Immunohematology, blood group typing, disease and transfusion

Table of Contents

Introduction to Immunohematology

Immunohematology is a specialized field that combines principles from immunology and hematology to understand the interactions between blood components and the immune system. It primarily focuses on blood group systems and their implications for blood transfusion and related medical conditions.

Blood is composed of four main components:

Plasma (55% of blood): The liquid portion that contains water, electrolytes, proteins (like albumin, fibrinogen, and antibodies), nutrients, hormones, and waste products.
Red Blood Cells (RBCs) (45% of blood): Also called erythrocytes, these cells carry oxygen from the lungs to the body’s tissues and bring carbon dioxide back to the lungs.
White Blood Cells (WBCs): Also known as leukocytes, these cells are involved in the immune response and help protect the body from infections and foreign invaders.
Platelets (Thrombocytes): These small cell fragments help with blood clotting to stop bleeding when blood vessels are injured.

Understanding the immune system, which is the body’s defense mechanism is fundamental to immunohematology, as it governs how the body responds to foreign antigens, including those present on blood cells.

In context of immunohematology two important key Components are :

Antibodies (Immunoglobulins): Proteins produced by B cells that specifically bind to antigens.
Antigens: Molecules or substances that are recognized by the immune system as foreign. In blood immunohematology, these are often found on the surface of red blood cells and other blood components.

Each species of animal including human, has certain antigen unique to that species which are usually present on the rd cell membrane of the member of that species.

Even within the member of the same species there can be antigen found on the surface of the blood cells of some, that are not from on the red blood cells of other. And some antigen are more common then other.

Blood Groups and Antigens

Based on the presence or absence of the of those antigen the red blood cells can be caterorised in different groups. These antigens are inherited and can affect transfusion compatibility and immune responses.

Hundreds of known RBCs antigen have been organized into 30 blood group system. Some of the more common blood group system are- ABO, Rh, Kidd, MNS, Lewis, Kell and Duffy.

ABO Blood Group System:

First introduced by Karl Landsteiner (1900)
The ABO system is determined by the presence of A, B and O antigen on the surface of red blood cells. The inheritance of these antigens follows Mendelian genetics.
There are 4 phenotype in the ABO blood group system: A, B, AB, and O.

Each group has two gene for any train. It can have following combination fof allele aor genotype –

AA, AO for group A
BB or BO for Group B
OO for group O
AB for AB

Landsteiner Rule

if A or B antigen is not present on the surface of the red blood cells the corresponding antibody will be found in the serum.

Example –

A person lacking the A antigen on the surface of their RBCs, will have anti A antibody in their plasma or serum.

This occure only in ABO system

Type A: Has A antigens and anti-B antibodies.
Type B: Has B antigens and anti-A antibodies.
Type AB: Has both A and B antigens and no anti-A or anti-B antibodies.
Type O: Has no A or B antigens and both anti-A and anti-B antibodies.

Rh Blood Group System:

The Rh system includes several antigens, but the D antigen is the most clinically significant. Rh-positive individuals have the D antigen, while Rh-negative individuals do not.
Clinical Significance: The Rh status is crucial in pregnancy and transfusion settings. Rh incompatibility between mother and fetus can lead to hemolytic disease of the newborn (HDN).

Other Blood Group Systems:

Kell, Duffy, Kidd, MNSs Systems: These are additional systems with their own antigens and clinical significance. For example, the Kell system includes antigens that can be implicated in transfusion reactions and hemolytic disease.

From this chart we can see that

Blood group AB+ positive can receive from all the ABO type. It is Universal recipient.
Blood group O- can donate all the ABO group and are called universal Donor.

Note – This chart is for only RBCs transfer not whole blood.

Figure – Plasma Compatibility ( for plasma O is universal recipient and AB is universal donor.)

Blood Typing and Crossmatching

A. Techniques for Blood Typing

Forward Typing (Reagent Typing):
- This test identifies the blood group by mixing a patient’s red blood cells with known anti-A and anti-B reagents. The presence or absence of agglutination (clumping) determines the ABO blood type.
- Results Interpretation:
  - Agglutination with anti-A reagent indicates Type A blood.
  - Agglutination with anti-B reagent indicates Type B blood.
  - Agglutination with both indicates Type AB blood.
  - No agglutination with either indicates Type O blood.
Reverse Typing (Serum Typing): This test involves mixing the patient’s serum (containing antibodies) with known A and B red blood cells to detect the presence of anti-A and anti-B antibodies.
- Results Interpretation:
  - Presence of anti-A antibodies reacts with Type A red blood cells.
  - Presence of anti-B antibodies reacts with Type B red blood cells.
  - The pattern of agglutination helps confirm the blood group.

B. Crossmatching Procedures

Major Crossmatch: To ensure that the recipient’s antibodies do not react with the donor’s red blood cells.
- Mix a sample of the recipient’s serum with donor red blood cells. If no agglutination occurs, the blood is considered compatible for transfusion.
Minor Crossmatch: To check if the donor’s plasma antibodies react with the recipient’s red blood cells.
- Mix a sample of donor plasma with recipient red blood cells. This test is less commonly performed today due to advances in blood typing technology but is useful in certain complex cases.

C. Importance in Preventing Transfusion Reactions

Compatibility Testing: Ensures that blood transfusions are safe by preventing hemolytic reactions caused by incompatible blood.
Reduced Risk: Proper blood typing and crossmatching significantly decrease the risk of transfusion-related complications, ensuring a higher safety margin for patients.

Blood Transfusion and Immunohematology

If blood containing foreign antigen on the surface of red blood cell is transferred into recipient whose red blood cells do not have that antigen, the recipient form antibody to that particular antigen.

