Blood Groups and Transfusion

Blood Group Antigens and Antibodies

• Blood group antigens are proteins or polysaccharides on the surface of red blood cells, determined by genes and capable of stimulating antibody production.
• Antibodies are immunoglobulins in plasma that react with a specific antigen, produced against antigens not present on a patient's own red cells.
• There are two types of antibodies: naturally occurring (formed following exposure to environmental antigens similar to blood group antigens) and immune antibodies (formed following contact with blood group antigens).

ABO Blood Group System

• The ABO blood group system consists of polysaccharide antigens O, A, and B.
• Naturally-occurring antibodies are anti-A and anti-B.
• ABO grouping is performed by mixing patient cells with specific antisera and patient plasma with known red cells.
• ABO inheritance is determined by the genes encoding enzymes capable of synthesizing A and B antigens.
• The ABO blood group frequencies vary, but Group O is the universal donor and Group AB is the universal recipient.

Clinical Significance

• Recipients with anti-A or anti-B must not be transfused with donor cells expressing the corresponding antigen.
• Positive patient identification is essential to transfusion safety.

Rh Blood Group System

• The Rh ("Rhesus") blood group system consists of transmembrane proteins, with >50 antigens, and 'D' being the most immunogenic.
• Antibodies are immune only and form following exposure to RhD positive red cells through transfusion, pregnancy, or transplantation.
• RhD inheritance is determined by one gene (D/d) from each parent, with one copy of D making an individual D positive.
• RhD blood group frequencies vary, but it is essential to avoid giving RhD positive red cells to RhD negative recipients, especially women of child-bearing potential.

Haemolytic Disease of the Foetus and Newborn

• Consequences of haemolytic disease include foetal anaemia and neonatal jaundice, which can cause brain damage.
• Prevention involves administering anti-D immunoglobulin to RhD negative women to 'mop up' any RhD positive red cells entering maternal circulation.

Blood Transfusion

• Blood components include whole blood, red cells, platelets, fresh frozen plasma, plasma cryoprecipitate, clotting factor concentrates, immunoglobulins, and albumin.
• Ten steps are involved in transfusion, including pre-transfusion sampling, laboratory testing, and giving a transfusion.
• Positive patient identification is crucial before transfusing, and the patient's blood group and the donor unit's blood group must be confirmed.

Acute Haemolytic Reaction

• Onset is within minutes, causing intravascular haemolysis and a massive inflammatory reaction.
• Symptoms and signs include restlessness, fever, pain, tachycardia, nausea, and abnormal bleeding.
• Consequences can be severe, including shock, clotting abnormalities, renal failure, and death.