Determination of the avidity of IgG class antibodies is necessary to obtain data on the duration of infection, possible determination of the duration of CMVI and the duration of primary infection. This is due to the fact that in the first three to four months after infection, antibodies with low avidity are synthesized, that is, having weak antigen binding strength. Then begins the production of antibodies with borderline (medium) avidity and high-avidity antibodies. Low-level antibodies indicate primary infection and infection within the last three to four months. The detection of antibodies with medium avidity indicates the presence of antibodies with both low and high avidity. The determination of antibodies with high avidity indicates that the infection was transmitted at least three to four months ago before the time of the study. Antibodies with high avidity are also detected in the case of the active form of CMVI during the period of reactivation (exacerbation) of persistent infection.

It is important that maternal IgG antibodies can be detected in the blood of newborns in the first six months of life, which makes it difficult and in some cases impractical to conduct this avidity test. In people with pathology of the immune system, immunodeficiency disorders, and HIV infection, the result of the study may be unreliable due to the low level of IgG class antibodies. In this case, it is recommended to conduct additional tests to detect CMVI.