On the other hand, the absence of swollen cervical lymph nodes and fatigue are the most useful to dismiss the idea of infectious mononucleosis as the correct diagnosis. The insensitivity of the physical examination in detecting an enlarged spleen means it should not be used as evidence against infectious mononucleosis. A physical examination may also show petechiae in the palate. Heterophile antibody test
The heterophile antibody test, or monospot test, works by agglutination of red blood cells from guinea pigs, sheep and horses. This test is specific but not particularly sensitive (with a false-negative rate of as high as 25% in the first week, 5–10% in the second, and 5% in the third). About 90% of diagnosed people have heterophile antibodies by week 3, disappearing in under a year. The antibodies involved in the test do not interact with the Epstein–Barr virus or any of its antigens.The monospot test is not recommended for general use by the CDC due to its poor accuracy. Serology
Serologic tests detect antibodies directed against the Epstein–Barr virus. Immunoglobulin G (IgG), when positive, mainly reflects a past infection, whereas immunoglobulin M (IgM) mainly reflects a current infection. EBV-targeting antibodies can also be classified according to which part of the virus they bind to:

Viral capsid antigen (VCA):Anti-VCA IgM appear early after infection, and usually, disappear within 4 to 6 weeks.
Anti-VCA IgG appears in the acute phase of EBV infection, reaches a maximum at 2 to 4 weeks after onset of symptoms and thereafter declines slightly and persists for the rest of a person’s life.Early antigen (EA)Anti-EA IgG appears in the acute phase of illness and disappears after 3 to 6 months. It is associated with having an active infection. Yet, 20% of people may have antibodies against EA for years despite having no other sign of infection.EBV nuclear antigen (EBNA)Antibody to EBNA slowly appears 2 to 4 months after the onset of symptoms and persists for the rest of a person’s life.When negative, these tests are more accurate than the heterophile antibody test in ruling out infectious mononucleosis. When positive, they feature similar specificity to the heterophile antibody test. Therefore, these tests are useful for diagnosing infectious mononucleosis in people with highly suggestive symptoms and a negative heterophile antibody test. Other tests
Epstein–Barr nuclear antigen detection. While it is not normally recognizable until several weeks into the disease and is useful for distinguishing between a recent-onset of infectious mononucleosis and symptoms caused by a previous infection. Elevated hepatic transaminase levels are highly suggestive of infectious mononucleosis, occurring in up to 50% of people. By blood film, one diagnostic criterion for infectious mononucleosis is the presence of 50% lymphocytes with at least 10% atypical lymphocytes (large, irregular nuclei), while the person also has fever, pharyngitis, and swollen lymph nodes. The atypical lymphocytes resembled monocytes when they were first discovered, thus the term "mononucleosis" was coined.