Paul Bunnell Test is used for detecting heterophil antibodies in infectious mononucleosis. This test uses sheep RBCs that are specially prepared. When these clump or aggregates, then they are put in blood samples of patients with heterophile antibodies. The test is based on the principle of presence of sheep agglutinins in the sera of infectious mononucleosis patents, which are absorbed by OX ready cells but not by guinea pig kidney extract. It is performed to confirm Infectious Mononucleosis and also during the treatment and after the treatment.