The ABO and Rhesus (Rh) blood group systems are the two most important and widely recognized systems for blood classification in humans. They are crucial in determining blood compatibility for transfusions, organ transplants, and pregnancy.
ABO Blood Group System
Discovered by Karl Landsteiner in 1901, the ABO blood group system classifies blood based on the presence or absence of two antigens—A and B—on the surface of red blood cells (RBCs). There are four main blood groups in the ABO system:
- Blood Group A
- Antigens: An antigen on the surface of RBCs.
- Antibodies: Anti-B antibodies in the plasma.
- Compatibility: Can receive blood from A and O blood groups and donate to A and AB groups.
- Blood Group B
- Antigens: B antigens on RBCs.
- Antibodies: Anti-A antibodies in the plasma.
- Compatibility: Can receive blood from B and O groups and donate to B and AB groups.
- Blood Group AB
- Antigens: Both A and B antigens on RBCs.
- Antibodies: No antibodies (anti-A or anti-B) in the plasma.
- Compatibility: Can receive blood from all ABO blood types (universal recipient) and can donate to AB only.
- Blood Group O
- Antigens: No A or B antigens on RBCs.
- Antibodies: Both anti-A and anti-B antibodies in the plasma.
- Compatibility: Can donate to all ABO blood groups (universal donor) and can only receive blood from O.
ABO Blood Group Compatibility Chart
|
Blood Type |
Can Receive Blood From | Can Donate Blood To |
|
A |
A, O |
A, AB |
|
B |
B, O |
B, AB |
|
AB |
A, B, AB, O (universal recipient) |
AB |
| O | O |
A, B, AB, O (universal donor) |
Rh Blood Group System
The Rhesus (Rh) blood group system, discovered by Karl Landsteiner and Alexander S. Wiener in 1940, involves the presence or absence of the Rh factor (also called D antigen) on the surface of red blood cells. This system adds a positive or negative distinction to the ABO blood groups, resulting in eight possible blood types (A+, A-, B+, B-, AB+, AB-, O+, O-).
Rh Status:
- Rh-positive (Rh+): If the D antigen is present on the RBCs, the blood is Rh-positive (e.g., A+, B+).
- Rh-negative (Rh-): If the D antigen is absent, the blood is Rh-negative (e.g., A-, O-).
Importance of Rh Factor
The Rh factor is critical in blood transfusions and pregnancy:
- Transfusions: Rh-negative individuals should not receive Rh-positive blood because their immune system may produce antibodies against the D antigen, leading to hemolytic reactions.
- Pregnancy: Rh incompatibility can occur if a Rh-negative mother carries a Rh-positive fetus. If fetal blood cells enter the mother’s bloodstream, her immune system may produce antibodies that attack the fetus’s Rh-positive red blood cells in future pregnancies, causing hemolytic disease of the newborn (HDN). This can be prevented by administering Rh immunoglobulin (RhoGAM) during and after pregnancy.
ABO and Rh Blood Types
The combination of ABO and Rh systems results in eight major blood types:
- A+
- A-
- B+
- B-
- AB+
- AB-
- O+
- O-
ABO and Rh Compatibility in Transfusions
- O-: Universal donor for all blood types, but can only receive from O-.
- AB+: Universal recipient, can receive from any blood type but can only donate to AB+.
- O+: Can donate to all positive blood types (A+, B+, AB+, O+) and receive from O+ or O-.
Blood Type Compatibility Chart for Transfusion:
|
Blood Type |
Can Receive From |
Can Donate To |
|
A+ |
A+, A-, O+, O- |
A+, AB+ |
|
A- |
A-, O- |
A+, A-, AB+, AB- |
|
B+ |
B+, B-, O+, O- |
B+, AB+ |
|
B- |
B-, O- |
B+, B-, AB+, AB- |
|
AB+ |
All (universal recipient) |
AB+ |
|
AB- |
A-, B-, AB-, O- |
AB+, AB- |
|
O+ |
O+, O- |
O+, A+, B+, AB+ |
|
O- |
O- |
All (universal donor) |
Purpose of Blood Group Testing:
- To identify ABO and Rh blood types.
- To ensure compatibility for blood transfusions.
