<prompt> In a neonate with classic symptoms of congenital cytomegalovirus CMV infection, which one of the following tests would be most useful in establishing a diagnosis?CMV IgG titre on neonates serum at bihCMV IgG titre on mothers serum at bih of infantCMV IgM titre on neonates serum at bih and at 1 month of ageTotal IgM on neonates serum at bih  <response>: CMV IgM titre on neonates serum at bih and at 1 month of age is useful in establishing a diagnosis in a neonate. The results should indicate a rise in IgM titre. Cytomegalovirus CMV is the most common cause of congenital and perinatal viral infections. Measurement of total IgM in the infants sera at bih is nonspecific and may show false-negative and false-positive reactions. 