---|---|---|---|---|---|
AB | A and B | None | AB | AB | AB, A, B, O |
A | A | A | Anti-B | A and AB | A and O |
B | B | B | Anti-A | B and AB | B and O |
O | None | None | Anti-A and Anti-B | AB, A, B, O |
Rh Factor
Definition:
In addition to the ABO antigens, human red cells contain an Rh antigen (Rh factor) with several varieties (C, D, E, c, d, e).
The D antigen is the most common and potent.
Individuals with the D antigen are termed Rh positive (Rh+), while those without it are Rh negative (Rh-).
There are no naturally occurring antibodies against the Rh (D) antigen in the body fluids; it is present only on red blood cells.
Clinical Significance of Rh Factor
Immune Response in Rh Negative Individuals:
During Transfusions:
Rh-ve persons can develop anti-Rh antibodies after exposure to Rh+ blood.
Sensitization occurs during the first Rh+ transfusion without immediate reaction; subsequent transfusions lead to severe agglutination.
In Pregnancy:
A common scenario occurs when an Rh-ve mother carries an Rh+ fetus.
At delivery, Rh+ fetal blood may enter the maternal circulation, stimulating anti-Rh antibody production.
While the first-born may be unaffected, subsequent pregnancies can lead to hemolytic disease of the newborn (HDN) or erythroblastosis fetalis due to maternal antibodies crossing the placenta.
Prevention and Treatment of Hemolytic Disease of the Newborn
Prevention:
To prevent HDN, Rh-ve mothers can receive Rho(D) immune globulin injections post-delivery or after miscarriage.
This treatment clears Rh antigens from maternal circulation, preventing antibody formation.
Universal Donor and Recipient Concept
Universal Donor (Type O):
Type O individuals lack A and B antigens on RBCs, allowing their blood to be given to all blood types.
Universal Recipient (Type AB):
Type AB individuals have no circulating agglutinins, permitting them to receive blood from any ABO type.
ABO Incompatibility in Hemolytic Disease of the Newborn
Reason Why HDN is Rare with ABO Incompatibility:
ABO incompatibility seldom causes HDN because the anti-A and anti-B antibodies (IgM type) are too large to cross the placenta.
Blood Donation and Fractionation
Blood Bank Practices:
To maximize the benefits and extend blood shelf-life, blood banks fractionate whole blood into products like packed RBCs, plasma, and platelets.
For packed RBC transfusions, O Rh negative blood is ideal as a universal donor, while AB Rh positive is the universal recipient.
In plasma transfusions, O plasma can only be given to O recipients due to its anti-A and anti-B antibodies, while AB plasma is safe for all ABO groups as it lacks these antibodies.
Summary
Understanding blood types, antigens, and compatibility is critical for blood transfusions, managing Rh factor challenges in pregnancy, and ensuring safe blood donation practices.