Human Blood Group Types
Blood Group Types – Human Blood
Overview of Blood Groups
Blood groups are classifications based on the presence or absence of specific antigens on the surface of red blood cells. These antigens trigger immune responses when foreign, making blood typing essential for safe transfusions, organ transplantation, and maternal–fetal medicine.
ABO System
The ABO system, discovered by Karl Landsteiner in 1900, is defined by two antigens (A and B) and their antibodies:
| Type | Antigens on RBCs | Antibodies in Plasma |
|---|---|---|
| O | None | Anti‑A, Anti‑B |
| A | A | Anti‑B |
| B | B | Anti‑A |
| AB | A and B | None |
Distribution varies by population: type O is most common worldwide, AB least common. Natural antibodies develop within months of birth due to environmental exposure to bacterial antigens.
Rh (Rhesus) System
The Rh system centers on the D antigen:
- Rh‑positive (Rh⁺): D antigen present (~85% of people).
- Rh‑negative (Rh⁻): D antigen absent.
Rh incompatibility between an Rh⁻ mother and Rh⁺ fetus can lead to hemolytic disease of the newborn if not managed with prophylactic anti‑D immunoglobulin.
Other Blood Group Systems
Beyond ABO and Rh, there are over 30 recognized systems, including:
- Kell: K and k antigens; highly immunogenic.
- Duffy: Fya and Fyb; malarial parasite receptor.
- Kidd: Jka and Jkb; implicated in delayed transfusion reactions.
- MN: M and N antigens on glycophorin.
Rare phenotypes like Bombay (hh) lack H antigen and type as O in routine tests but require special matching.
Compatibility & Transfusion
Safe transfusion requires matching both ABO and Rh types to avoid hemolysis. Universal donor and recipient types:
- Universal Donor: O⁻ (no A, B, or D antigens).
- Universal Recipient: AB⁺ (no anti‑A, anti‑B, and has D antigen).
Cross‑matching tests donor red cells against recipient plasma to detect unexpected antibodies.
Clinical Significance
- Transfusion Reactions: Acute hemolysis if incompatible.
- Hemolytic Disease of the Newborn: Rh and ABO incompatibilities.
- Organ Transplantation: Matching ABO and minor antigens reduces rejection.
- Epidemiology: Certain blood groups correlate with disease risk (e.g., gastric cancer, malaria).
Blood Typing Methods
Common laboratory methods include:
- Slide Agglutination: Mixing cells with anti‑A, anti‑B, anti‑D sera.
- Tube Testing: Incubation and centrifugation for more sensitive detection.
- Gel Card: Microtube hemagglutination assay.
- Automation: Solid‑phase adherence and microarray platforms.
Conclusion
Understanding blood group diversity is crucial for transfusion safety, prenatal care, and immunohematology. Advances in typing technology and expanded antigen matching continue to improve patient outcomes and reduce adverse reactions.