- To assess Rh incompatibility during pregnancy.
- To identify the blood group for organ donation or receiving.
Blood Group Testing Methods
There are two main methods for determining blood type:
- Forward typing: Identifies the presence of A and B antigens on the surface of red blood cells.
- Reverse typing: Detects the presence of anti-A and anti-B antibodies in the blood plasma.
Procedure for Blood Group Testing
- Sample Collection
- A blood sample is collected via venipuncture, typically from the arm.
- The blood sample is placed in a test tube, which may contain an anticoagulant to prevent clotting.
- Forward Typing
- In forward typing, the laboratory checks for A and B antigens on red blood cells.
- The blood sample is mixed with two types of antibodies:
- Anti-A antibodies
- Anti-B antibodies
- Procedure:
- A drop of blood is placed in two separate wells or test tubes.
- Anti-A serum is added to one sample and Anti-B serum to the other.
- The samples are observed for agglutination (clumping).
- If clumping occurs with anti-A serum, A antigens are present (blood group A).
- If clumping occurs with anti-B serum, it indicates B antigens (blood group B).
- If clumping occurs with both, the blood group is AB.
- If no clumping occurs, the blood group is O.
- Reverse Typing
- Reverse typing checks for antibodies (anti-A or anti-B) in the blood plasma.
- The blood plasma is mixed with known type A and type B red blood cells:
- Plasma from the sample is mixed with red blood cells from blood groups A and B.
- Agglutination occurs if anti-A or anti-B antibodies are present in the plasma.
- If agglutination occurs with A cells, anti-A antibodies are present (blood type B).
- If agglutination occurs with B cells, anti-B antibodies are present (blood type A).
- If no agglutination occurs with either, the blood type is AB.
- If agglutination occurs with both, the blood type is O.
- Rh Typing
- Rh typing tests for the presence of the Rh factor (D antigen).
- A drop of blood is mixed with anti-D serum:
- If the blood agglutinates, the Rh factor indicates Rh-positive (Rh+) blood.
- If no clumping occurs, the blood is Rh-negative (Rh-).
Results Interpretation
The combination of forward and reverse typing results determine the ABO blood group, while Rh typing indicates whether the blood is Rh-positive or Rh-negative.
Example Results:
- Blood Group A+: A antigens on RBCs, anti-B antibodies in plasma, and Rh-positive.
- Blood Group O-: No A or B antigens on RBCs, anti-A and anti-B antibodies in plasma, and Rh-negative.
Detailed Steps in the Laboratory:
- Preparation:
- The blood sample is drawn and prepared on a slide or in test tubes.
- Anti-serum Application:
- Anti-A, anti-B, and anti-D reagents are added to separate wells or test tubes containing the blood sample.
- Observation for Agglutination:
- The blood sample is examined under a microscope or with the naked eye for clumping (agglutination).
- The presence or absence of agglutination helps determine the blood type.
- Record Results:
- Based on the reactions observed, the blood group is identified and recorded.
Accuracy and Considerations
- Blood group testing is generally accurate, but occasionally, repeat testing may be needed due to weak agglutination reactions or mixed-field reactions (e.g., from previous transfusions).
- Crossmatching may be done before transfusions to ensure donor and recipient blood compatibility.
Special Cases:
- Hemolytic Disease of the Newborn (HDN):
- If a Rh-negative mother carries a Rh-positive fetus, blood group testing helps monitor the potential risk of the mother producing antibodies against the fetus’s red blood cells. In such cases, Rho(D) immunoglobulin (RhoGAM) may be administered to prevent sensitization.
- Blood Transfusion:
- Before any transfusion, the recipient’s blood type is checked to avoid reactions caused by mismatched blood. Compatibility is determined by both ABO and Rh typing, with universal donor (O-) blood being used in emergencies when the recipient’s blood type is unknown.
- Organ Transplantation:
- Blood group testing is essential to ensure compatibility in organ transplants and reduce organ rejection risk.
Risks and Side Effects:
Blood group testing is generally safe. There are minimal risks associated with blood sample collection, such as:
- Mild discomfort or bruising at the site of venipuncture.
- Rarely, infection or excessive bleeding.