Question

Which blood group is known as the universal donor?

• A. A
• B. B
• C. AB
• D. O

Hint:

Remember:
- Universal Donor: O (no A or B antigens on RBCs)
- Universal Recipient: AB (no anti-A or anti-B antibodies in plasma)
Always consider the Rh factor (Rh-negative for universal donor, Rh-positive for universal recipient) for complete compatibility.

Answer 1

The Correct Option is D

Step 1: Understanding the Question:
The question asks to identify the human blood group that can be donated to individuals of any other ABO blood group without causing a major immune reaction, hence known as the "universal donor."

Step 3: Detailed Explanation:
The ABO blood group system is based on the presence or absence of specific antigens (A and B) on the surface of red blood cells (RBCs) and corresponding antibodies (anti-A and anti-B) in the plasma.
- Blood Group O: Individuals with blood group O have neither A nor B antigens on their RBCs. This absence of antigens means that their red blood cells will not be recognized as foreign by the recipient's immune system, regardless of the recipient's ABO blood group. However, Group O individuals have both anti-A and anti-B antibodies in their plasma. Therefore, Group O blood (specifically O negative for universal donor for Rh factor also) can be transfused to individuals of any other ABO blood group, making it the universal donor.
- Blood Group A: Has A antigens, anti-B antibodies.
- Blood Group B: Has B antigens, anti-A antibodies.
- Blood Group AB: Has both A and B antigens, no anti-A or anti-B antibodies. It is the universal recipient.

Step 4: Final Answer:
Blood group O is known as the universal donor.

Answer 2

This can be worked out by checking, for each blood group, whether transfusing it into a person of any other group would trigger an immune reaction (agglutination).

1. A: Blood group A carries A antigens on its red cells. If transfused into a person with group B blood (who carries anti-A antibodies in their plasma), those antibodies would attack the A antigens and cause clumping. So group A cannot be given to everyone.
2. B: Similarly, group B blood carries B antigens, which would be attacked by the anti-B antibodies present in a group A recipient's plasma, again causing a reaction. So group B is not universally safe either.
3. AB: Group AB red cells carry both A and B antigens, so transfusing this blood into a person with group A, B, or O blood would trigger a reaction with whichever antibody that recipient's plasma contains. Group AB is therefore the universal recipient, not donor, because a group AB person's own plasma lacks anti-A and anti-B antibodies and can safely accept blood from anyone.
4. O: Group O red cells carry neither A nor B antigens on their surface. Since there is nothing on the cell surface for a recipient's anti-A or anti-B antibodies to react against, group O blood can be given to a person of any ABO group without causing agglutination.

Only group O red cells lack both antigen types, which is exactly why they can be transfused into recipients of any blood group.

Therefore, the correct answer is O.