Correct Option: C

Red blood cell agglutination indicates clumping of RBC’s due to cold agglutinins which are most commonly IgM antibodies. These antibodies crosslink red cells, which causes overlapping (arrow) and loss of central pallor. The agglutination leads to reduction in red cell count, elevation in MCH and MCV as measured by automated instruments. Hemagglu-tination is when the particles involved are red blood cells. The agglutin is called hemagglutinin. In cross-matching, agglutination occurring when donor red blood cells and recipient’s serum or plasma are incubated together indicates that the donor blood is incompatible for that particular recipient.