Question

A person with an unknown blood group under the ABO system, has suffered much blood loss in an accident and needs immediate blood transfusion. His one friend, who has a valid certificate of his own blood type, offers blood donation without delay. What would have been the type of blood group of the donor friend?
A. Type B
B. Type AB
C. Type O
D. Type A

Answer 1

Hint: Blood grouping is based on the type of antigen present on the RBCs of the donor and the antibodies present in the blood of the recipient. If a wrong blood type is administered to a patient, there will be rejection and the antibodies in the blood of the recipient will attack the RBCs of the donor and lead to hemolysis in the recipient.

Complete answer:
People have their blood group as:

BLOOD GROUP	GENOTYPE	ANTIGEN	ANTIBODY
A	AA/Ai	A	Anti B
B	BB/Bi	B	Anti A
AB	AB	A and B	No antibody
O	i i	No antigen.	Anti A and Anti B

Further, the positivity of the blood group depends on the presence of the D antigen on the surface of red blood cells.
The blood group AB has no antibodies. Thus, whatever blood is received won’t recognize the antigens. Thus, making it a universal receiver.
Since the blood group O has no antigen, in whichever blood type it is transfused to, there will be no rejection. This makes O negative blood type the universal donor as it doesn’t even have the D antigen.
Due to this reason, in emergency conditions, when there is no time to check for the blood type before transfusion, O negative blood type is transfused into the patient as it is the safest. Thus, the friend must be of O negative type so they need not check the blood type before transfusion.
So, the correct answer is option (C).

Note: ABO blood grouping is the most common system followed for blood transfusion.There is a rare blood group known as the Bombay blood group. The ABO blood grouping follows the Landsteiner's law. O positive on the other side should not be mistaken as a universal donor.