Blood Physiology and Types

Blood Physiology

• Blood transfusions, when the patient has antibodies to the donor's antigens, can cause red blood cell agglutination and lysis.
• Severe transfusion reactions can be fatal.
• Some transfusion reactions are well-tolerated and beneficial.
• Transfusions led to the discovery of red blood cell antigens and cross-matching techniques.
• Over 30 common red blood cell antigens exist, with many rare ones.
• Patient and donor blood compatibility is crucial; antigens and antibodies need matching.
• ABO and Rh blood typing systems are essential for blood transfusions.

Blood Types

• Surface antigens (like ABO and Rh) determine blood type.
• ABO antigens are found on red blood cells and dictate blood types (A, B, AB, O)
• Each blood type has corresponding antibodies.
• A blood type has anti-B antibodies.
• B blood type has anti-A antibodies.
• AB blood type has no antibodies, and is a universal recipient.
• O blood type has both anti-A and anti-B, and is a universal donor.

Early Transfusions

• Early transfusions led to critical medical discoveries regarding blood transfer.
• Medical professionals realized that blood transfusions were not as straightforward as initially anticipated.
• The need to match donor and recipient blood types became evident.

Blood Typing

• Blood typing involves testing blood to identify specific antigens.
• If blood contains antigen A and you add Anti-A then agglutination occurs.
• If blood contains antigen B and you add Anti-B then agglutination occurs.
• If blood contains both antigens A & B and you add both Anti-A & Anti-B, then agglutination occurs.
• If the blood does not agglutinate with either, then the blood type is O.

Rh Antigens

• Rh factors are another important consideration in blood transfusions.
• Requires prior exposure to incompatible blood for a reaction to occur.
• Six common Rh antigens (C, D, E, c, d, e) exist.
• The D antigen is particularly important and frequent.
• 85% of people are Rh+.
• C & E can also cause mild transfusion reactions.
• ABO reactions are immediate, while Rh reactions are delayed.

Anti-Rh Transfusion Reactions

• Rh+ blood into Rh- recipients can cause a weaker delayed reaction, which includes sensitization.
• Sensitization occurs when the immune system is activated against Rh+ cells, by the exposure to Rh+ blood.
• 50% of Rh- are sensitized by a first exposure, and 20% by subsequent.
• Rh matching is important to prevent immunization.

Hemolytic Disease of the Newborn (Erythroblastosis Fetalis)

• In Rh incompatibility, maternal antibodies can cross the placenta and attack fetal red blood cells.
• This usually doesn't occur in first pregnancies
• This condition is more worrisome in second pregnancies and subsequent pregnancies.
• Increased severity with subsequent pregnancies.
• Immunization can occur due to fetal-maternal bleeding during delivery.

Hemolytic Disease Treatment

• Repetitive removal and replacement of Rh+ blood with Rh- blood is one treatment approach.
• Maternal antibodies can disappear after one to two months, lessening the risks.

Hemolytic Disease Prevention

• Exogenous anti-D antibodies can be given to the mother in late pregnancy and after birth, binding to fetal Rh+ cells, preventing an immune response.

Blood Component Transfusion

• Single donation amounts to 450 ml of blood.
• Blood is processed into components like packed red blood cells, plasma, platelets, and white blood cells.
• Packed red blood cells are stored for 30-40 days.
• Plasma (clotting factors) is stored frozen.
• Platelets are stored for 8-10 days.
• White blood cells are less commonly used.

Transfusion Reactions

• Mismatched blood can lead to transfusion reactions.
• Recipient antibodies reacting against donor antigens causes agglutination.
• Reactions can be immediate or delayed.
• Reactions can include fever, chills, shortness of breath, shock, and renal shutdown.
• Macrophages process the released hemoglobin to bilirubin, which can cause jaundice if there is high quantities and/or impaired liver function.

Acute Renal Failure After Transfusion Reaction

• Products of hemolysis can cause powerful renal vasoconstriction.
• Immune-mediated circulatory shock is possible.
• Free hemoglobin leaking into tubules can block them due to high quantities.
• Hemodialysis may be necessary.