Blood Groups 

Blood groups, also known as blood types, are classifications of blood based on the presence or absence of specific antigens on the surface of red blood cells (RBCs) and the antibodies present in the plasma. These antigens are inherited genetically and play a critical role in blood transfusions, organ transplantation, and understanding immune system responses.

1.0Blood Group System

• Blood Groups are determined by: Antigens on the surface of RBCs. Remember: Antigens can stimulate the immune system to produce antibodies. 
• About 20 blood group systems are known: v 
• [E.g.ABO System, Rh-System, MNS System, Kell System, Lewis System, Duffy, Lutheran, KIDD] 
• The two most common blood groups: v ABO Blood group System. 
• Rh (Rhesus)Blood group System.
• Karl Landsteiner is an Austrian scientist that: 
• Discovered the ABO Blood group system in 1901 
• Discovered Rh factor in 1930 along with Alexander S. Wiener 
• Nobel prize in Physiology/Medicine in 1930 

2.0ABO & Rh Blood group systems

ABO System

• Depends on : the presence of one or both or neither of the two blood antigens (A) and (B) on the surface of the RBC. 
• Four main ABO groups: A, B, AB, O v A and B blood groups are dominant over the O blood group. 
• A and B group genes are codominant. (Codominance: form of dominance in which the alleles of a gene pair in a heterozygote are fully expressed thereby resulting in offspring with a phenotype that is neither dominant nor recessive) 
• Each person has two copies of genes coding for their ABO blood group (one maternal and one paternal in origin) 
• Locus of alleles responsible for the ABO system is on the long arm of chromosome9.

 Rh System

• Depends on: the presence or absence of the Rhesus antigen (D) on the surface of RBC.  
• Presence of D (individual is Rh+ve) [85%] 
• Absence of D (individual is Rh–ve) [15%] Rhesus antigens: Dd, Cc, Ee 
• Locus of alleles responsible for Rh Factor is on the long arm of chromosome 1. 

Agglutinogens  

• It is Blood group Antigens (on RBCs membrane) (A&B).

Agglutinin (Antibody)

• It is The respective antibody to antigen 
• Or It is Antibodies in serum (In Plasma) 
• Agglutinins are immunoglobulins (IgM & IgG): Proteins which appear in the plasma or body fluids in response to administration of antigens.

Agglutination (Clotting)

• It is a Reaction (clumping) between Agglutinogens on RBC membrane and the respective AntiBody 
• In transfusion reaction If a person with blood group A was transfused with blood of group B which contains anti-A in plasma 
• The anti-A in plasma of recipient with blood group B will agglutinate the transfused cell (A). 
• The clumped cells plug (block) small blood vessels. 
• Sometimes causes hemolysis.

Genotype for each blood group

• A →AA , AO 
• B →BB , BO 
• AB →AB 
• O →OO

Agglutinin /Antibodies

• Examples of Agglutinins
• Anti-A & Anti-B antibodies.
• Naturally occurring antibodies. 
• Not present at birth, appear 2-8/12 weeks (2 to 8 months) after birth. 
• Triggered by A & B antigens in food and bacteria. 
• Are considered as IgM class.(large molecule) 
• Cannot cross placenta.

Anti-D antibodies

• NOT naturally-occurring antibodies. 
• Acquired by: 
• Transfusion of Rh-ve individuals with Rh+ve blood. 
• Rh-ve pregnancy with Rh+ve fetus. 
• Are considered as IgG classes. 
• Can cross placenta. 

3.0Comparing between Agglutinogens & Agglutinin 

Agglutination  

• If there is agglutination in the blood drop when Anti-A was used that means the patient's blood group is A. 
• Also: Anti-B → agglutination → blood group B. 
• If there is agglutination in the blood drop when we use both Anti-A and Anti-B that means the patient's blood group is AB. 
• If there isn’t agglutination in the drop patient blood when we use both Anti-A and Anti-B that means the patient's blood group is O.

• When the antigen and antibody are the same type, it can be dangerous and may lead to anemia.

4.0Importance of blood groups

• In blood transfusion. 
• In preventing hemolytic disease (Rh incompatibility between mother and fetus)  
• In paternity disputes (to determine the father) 
• In medicolegal cases 
• In knowing susceptibility to disease: 
• Group O: duodenal cancer. 
• Group A: carcinoma of stomach, pancreas & salivary glands. 

5.0Blood Transfusions(Donor and Recipients)

Blood group type of patient (recipient)

• People with blood group O are called “universal donors” people with blood group AB are called “universal recipients”. 

Blood group type of patient

• Type AB (contains agglutinogens A and B; agglutinates with both serum) 
• Type A (contains agglutinogen A; agglutinates with anti-A)
• Type B (contains agglutinogen B; agglutinates with anti-B)
• Type O (contains no agglutinogens; does not agglutinate with either serum)

Complications of Blood Transfusions

• Immune reaction: incompatible blood transfusions leading to immediate or delayed reaction, fever, hemolysis, allergic reaction. (appears within 10 to 15 minutes of transfusion) 
• Transmission of diseases: malaria, syphilis, viral hepatitis, and AIDs virus. 
• Iron overload: due to multi-transfusion in case of sickle cell anemia and thalassemia. 
• Acute kidney failure: (reaction to mismatched transfusions )

Hazards (Risks) of Mismatched Transfusions

• Agglutination

• Hemolysis 
• Fever 
• Allergic reaction 
• Acute renal shutdown 
• Renal vasoconstriction 
• Circulatory shock 
• Tubular blockage
• Sensitization 
• Thrombophlebitis

Rh incompatibility between mother and fetus

It is a condition that develops when a pregnant woman has Rh-negative blood and the baby in her womb has Rh-positive blood.

Mother is Rh –ve and the first baby is Rh +ve (has D antigen) :

At delivery: 

• Fetal Rh +ve RBC crosses to maternal blood. 
• The mother will develop anti-D after delivery. 
• First child escapes & is safe.
• If the mother was transfused before with Rh +ve blood before, the first child will be affected.

6.0Second fetus (baby): Rh +ve 

• Rh +ve: Antibody-D crosses the placenta from mom to baby and destroys fetal Rh +ve RBCs. 
• Outcome: Hemolytic disease of the newborn. 

7.0Hemolytic disease of newborn (Erythroblastosis fetalis)

• Hemolytic anemia: If severe: is treated with exchange transfusion: Replace baby’s blood with Rh –ve RBC (several times). 
• Hydrops fetalis: (death in utero)