ABO Blood Grouping
ABO இரத்த வகைப்பாடு
A simple mismatch in blood transfusion is not a medical error; it is a death sentence. Your RBC surface antigens are the biological ID cards that your immune system guards with lethal precision. Ignore this, and you trigger a massive hemolytic reaction.
The idea
ABO grouping is determined by the presence or absence of surface antigens A and B on the RBC membrane. Plasma contains corresponding antibodies, anti-A or anti-B, which are naturally occurring. This antigen-antibody interaction dictates the compatibility of blood types during transfusion. Group O lacks both antigens, making them universal donors, while AB lacks both antibodies, making them universal recipients.
Why it matters
It exists to prevent immune reactions (clumping) during blood transfusions by ensuring donor-recipient compatibility.
NEET lens
NEET focuses on the table of donor-recipient compatibility. Memorize the antigen-antibody combinations for all four groups. Watch for 'Universal Donor' vs 'Universal Recipient' traps; always verify if the question specifies ABO or Rh factor. Expect at least one matching-type question.
Clinical significance
Incompatible transfusion leads to acute hemolytic transfusion reaction. The recipient's antibodies attack the donor's RBCs, causing massive agglutination and hemolysis. This results in hemoglobinuria, renal failure, and potentially fatal shock.
Introduction
The ABO blood group system classifies human blood into four types (A, B, AB, O) based on the presence or absence of A and B antigens (agglutinogens) on RBC surfaces and corresponding antibodies (agglutinins) in plasma.
Core concept
Blood group A: antigen A on RBCs, antibody b (anti-B) in plasma. Blood group B: antigen B on RBCs, antibody a (anti-A) in plasma. Blood group AB: antigens A and B on RBCs, no antibodies — universal recipient. Blood group O: no antigens, both antibodies (a and b) — universal donor. Transfusion rule: donor antigens must not match recipient antibodies (agglutination/clumping → hemolysis → fatal). AB = universal recipient (no antibodies to react). O = universal donor (no antigens to be attacked). Genetics: IA, IB (codominant), i (recessive). IA IA or IA i = A. IB IB or IB i = B. IA IB = AB. ii = O.
Go deeper
Why does the body have pre-formed antibodies against blood groups it was never exposed to? Gut bacteria and environmental antigens share structural similarity to A and B antigens → immune system forms antibodies against them naturally in infancy. This is why ABO incompatibility reactions are immediate and severe (preformed IgM antibodies activate complement → massive hemolysis).
From Class 10
Before a blood transfusion, doctors check your blood group. The ABO system classifies blood into A, B, AB, and O based on antigens on red blood cells.