Question

Which blood group is known as the Universal Donor?

• A. A negative
• B. B negative
• C. O negative
• D. AB positive

Hint:

Remember the donor/recipient mnemonic:
O Negative ($O^-$): Universal Donor (No antigens to trigger immune attacks).
AB Positive ($AB^+$): Universal Recipient (No antibodies to attack foreign blood).

Answer 1

The Correct Option is C

Topic Explanation:
Blood grouping in humans is determined by the ABO system and the Rh factor system present on the surface of red blood cells (RBCs).
The presence or absence of specific antigens (A, B, and Rh factor) on RBC membranes determines blood compatibility during transfusions.

Step 1: Understanding the Question:
The question asks to identify which specific blood group can be safely donated to individuals of any blood group without causing agglutination or transfusion reactions.

Step 2: Key Formula or Approach:
Universal donor status requires the total absence of surface antigens on red blood cells:
1. ABO System: Blood group O has neither A nor B surface antigens.
2. Rh System: Rh-negative blood lacks the Rh (D) antigen.

Step 3: Detailed Explanation:

• Surface Antigens: Antigens A, B, and Rh (D) trigger immune responses in recipients who lack them.

• Antigen Composition of O negative ($O^-$):
- Lacks Antigen A
- Lacks Antigen B
- Lacks Rh (D) Antigen

• Compatibility Mechanism: Because $O^-$ RBCs carry no A, B, or Rh antigens on their membranes, the recipient's immune system will not recognize the transfused RBCs as foreign or produce antibodies against them.

• Contrast with AB positive ($AB^+$): $AB^+$ blood cells contain A, B, and Rh antigens, making $AB^+$ individuals universal recipients, not donors.

Step 4: Final Answer:
Because O negative ($O^-$) blood lacks all three primary antigens, it can be transfused into any recipient safety, making Option (C) the correct answer.