BharatNotes What is Blood Groups and Rh Factor?
A blood group classifies blood according to inherited antigens on the red blood cell (RBC) surface. The two systems that matter most clinically are the ABO system and the Rh system.
In the ABO system, the A antigen and B antigen may be present individually, together, or absent — giving four groups: A, B, AB and O. Crucially, plasma contains naturally occurring antibodies against the antigens a person lacks. The Rh factor refers chiefly to the RhD antigen: if present, the person is Rh-positive; if absent, Rh-negative. Combining both systems yields eight common types (e.g., A+, O-, AB+).
Discovery and the Science
Karl Landsteiner discovered the ABO system in 1901, identifying antigens (A, B) and agglutinins (anti-A, anti-B); the AB group was added by von Decastello and Sturli in 1902. Landsteiner received the Nobel Prize in Physiology or Medicine in 1930. He and Alexander Wiener identified the Rh factor in 1940, naming it after the rhesus monkey (Macaca mulatta) used in the immunisation experiments; the antigen agglutinated roughly 85% of human samples tested.
ABO inheritance is a classic example of multiple alleles (Iᴬ, Iᴮ, i) with co-dominance (Iᴬ and Iᴮ) and dominance (both over i).
Antigens, Antibodies and Compatibility
| Group | Antigen on RBC | Antibody in plasma | Can donate RBCs to | Can receive RBCs from |
|---|---|---|---|---|
| A | A | anti-B | A, AB | A, O |
| B | B | anti-A | B, AB | B, O |
| AB | A and B | none | AB | A, B, AB, O |
| O | none | anti-A and anti-B | A, B, AB, O | O |
- Universal donor (RBCs): O-negative — no A, B or RhD antigens.
- Universal recipient: AB-positive — no anti-A/anti-B antibodies, plus RhD present.
Significance: Rh Incompatibility and Rare Types
Rh incompatibility arises when an Rh-negative mother carries an Rh-positive foetus. Mixing of foetal blood (usually at delivery) can sensitise the mother to produce anti-D antibodies; in a later Rh-positive pregnancy these cross the placenta and destroy foetal RBCs, causing haemolytic disease of the newborn (erythroblastosis fetalis). It is prevented by injecting Rh immunoglobulin (anti-D), and the first pregnancy is generally unaffected.
The Bombay phenotype (hh blood group) — first described in Mumbai in 1952 by Dr Y.M. Bhende — lacks the H antigen (the precursor for A and B). Such persons appear as group O on routine testing but can only receive blood from other Bombay-phenotype donors. It occurs in roughly 1 in 10,000 people in India versus about 1 in a million globally (figures as commonly reported in transfusion literature).
UPSC Angle
Focus on the logic of compatibility (antigen present → matching antibody must be absent in recipient), the universal donor/recipient pair, Rh incompatibility mechanism, and the inheritance genetics. These recur across Prelims Science & Technology and health questions.
