Interpretation
Diagnosis of primary CMV is based upon the new appearance of CMV-specific IgG in an individual who was previously seronegative or the detection of CMV IgM antibody with low IgG avidity.
Women with suspected CMV infection in pregnancy should have CMV serology testing for IgG and IgM, and IgG avidity if CMV IgG and IgM are positive.
CMV IgG avidity is more useful for timing maternal infection if primary infection during pregnancy is suspected. A low CMV IgG avidity is suggestive of recent infection (<3 months); high avidity suggests infection >3 months ago; Intermediate avidity – is not informative for assessing timing of infection. The IgG avidity testing is now standard and comparable within a laboratory, although differences in the avidity index depend on the kit/ technique the laboratory used and serial results from different laboratories should be compared with caution.
Reference Intervals
Reported as High Avidity or Intermediate Avidity or Low Avidity
