Question

A clean toothpick was dipped into a sample of human blood. The blood was then mixed with a drop of anti- A serum. No agglutination was observed. The blood type was

• A. A or B
• B. A or O
• C. B or O
• D. AB or B

Answer 1

Answer: (C)

B or O

There are four major blood groups determined by the presence or absence of two antigens A and B on the surface of red blood cells:

Group A – has only the A antigen on red cells (and B antibody in the plasma).

Group B – has only the B antigen on red cells (and A antibody in the plasma).

Group AB – has both A and B antigens on red cells (but neither A nor B antibody in the plasma).

Group O – has neither A nor B antigens on red cells (but both A and B antibody are in the plasma).

So, if a clean toothpick was dipped into a sample of human blood, mixed with a drop of anti- A serum and no agglutination was observed then the blood type was B or O because there are no A antigens on the surface of RBCs of B and O and present on RBCs of A and AB.

Therefore, the correct answer is option C.