IM screening

The IM screening test is used to determine whether you have infectious mononucleosis. This test is rapid and easy to perform, but it is not 100% accurate. More testing may be needed to confirm that the disease is mononucleosis and not another illness.

The IM screening test is requested if your doctor suspects that you have infectious mononucleosis, which causes fever, headache, swollen glands, tiredness, and malaise. Your physician 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 heterophil antibodies are negative, 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 early, but the IgG antibodies can also be found later, during the patient's recovery.

A positive result in the IM screening test, together with symptoms of mononucleosis, are the basis for a diagnosis of infectious mononucleosis. In addition to a positive reaction on the IM screening test, an infected person has a higher white blood cell count, with a higher than usual number of atypical lymphocytes. Heterophil antibodies decline after the fourth week of illness, and the 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 do not make heterophil antibodies when infected with EBV, so more specific viral tests must be used to make the diagnosis.

In young adults, an effective laboratory diagnosis can be made on a single blood sample during the acute phase of the disease with a IM test. By requesting the more extensive battery of EBV blood tests, the physician will 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 IM screening 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.