Blood Groups and Transfusions

Blood Groups

• RBC cell membrane contains agglutinogens (antigens)
• Blood plasma contains agglutinins (antibodies)
• Classification of blood groups (based on agglutinogens):
  • ABO system
  • Rh system
• ABO System: Classified by presence or absence of specific antigens (A, B)
  • Type O: Universal donor, no antigens, no clumping
  • Type A: Antigen A, antibody anti-B
  • Type B: Antigen B, antibody anti-A
  • Type AB: Antigens A & B, no antibodies, universal recipient, no clumping

Blood Transfusion Importance of ABO System

• The ABO system's importance lies in blood compatibility during transfusions
• Individuals must receive blood with compatible antigens to avoid harmful clumping reactions.

The Inheritance of A and B Antigens

• Blood type is genetically determined by two genes, one from each parent
• Possible genotypes for blood groups:
  • A: AA or AO
  • B: BB or BO
  • AB: AB
  • O: OO

Determining Blood Groups

• Blood grouping is done by adding agglutinins (anti-A and anti-B) to blood samples
• Agglutination (clumping) indicates the presence of a specific antigen
• Observing the presence or absence of clumping with each agglutinin determines blood type

Blood Group Incidences

• O+ is the most common blood type, followed by A+, B+, and AB+
• O- is the least common blood type, followed by A-, B-, and AB-

Rh System (Rhesus System)

• Rh factor: an antigen on red blood cells
• Rh positive individuals have the Rh antigen, Rh negative do not
• There are other Rh antigens (C, D, and E) but D is the most antigenic
• Rh incompatibility can lead to complications during blood transfusions or pregnancies

Hemolytic Disease of the Newborn (Erythroblastosis Fetalis)

• A condition where a mother's Rh antibodies attack the fetus's red blood cells
• Occurs when an Rh-negative mother carries an Rh-positive fetus
• The mother's immune system is sensitized, producing anti-Rh antibodies

Incidence of Hemolytic Disease of the Newborn

• Primarily affects the second or later pregnancies of Rh-negative mothers
• First pregnancy is typically unaffected, but subsequent pregnancies have increased risk

Pathogenesis of Hemolytic Disease of the Newborn

• Anti-Rh antibodies cross the placenta and attack the fetal red blood cells
• This leads to hemolysis (breakdown) of the red blood cells, releasing hemoglobin and causing jaundice

Treatment of Hemolytic Disease of the Newborn

• Exchange transfusion is used to remove the baby's Rh-positive blood and replace it with Rh-negative blood

Prevention of Hemolytic Disease of the Newborn

• Administering anti-D antibodies (RhoGAM) to Rh-negative mothers during pregnancy prevents sensitization

Blood Transfusion

• Indications:
  • Restore whole blood loss (>20%)
  • Restore specific blood components (e.g., RBCs, platelets, plasma proteins)
• Precautions:
  • Ensure donor and recipient blood compatibility (cross-matching)
  • Rh-negative individuals should not receive Rh-positive blood
  • Transfused blood must be free of infections (AIDS, hepatitis)
• Blood Transfusion Complications:
  • Transmission of infectious disease (AIDS, hepatitis, malaria)
  • Massive transfusion causing circulatory overload
  • Allergic reactions from incompatible blood components
  • Transfusion reactions occur when mismatched blood is infused (clumping and hemolysis)

Blood Lab Values (Packed Cell Volume, PCV, or Hematocrit, HCT)

• Ratio of packed red blood cells to total blood volume
• PCV = (Length of RBC column / Length of total blood column) x 100
• Normal values:
  • Males: 40-45%
  • Females: 37-40%
  • Newborns: 50-60%

Causes of High and Low Hematocrit

• High Hematocrit: Dehydration, burns, diarrhea, polycythemia vera, low oxygen tension (smoking, altitude)
• Low Hematocrit: Anemia, blood loss, bone marrow failure, hemolysis, leukemia

Blood Indices (MCV, MCH, MCHC)

• Used to classify types of anemia
• MCV: Mean Corpuscular Volume (size of RBCs)
• MCH: Mean Corpuscular Hemoglobin (amount of Hb in RBCs)
• MCHC: Mean Corpuscular Hemoglobin Concentration (concentration of Hb in RBCs)

Normal Values for Blood Indices

• MCV: 78-98 μm³
• MCH: 27-32 pg
• MCHC: 30-35 g/dL