Synonyms: EBV VCA Ab VCA, IgM; EBV-VCA IgM Antibodies Present infection Why It Is Done The Epstein-Barr virus test is a blood test, or group of tests, to determine the presence or absence of antibodies in the blood stream directed against proteins of the Epstein-Barr virus, the cause of infectious mononucleosis Test Overview: The test is primarily used to detect whether first time infection (called primary infection) with the Epstein-Barr virus is currently occurring, or has occurred within a short period of time. These tests are mostly utilized in the diagnosis of Epstein-Barr virus-associated infectious mononucleosis when the more common diagnostic test, the heterophile antibody, is negative, or in situations where the infection is manifesting unusual symptoms. • IgG. IgG antibodies are found in all body fluids. They are the smallest but most abundant of the antibodies, normally comprising about 75% to 80% of all the antibodies in the body. IgG antibodies are considered the most important antibodies for fighting bacterial and viral infections. IgG antibodies are the only type of antibody that can cross the placenta. Therefore, the IgG antibodies of a pregnant woman can also help protect her baby (fetus). • IgM. IgM antibodies are the largest type of antibody. They are found in blood and lymph fluid and are the first type of antibody produced in response to an infection. They also cause other immune system cells to produce compounds that can destroy invading cells. IgM antibodies normally comprise about 5% to 10% of all the antibodies in the body. How to prepare for the test    There is no special preparation for the test.