Blood test. Cytomegalovirus infection is diagnosed by a variety of blood tests. It is part of the standard battery of tests given to pregnant moms. Once you have been infected, you are immune for life. As a result, if a pregnant mom has never been infected, she needs to be very careful to stay away from sick people, many of whom might have cmv.
Blood, biopsy. Blood tests can either directly test how much of the viral dna is present in the blood, or antibody levels in the blood can indirectly show bow much virus is in the body. The other method to detect CMV is taking biopsies from the site of suspected infection and looking under the microscope.