How is it used?
The IM screening test is used to determine whether you have infectious mononucleosis. This test is rapid and easy to perform (results should be available after 1 day). The results will be either positive or negative for heterophile antibodies, however, it is not 100% specific for infectious mononucleosis. More testing may be needed to confirm infectious mononucleosis and ensure symptoms are not caused by another illness.
When is it requested?
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 doctor may also detect that you have an enlarged spleen or liver.
The test will not be positive until you have been infected for approximately two weeks or longer. Other tests may need to be requested if the heterophile antibodies are negative but your doctor still suspects mononucleosis as the cause of your symptoms.
Blood tests specific for EBV infection can be used to find early infection or to confirm mononucleosis. These tests include the and antibodies to the EBV viral capsid (VCA), which can be found early in the disease. VCA IgM is only present early, but IgG antibodies can also be found later, during the patient's recovery.
What does the test result mean?
A positive result in the IM screening test, together with symptoms of mononucleosis, is the basis for a diagnosis of infectious mononucleosis. In addition to a positive reaction on the IM screening test, an infected person generally has an increased white blood cell count, with a higher than usual number of lymphocytes which may appear reactive. Heterophile 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 often do not make heterophile antibodies when infected with EBV, so more specific viral tests must be used to make the diagnosis.
Is there anything else I should know?
In young adults, an effective laboratory diagnosis can be made on a single blood sample during the acute (initial) phase of the disease with an IM screening test for heterophile antibodies. By requesting the more extensive battery of EBV blood tests, the doctor will be able to learn whether a person is susceptible to EBV, has had a recent infection, has had an EBV infection in the past, or has a reactivated EBV infection.
When the IM screening test is negative, a combination of EBV tests for and to the viral capsid antigen, IgM to the early antigen, and IgG antibody to the nuclear antigen may be requested.