Monospot Test

The Monospot test is used to determine whether you have infectious mononucleosis. This test is rapid and easy to perform, but it is not 100% specific. More testing may be needed to confirm that the disease is mononucleosis and not another illness. However, due its practicalities, the heterophile test remains the diagnostic point-of-care test of choice in many clinical settings.

The Monospot test is requested if your doctor suspects that you have infectious mononucleosis, which causes fever, headache, swollen glands, tiredness, and malaise. Your healthcare professional may detect that you have an enlarged spleen or liver.

The test will not be positive until you have been infected for about two weeks. Other tests may need to be requested if the heterophile antibodies are negative (in particular if you are still within the first week of the disease), but your doctor still suspects mononucleosis as the cause of your symptoms.

Other blood tests that are more specific to the EBV can be used to find early infection or to confirm mononucleosis. These tests include the IgM and IgG antibodies to the viral capsid antigen (VCA), which can be found early in the disease. VCA IgM is only present in the few weeks after infection, but the IgG antibodies can also be found later, during recovery. Antibodies to Epstein-Barr virus Nuclear Antigen (EBNA) may also be tested for to gain a more accurate indication of recent or previous EBV infection.

A positive result in the Monospot test, together with symptoms of mononucleosis, is the basis for a diagnosis of infectious mononucleosis. In addition to a positive reaction on the Monospot test, an infected person has a higher white blood cell count, with a higher than usual number of atypical lymphocytes. Heterophile antibodies decline after the fourth week of illness, and the Monospot test will become negative as the infection resolves.

A negative test result means that a person may not have mononucleosis or that it is too early in the illness to detect the antibodies. The test may need to be repeated if symptoms remain. Infants and young children (in particular less than four years old of age) do not make heterophile antibodies when infected with EBV, so more specific viral tests must be used to make the diagnosis.

Interpretation of Specific EBV Test results

In young adults, an effective laboratory diagnosis can be made on a single blood sample during the acute phase of the disease with a Monospot test. By requesting the more extensive battery of EBV blood tests, the healthcare professional will also be able to learn whether a person is susceptible to EBV, has had a recent infection, has had EBV infection in the past, or has a reactivated EBV infection.

When the Monospot test is negative, a combination of EBV antibody tests for IgM and IgG to the viral capsid antigen, IgM to the early antigen, and IgG antibody to the nuclear antigen may be requested, as well as antibody tests for cytomegalovirus (CMV) or Toxoplasma gondii.

The symptoms of the disease usually resolve without treatment in one to four months. Sometimes, your spleen or liver may enlarge, and you may have to limit your physical and sport activities until these organs return to normal size. Heart problems or involvement of the central nervous system are very rare. Infectious mononucleosis may cause severe liver failure in males with a very rare and inherited X-linked lymphoproliferative (XLP) syndrome immunodeficiency disorder characterized by a defective immune system.