IMMUNOLOGY & BLOOD BANKING / IMMUNOHEMATOLOGY

IMMUNOLOGY & BLOOD BANKING / IMMUNOHEMATOLOGY

TERMS

  • Blood Banking: The procedures involved in collecting, storing, processing, and distributing blood for transfusion.

  • Immunology: The study of the molecules, cells, organs, and systems responsible for recognition and disposal of non-self substances. This includes the responses and interactions of body components, as well as the manipulation of the immune system to protect against or treat diseases.

  • Immunohematology: The study of antigen-antibody reactions and their effects on blood. This field includes blood transfusion medicine and blood banking.

  • Transfusion Reaction: A reaction of the body to a transfusion of blood that is incompatible with its own, which can range from mild symptoms (fever and hives) to severe outcomes (renal failure, shock, and death).

IMMUNOLOGY: ANTIGENS & ANTIBODIES

  • Antigen: A foreign substance that induces an immune response (i.e., antibody production) when introduced into a host.

  • Antibody: An immunoglobulin (a type of protein) produced in response to a foreign antigen that binds to it and initiates events to destroy the invader.

IMMUNOLOGY: IMMUNE RESPONSE

  • When exposed to disease-causing agents such as bacteria and viruses, foreign antigens are recognized by the host.

  • The host produces antibodies against these antigens, fighting off the disease, leading to immunity and the ability to remember the disease through antibodies.

  • Antibodies can persist for life, providing ongoing immunity to the previously encountered disease.

IMMUNOHEMATOLOGY: RBC ANTIGENS & ANTIBODIES

  • RBC Antigens: Red blood cells (RBCs) bear hundreds of chemicals on their surfaces known as antigens.

  • In a transfusion, if the recipient's immune system recognizes incoming RBC antigens as foreign due to existing antibodies, it can trigger a transfusion reaction, which may be fatal.

  • Antibodies are formed against antigens that are lacking in the individual; they develop because of the absence of an antigen in tandem with previous exposure to similar antigens.

MAJOR BLOOD ANTIGEN GROUPS

  • **Two Primary Ways to Expose to Foreign Blood:

    1. Transfusion: The recipient receives donor blood.

    2. Pregnancy: Exposure occurs when maternal blood interacts with fetal blood during delivery.

  • Major Antigen Systems:

    1. ABO System

    • Most crucial blood group antigen system, wherein individuals develop antibodies against antigens they lack in their plasma.

    • Antigens involved: A, B, or neither (O).

    1. Rh System

    • Considers the presence or absence of the D antigen on RBCs.

    • Rh Positive: Presence of D antigen.

    • Rh Negative: Absence of D antigen.

ABO BLOOD TYPES

  • ABO Types and Corresponding Antibodies:

    • Type A:

    • Antigen A present on RBC

    • Anti-B antibodies in plasma

    • Type B:

    • Antigen B present on RBC

    • Anti-A antibodies in plasma

    • Type AB:

    • Antigens A and B present on RBC

    • No antibodies in plasma

    • Type O:

    • Neither A nor B antigens present

    • Anti-A and anti-B antibodies in plasma

DEVELOPMENT OF ANTIBODIES

  • Individuals develop antibodies to foreign RBC antigens early in life, likely due to the presence of normal bacteria in the colon, which have antigen structures similar to A and B antigens.

  • Individuals inherit genes from their parents determining their blood type, affecting the antigens present on their RBCs (phenotype).

  • Antibodies are formed against antigens that an individual lacks, typically by age one.

BLOOD TRANSFUSION SAFETY

  • Careful matching is vital prior to blood transfusions:

    • The recipient must not have antibodies against the antigens present on the donor blood.

    • Example: A Type O recipient has antibodies against A & B; transfusing them with A or B blood can lead to a fatal reaction (acute hemolytic transfusion).

UNIVERSAL BLOOD TYPES

  • Universal Donor: Type O, as it has no A or B antigens on RBCs, preventing reactions with recipient antibodies.

  • Universal Recipient: Type AB, as it lacks anti-A or anti-B antibodies in plasma.

RH ANTIGEN SYSTEM

  • The Rh antigen, specifically the D antigen, is the second most important RBC antigen system.

  • Rh negative individuals can develop anti-D antibodies if they are exposed to Rh positive blood.

  • A Rh positive recipient can safely receive Rh positive or Rh negative blood, but Rh negative patients should receive Rh negative blood to prevent immunization reactions.

MAMA/BABY RH INCOMPATIBILITY

  1. First Pregnancy:

    • An Rh negative mother and an Rh positive father may have an Rh positive baby. During delivery, the mother is exposed to the baby's D antigen, leading to the production of anti-D antibodies over several weeks, which remain in circulation for life.

  2. Second Pregnancy:

    • If the next baby is Rh positive, the mother's anti-D antibodies can cross the placenta and attack the baby’s Rh positive RBCs, potentially causing hemolytic disease of the fetus and newborn (HDFN), which can be fatal.

PREVENTION OF HDFN

  • To prevent HDFN, Rh negative pregnant women should receive an RhIG (RhoGam) injection around 7 months of gestation and again after delivery if the baby is Rh positive.

  • RhIG binds to any Rh positive fetal cells in circulation, preventing the mother's immune system from recognizing them as foreign and producing anti-D antibodies.

BLOOD TYPING

  • Determining the antigen type on RBCs is done by testing with known antibodies. Clumping or agglutination indicates a positive result.

  • Forward Type Test: Searching for antigens on patient cells using manufactured reagent antibodies.

  • Reverse Type Test: Looking for antibodies in patient plasma using manufactured reagent RBCs (testing A and B types).

  • ABO Discrepancy: Occurs when forward results with patient cells do not match the reverse results from the patient’s plasma.

  • Situations that necessitate blood transfusions include: surgery, severe injuries, severe infections, liver disease impeding blood production, and anemia.

PRETRANSFUSION COMPATIBILITY TESTING

  • Involves the following steps:

    • Proper Identification of Recipient: This is the most critical step.

    • Type Check: ABO & Rh type of the recipient must be confirmed.

    • Donor Blood Check: ABO & Rh type of donor unit must be double-checked.

    • Antibody Screening: Assess for unexpected antibodies in recipient plasma.

    • Crossmatch: Ensure recipient plasma does not contain antibodies against the donor RBCs.

  • Autologous Transfusion: A patient may donate their blood for future transfusion, especially useful for those with specific antibodies.

OTHER BLOOD COMPONENTS

  • Whole Blood: Can be separated into RBCs, platelets, and fresh frozen plasma.

  • Packed Red Cells: Do not provide viable platelets or neutrophils.

  • Platelets: Essential for coagulation, containing some plasma with coagulation factors.

  • Fresh Frozen Plasma (FFP): Contains all coagulation factors at normal levels, free from red cells, leukocytes, and platelets. Rarely used due to risks of adverse reactions from leukocytes.

  • Each unit of whole blood is approximately 330 ml with a hematocrit of 50-70%. This is primarily used for substantial hemorrhage and symptomatic anemia, as well as for correcting known congenital or acquired coagulation factor deficiencies.