Avidity of IgG antibodies distinguishes primary from non-primary cytomegalovirus infection in pregnant women

Clin Diagn Virol. 1998 Jan;9(1):9-16. doi: 10.1016/s0928-0197(97)10016-2.


Background: Human cytomegalovirus (HCMV) is the most common cause of viral intrauterine infection. Fetal damage is mostly linked to maternal primary infection. It is therefore important to differentiate primary from non-primary infection in pregnant females. IgM tests often used for this purpose are not reliable enough.

Objective: To evaluate an HCMV-IgG urea-elution assay for its ability to distinguish primary from non-primary infection. In this assay, soaking the antigen-antibody complex with an urea containing solution frees antibodies with low avidity but has no influence on those with high avidity. An avidity index (AI) was calculated: AI = (OD with urea/OD without urea) x 100.

Study design: HCMV-IgG avidity was measured on a single serum of 79 patients with past infection (pregnant women, graft recipients and blood donors) and of 63 patients (78 sera) with documented seroconversion (pregnant women and graft recipients). Sixty-one pregnant women positive or equivocal for HCMV-IgM but without a documented seroconversion were included in this study.

Results: Most (72/79) of the patients with past infection had an AI > 65% and all but one had an AI > 50%. In pregnant women, in the case of a primary infection within the past 3 months, AI are usually (51/53) < 50% and never > 65%. Among the IgM positive pregnant women who lack a seroconversion history, 38 had AI > 65% suggestive of an infection that had occurred at least 3 months earlier, 11 had an AI in a grey area between 50 and 65% and 12 had an AI < 50%, suggestive of a recent primary infection.

Conclusions: In pregnant women, measurement of the IgG avidity may help to date a HCMV infection, an AI > 65% highly suggests a past infection while an AI < 50% corresponds to a recent primary infection.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Antibody Affinity / immunology
  • Cytomegalovirus Infections / immunology*
  • Cytomegalovirus Infections / virology
  • Female
  • Humans
  • Immunoenzyme Techniques
  • Immunoglobulin G / analysis*
  • Immunoglobulin G / immunology
  • Pregnancy
  • Pregnancy Complications, Infectious / immunology*
  • Pregnancy Complications, Infectious / virology


  • Immunoglobulin G