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Improvement of cytomegalovirus avidity testing by adjusting the concentration of CMV-specific IgG in test samples
Volker Dangel1, Ursula Bäder, Gisela Enders
1Institute for Virology, Infectious Diseases and Epidemology e.V. Labor Prof. Enders and Partners, Rosenbergstrasse 85, 70193 Stuttgart, Germany. dangel@labor-enders.de
Background:
Human cytomegalovirus (CMV) is the most common cause of viral intrauterine infection. Primary CMV infection in early pregnancy bears a high risk of fetal damage. Accurate measurement of CMV-specific IgG avidity may help to improve the serodiagnosis of CMV-infected women by determining the time of infection and fetal outcome.
Objectives:
To study the performance of the CMV avidity assay with the fully automated Vidas analyzer (bioMérieux) as a function of the concentration of CMV-specific IgG present in the serum sample.
Study Design:
Eighty-two serum samples were investigated from 3 clinical scenarios: 18 individuals with sera negative for CMV-specific IgG and IgM (control group), 20 pregnant women (44 samples) containing CMV-specific IgG- and IgM-antibodies suggesting acute or recent primary infection and 20 patients with evidence of past infection (CMV-IgG positive and CMV-IgM negative).
Results:
In the group with presumed acute or recent primary infection 12 of 44 sera had CMV-specific IgG values above 100 arbitrary units (AU, bioMérieux)/ml and in these cases an increase in AI was measurable upon dilution of the serum sample. In two cases, AI's were shifted towards or above the cut-off value of AI>or=0.8, indicative of past infection. Dilution of sera which were CMV-specific IgM positive and had specific IgG concentrations of
Conclusions:
The results obtained from undiluted patients' sera with high CMV-IgG concentrations indicate that falsely low avidity indices are obtained if these sera are not diluted to below an empirically determined CMV-specific IgG concentration. In addition, the cut-off value for this commercial CMV-IgG avidity assay should be revised.