Once those antibody are present in the recipients plasma future transfusion of RBCs with that antigen on their surface can cause a significant, possibly even life threatening, adverse immune response termed a transfusion reaction.

The primary goal of blood transfusion in immunohematology is to ensure that the blood transfused does not provoke an immune reaction that could harm the recipient. Key considerations include:

ABO Compatibility: Transfusions should ideally be ABO-compatible. For example, type A blood should only be given to individuals with type A or AB blood types, and type O can be given to anyone, as it is considered the universal donor.
Rh Compatibility: Rh-negative individuals should not receive Rh-positive blood unless in emergency situations, but Rh-negative blood is preferable for women of childbearing age to prevent Rh sensitization.
Blood Components: Various blood components may be transfused depending on the clinical need:
- Whole Blood: Rarely used, as components are typically separated for more targeted therapies.
- Packed Red Blood Cells (PRBCs): Primarily used for treating anemia or blood loss.
- Platelets: Used for treating thrombocytopenia (low platelet count).
- Plasma and Cryoprecipitate: Contain clotting factors and are used for bleeding disorders.

Types of Transfusion Reactions

Hemolytic Reactions:
- Acute Hemolytic Reaction: Occurs immediately or within hours of transfusion due to ABO incompatibility. Symptoms include fever, chills, back pain, and hemoglobinuria.
- Delayed Hemolytic Reaction: Occurs days to weeks after transfusion, often due to Rh or other minor antigen incompatibilities. Symptoms can include anemia and jaundice.
Allergic Reactions:
- Mild Allergic Reactions: Include symptoms like itching, rash, and urticaria. These are usually manageable with antihistamines.
- Severe Allergic Reactions (Anaphylaxis): Rare but severe reactions that can cause difficulty breathing and hypotension. Immediate treatment with epinephrine and supportive care is required.
Febrile Non-Hemolytic Transfusion Reaction (FNHTR):
- Cause: Often caused by cytokines released from leukocytes in the transfused blood.
- Symptoms: Fever, chills, and sometimes headache. It is generally managed with antipyretics and is usually self-limiting.
Transfusion-Related Acute Lung Injury (TRALI):
- Cause: Associated with antibodies in donor plasma that react with recipient leukocytes, leading to lung inflammation.
- Symptoms: Sudden onset of respiratory distress and hypoxemia. Requires prompt recognition and supportive respiratory care.

Condition /Disease due to blood incompatibility

Hemaolytic anemica of newborn

Hemolytic anemia of the newborn (also known as neonatal hemolytic disease) occurs when a newborn’s red blood cells are destroyed faster than they can be produced, leading to anemia (a low red blood cell count). It is commonly caused by an immune reaction where antibodies from the mother attack the baby’s red blood cells.

The two main causes are:

Rh Incompatibility: This occurs when the mother is Rh-negative and the baby is Rh-positive. The mother’s immune system may produce antibodies against the baby’s Rh-positive red blood cells, leading to their destruction.
ABO Incompatibility: This occurs when the mother and baby have different blood types, most often when the mother is type O and the baby is type A or B. The mother may produce antibodies against the baby’s red blood cells, leading to their breakdown.

Symptoms:

Jaundice (yellowing of the skin and eyes)
Pale skin
Enlarged liver or spleen
Severe cases may lead to kernicterus (brain damage caused by high bilirubin levels).

Treatment:

Phototherapy (using light to break down bilirubin)
Exchange transfusion (in severe cases, to replace the baby’s blood with fresh blood)
Intravenous immunoglobulin (IVIG) can also be used to treat severe cases of ABO incompatibility.
Preventive measures, such as administering Rh immunoglobulin (RhoGAM) to Rh-negative mothers during pregnancy and after delivery, can help prevent Rh incompatibility.

Autoimmune hemolytic anemia

Autoimmune Hemolytic Anemia (AIHA) is a condition where the body’s immune system mistakenly attacks and destroys its own red blood cells, leading to anemia (a shortage of red blood cells). This can result in a reduced ability to carry oxygen to tissues, causing symptoms like fatigue, pallor, and shortness of breath.

Types of Autoimmune Hemolytic Anemia:

Warm Antibody AIHA:
- The most common form, where antibodies (usually IgG) attack red blood cells at normal body temperature (37°C).
- It is often associated with conditions like autoimmune diseases (e.g., lupus), infections, or certain cancers.
Cold Agglutinin AIHA:
- In this form, antibodies (usually IgM) attack red blood cells at lower temperatures, typically below body temperature.
- This is often triggered by infections (like Mycoplasma pneumonia or Epstein-Barr virus) or can be idiopathic (of unknown cause).
Mixed AIHA:
- A combination of both warm and cold antibody reactions.

Symptoms:

Fatigue
Jaundice (yellowing of the skin and eyes)
Dark urine (due to the breakdown of red blood cells)
Pale skin
Enlarged spleen (splenomegaly)
Shortness of breath and dizziness

Causes:

AIHA can be primary (with no underlying cause) or secondary to other conditions like:

Autoimmune diseases (e.g., lupus, rheumatoid arthritis)
Infections
Certain medications (e.g., penicillin, quinine)
Lymphoproliferative disorders (e.g., lymphoma, leukemia)

Diagnosis:

Blood tests showing anemia, elevated reticulocyte count, and the presence of antibodies or complement on red blood cells (via the Direct Antiglobulin Test (DAT) or Coombs test).
Peripheral blood smear showing signs of hemolysis, such as spherocytes (abnormally shaped red blood cells).